apple supply demand planner case study

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Supply Demand Product Planner Apple Interview

Hello Blinders, I have upcoming interviews with the apple supply demand planner team and was wondering if I could hear people’s perspective on the process, culture and trajectory in this team. Also, they mentioned a case study as part of the process? Any insight on this would be greatly appreciated. Thanks for the help! TC:110k YOE: 3yrs

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How are you getting an SDM call at a FAANG with 3 YoE?

Or does SDM not mean Software Development Manager in this context.

Recruiter mentioned SDM as acronym. This is for Apple operations/ Supply chain rather than software development.

Supply Demand Management

This is probably the least sexy/one of the more boring roles within Apple’s operations division. Unlike Global Supply Managers you aren’t involved in contract negotiations with suppliers, aren’t traveling to supplier sites etc. You will instead primarily build long Term Mass Production Schedule forecasts which are only used as a reference point on what to track against. What role are you in at GS? I’d say it’s akin to a back office role at GS

Im in IB, but want a better WLB. Recruiter mentioned a 170k TC which is on par with analyst year 2/3 pay.

Do you know what the hours look like?

I have worked in the Supply Demand Team. I would say work is good, lot of Analytics. I would not call it boring/back office. SDM actually provides the Forecast for GSM/Ops to execute. Management/Team is good, good culture and WLB compared to a lot of other Operations Teams at Apple.

Hi, can you share your experience? A recruiter reached to me and asked to apply.

At what stage are you?

Scheduled phone call with the recruiter. Background info on me- I’m in DC, do FP&A for a GSE. Left MS last year. 3 YOE. TC: ~140 Looking for info on comp, type of work, exit ops etc.

Hi! Can you share your experience with the case study?

Do you work at Apple?

Hi! I’m currently interviewing for this role and have the THA scheduled this weekend and an interview next Monday - can anyone please share how your experience was, what to expect and any tips/tricks? TIA!

hi, what about your interview, can you share some tips and the presentation case study

This is a really crappy team- low pay, very manual redundant ops work, toxic people. Run away!! Hope you are not in already.

Currently in the second round of interviews with the case. Any tips on preparation or insight you can provide?

Hi, can you share about the case study, what should I prepare. Thanks

Does anyone know what to expect for an Apple "WorldWide Supply Demand Planner" technical interview?

I have an upcoming interview for a WorldWide Supply Demand Chain Planner position  at Apple that requires a technical portion of the interview, as well as a full case study later on.

Can someone familiar with the role describe the day to day and what to expect in terms of technical parts of the supply demand interview?

Feel free to contact me, then we can have a call on this topic :)

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Apple’s supply chain transformation

In 2022, Apple lost US$1.5 billion in Black Friday sales due to iPhone supply constraints. One in three retail stores across the US and Europe experienced stockouts of the new iPhone 14 Pro. China sales were down more than 30% year on year. Apple’s stock had dropped 29% in 2022. China’s zero-Covid policy resulted in massive lockdowns that made factory working conditions unbearable. In the second half of 2022, many Chinese workers quit their jobs at Apple’s Foxconn facilities. The Russia-Ukraine war that started in February 2022 and the ensuing Western sanctions spurred an unprecedented global energy crisis and double-digit inflation. Now that supply chain disruptions, component shortages and rising geopolitical tensions had become a reality, Apple had to decide on a transformation, knowing that the transition presented difficult trade-offs and would take years to complete: (1) Which elements to change in the company’s global value chain? How to approach change without hurting manufacturing continuity, product quality, revenue and profitability? (2) Should Apple further drive its vertical integration in the design of chips, semiconductors, screens and assembly? Or should it adopt the Android phone manufacturers’ model and develop a broader base of suppliers?

• Define Apple’s supply chain competitive advantages and dependencies
• Analyze the factors driving the need for transformation and their impact
• Assess the options available in Apple’s global value chain adaptation to a deglobalizing world
• Evaluate the strategy and tactics for Apple’s supply chain transformation

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Apple Inc.: Global Supply Chain Management

Nov 12, 2020

• Apple Podcasts

Fraser Johnson , professor of operations management at the Ivey Business School, joins host Matt Quin to take another look at his  award-winning  case,  Apple Inc.: Managing a Global Supply Chain  (2014), as well as the recently published update,  Apple Inc.: Global Supply Chain Management  (2020).  In this episode, Johnson and Quin discuss Apple's business model, how he has brought the company into the classroom over the years, and why junior faculty ought to consider writing cases. Professor Johnson is the Leenders Supply Chain Management Association Chair at the Ivey Business School, Western University, where he teaches courses in supply chain management and operations. Johnson is also the Director of the  Ivey Purchasing Managers Index , one of the most widely watched and utilized indicators of future economic activity in Canada.

Hi, I'm at Quinn. Thanks for joining us for decision point from Ivy Publishing at the Ivy Business School. Today we returned to another award winning and best selling case. Apple INC managing a global supply chain, originally published in two thousand and fourteen. Authoring Professor Frasier Johnson from the Ivy Business School, presents a snapshot of Apple up against competitors such as blackberry and Samsu. Unlike other companies with leading supply chains, such as Walmart, apple's approach to supply chain strategy and supplier management padded, investing far less in assets to support distribution. Instead, the company is now famous for its focus on innovation, new product development and brand management. In this episode we ask Professor Johnson about how apple was able to use its business model and supply chain strategy to help it continue capturing significant value from hardware sales. We also take a look at the updated two thousand and twenty case in the increased complexity for apple as it continues to add services in products to compete in the mature smartphone market. I hope you enjoyed today's episode. So, Frasier, thanks very much for joining us today. Apple was a really different company in two thousand and fourteen. What prompted you to write the case then, and how have you audit what's changed as you've taught it throughout the years? Well, apples a fascinating company. A lot of the cases that are done in the supply chain area tend to be with traditional manufacturing companies like Toyota or large retailers like Walmart, and one of the things that really interested me about apple was or business model with the IPHONE, with these annual product introductions, with big spikes in demand, and exactly how were they able to get their supply chain organized to be able to meet these big peaks in demand that they were facing. So the great thing about cases is it puts the student in the seat of a protagonist. This particular case Examines Apple from the perspective of Jessica Grant. She's an analyst with a Toronto based Money Management Firm. You, as an author, did a great job of giving students a primer of how apple was able to reach the margins with the iphones through supplier relationships and really tight coordination of the supply chain. Can you remind listeners what's at stake in the case for apple when it was set in two thousand and fourteen. Well, apple was one of the early innovators in the smartphone business and if you take a look at what's happened to the company over the last decade or so, the iphone is a way that apple connects with their consumers. Those they do things like sell services to individuals. Really, you know, the analogy that I use in the teaching note is that the iphone represents the the the razor that they used to be able to sell the blades to the consumers. So as apple looks to expand as market in the smartphone business, really what it does is give them a platform to be able to connect with their consumers. And from the students perspective, you're putting them in the role of the analyst in the case allows them to take a look at the entire business operation as opposed to taking the role of a functional executive with a specific functional related problem. So let's talk teaching notes for a second, because you've written a lot of case as many of them are best sellers. Let's dive into the teaching note part of this. In the teaching note you mentioned flexibility as a key part of the apple supplier management strategy. With recently apple moving away from mentell process. There's in away from Samsung as a screen supplier. It seems that the company is really continuing to embrace this approach of flexibility. What do you see in the company? Back in two thousand and seven when apple launched the iphone, they basically outsourced everything. HMM. So to bring a iphone to market they had to work closely with their suppliers. And the other interesting part of this is a short product life cycle of the IPHONE. They bring a new product ote every year and that was one of the it's one of the other important parts of the case. How do you work with suppliers where you're constantly launching and relaunching a new product every year, in selling product in the in the millions? So if you take a look at a company like Walmart, for example, they practice every day low pricing, so they try to minimize the bull whip effect and provide stable demand so they can work with their suppliers to reduce their total costs. Apples a complete opposite. They embrace variability. They have, as I said earlier, these annual releases with huge product introductions, with high volumes and then volumes taper off slowly until they bring out a new product and repeat the process all over again. And so you've built this in these comparators, in in the narratives. So one of the things that we know is important about the uptake of a case, in the sales of a case, is also the teaching note, and you write great teaching notes. You've mentioned apple versus Walmart. What are some other things that you try to include in a teaching note to help a faculty member use it in the classroom? What are your keys to success? Well, you know, what you want is, as somebody writing a case, to have a teaching note that resonates with other instructors. So when I say resonates, it's got to be something that they can relate to. It doesn't want to be so complicated that when they read the case and then take a look at the teaching note, become intimidated with the material that they see. They have to be able to understand it. They'd be had to be able to translate the material that you provided the teaching note into a classroom setting, so being able to talk about the issues at instructors face, including a teaching strategy appropriate questions to ask as part of delivery of the material are all very important. The other thing that I think is important to recognize is it before the case is completed, you've also got to write the teaching note. So don't publish the case and then come back to the teaching note a month later or two months later. Rate both documents simultaneously, because you have to use your teaching note as a quality control check to make sure that there's enough information in the case for the students and the instructors to be able to complete the analysis properly. And I know something you've done and our other colleagues have done is way to finalize that teaching note, if you will, until you've taught it a couple times and see how certain questions go or there might be some new information that comes out that you can include. So I know you've done that a few times as well. Right. Yeah, for many of the cases that I've written I will go back to the great staff at I've publishing and make revisions to the teaching note and perhaps to the case I'm talking about, minor at it to make in case issues have come up in the class discussion and I can help clarify the case by making qualifying statements. Sometimes when you're right a case, even with the editing process that you go through, sometimes students don't always interpret the information properly. So gives me a chance to be able to go back in and, you know, just a couple of sentences put not tend to clarify what certain peoples of data mean. For example, one of the tips that you gave is to try to not make things overly complicated. At the time of the case there's a lot happening at at apple with the five c being released. Profit margins were down slightly from, you know, two thousand and nine to two thousand and eleven. What do you think of and consider as you're writing a case to maintain that focus without, you know, there's a lot that you can put in a case. How do you remain so focused as an author? Well, I think that you're right a case in a particular point of time and as you as you say, you know, a lot has happened at apple in the last decade, or I guess thirteen years, since they brought out the first iphone, and you know the way that I view a lot of cases. You like my one an apple my other cases on Walmart and Amazon, is that they're almost live cases in the sense that, you know, I keep crack of what's going on in these organizations throughout the year before I teach the case so that we can use the information in the case is kind of a launching board, but we can also I can also incorporate through the introduction of power point slides, for example, and other information in terms of more recent developments. In the case of Apple, you see them, for example, insourcing more product buying the chip division from Intel and moving more to insourcing mode as opposed to an outsourcing mode, and that's the kind of stuff that you can incorporate into the class discussion. You've mentioned that you've released an updated case, which is great. We encourage faculty to do that and authors to do that. We welcome that and it's a smart thing to do because the cases evolve, the companies evolved in the situations, in the environment that the business is working evolved as well. Could you talk a little bit about the new case and the new complexities for Apple? Is As we sit here, in two thousand and twenty I wrote the first apple case, as you stated earlier, in two thousand and fourteen and if you take a look at what was happening to apple at that point, the sales for iphones were on the upsway and you know, if apple had a problem at that point, it was simply keeping up with demand. Now, if you take a look at what's happening in two thousand and twenty, the situation that the company faces and the challenges for its supply chain or are a lot different. As we talked about earlier, it's more moved to more of an insourcing model. On the other side of it, sales of the IPHONE are now starting to flatten out and the smartphone market is starting to mature. So we've see in back in two thousand and fourteen, apple competing in an environment where the markets growing margins are pretty healthy and it's having trouble keeping up with the man to in two thousand and twenty, where you're facing consecutive years of sales declines of the IPHONE and a maturing market with a lot of price pressure on margins. The other thing that you see with apple in two thousand and twenty compared to two thousand and fourteen is an increased emphasis on services. So one of the things that we can talk about in the new case is how does apple manage its services supply chain? So it really gives you a double edge. On one side we can talk about changes to the iphone and what apple does to manage its iphone successfully, but also how do they use the iphone in terms of its relationships and connectivity with its customers as part of its services supply chain? I've mentioned before how popular this case is. It's been climbing up the best seller list for years. Why do you think that is it? Is it the brand? Is it because the student can hold this thing in their hands and have a relation with with the company? What do you think is made us so popular? You know, I like to say cases like this teach themselves, and you know it's an overused line maybe in some areas, but students are familiar with the company, instructors are familiar with the company. The brand is strong. Even students that don't necessarily get excited about coming to class and talking in a case discussion do like the technology companies and I think there's something in the case for people that most people, particularly students, can relate to in terms of the technology and how they use their iphones and even the debate among the students in the class, among the iphone users versus the non iphone users. So every time I teach the case I ask you know, who's using apple products, and iphones included, and who's not using them, and why is that? You know, why do you like apple? Why do you use your products? On the other end of the spectrum, who are the Anti Apple people and why have they made a conscious decision not to participate in what I call in my new case apple ecosystem? And that kind of allows us to talk about the company strategy, which then evolves into a further more detailed discussion about how they're able to support Tho strategy with their supply chain capabilities. Yeah, it's a very accessible for for students of many Undergrad students, Grad students, high school students, can they can all take a different approach with it, but apple is a company is pretty accessible. Have there been any challenges or surprises when you've taught this where you go, oh, that's a different perspective or I have to remember to the include that in my next version of the case. Anything that comes to mind. The major event for me was in two thousand and nineteen as I was teaching the case and my supply chain management elective. And you know, as I'm standing up in front of the class talking about what's happening with a company in two thousand and nineteen, about exactly how much it changed at at Apple, and you know that point. You know after I, as I do after every class, I make notes to myself in terms of things that I want to remember for the following year, I made the decision that I commit the time to updating the case and writing and ended up doing that writing the case this year. So to me, you know, when you deal with cases like apple, you know a lot of the changes and things that happen, both in the classroom as a result of what happens at the company and as part of your preparation in terms of teaching the case. Is kind of evolutionary. Is of most revolutionary. Yeah, but eventually, you know, with companies like this, you do reach a point where you've got to think about revising the product, and that's one thing I want to give as a really good tip, and I don't want to overlook this, I'm just looking at some notes I've got here, is that the importance of immediately after the class, taking down notes as an instructor H who's either taught this case a number of times or just new to it. All the great case teachers that I've seen makeup point immediately, even at the breaks, of writing down some notes about ways it could be done differently or different things to approach or something that didn't go so well. So I want to make sure that if we hit that point for those that are listening, because that's such a great tip that I don't want to overlook. So anything else that you make a point of doing right before class or during a break or right after the class as a process for case teaching? Yeah, yeah, I think that this is maybe a minor point, but I think a relevant one. I think regardless of how many times you've taught a case and regardless of whether or not you're the one that wrote the case, and sometimes I think people that write cases can be too overconfident in terms of their level of understanding with the material to invest the time before class to get ready, regret, regardless of how many times you've taught the case. So don't just pick the file up and walk into class. US remind yourself about the essential details of the case and the case facts and think about how you're going to manage the conversation with the student. And, as I said earlier the debrief after class, every time I teach a case, I sit in my office after class and make note to my teach on the front of my teaching plan in terms of things that I would adjuster do differently or things that I want to remind myself worked well and to do. And that regular pays off, because I've seen you teach. You've welcome to a lot of our team members from I be publishing to watch a teach. So I've seen it at work. As we wrap up today on the discussion, I want to come back to the writing of cases. Do you have anything that stands out to you that you wish somebody had told you when you were just starting to write cases? Any any tips for new case writers as they ventured down this road? I think that you, as a new faculty member, writing cases is a is a great way to first of all learn about management practice and if you're writing feel cases working with companies in terms of material or case development, it gives you a chance to be able to talk to managers about some of the issues that they're facing and it keeps you current and, you know, being able to and you can do that through your research, certainly, but writing cases is another way to be able to stay in touch with what's going on in terms of management practice. The second point is a writing cases helps you establish credibility with your students. Students pay attention to the material that's being used in terms of the case studies, and if your name's on the author list of the case study that they're using, it tells the students that you know you're doing work in this area. These chances are they're probably not reading your research and helps establish some credibility in terms of your familiarity with the subject matter and the material that you're using in class. Well, that's fantastic. Thank you so much, Frasier, for taking the time to speak with us and, moreover, working with our team on publishing cases and bringing cases to the class. I know when we get a submission from you, our team always enjoys the process, so thank you for that as well. It's my pleasure. Thanks for the great job that everybody to I be publishing, does and supporting the word that the faculty does in terms of writing and publishing cases. If you enjoyed today's episode, subscribe to Decision Point on spotify or wherever you listen. Be sure to check out the show notes for links to cases, resources and more. have any feedback, send us an email at cases at IV DOC A.

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How Apple Is Organized for Innovation

• Joel M. Podolny
• Morten T. Hansen

When Steve Jobs returned to Apple, in 1997, it had a conventional structure for a company of its size and scope. It was divided into business units, each with its own P&L responsibilities. Believing that conventional management had stifled innovation, Jobs laid off the general managers of all the business units (in a single day), put the entire company under one P&L, and combined the disparate functional departments of the business units into one functional organization. Although such a structure is common for small entrepreneurial firms, Apple—remarkably—retains it today, even though the company is nearly 40 times as large in terms of revenue and far more complex than it was in 1997. In this article the authors discuss the innovation benefits and leadership challenges of Apple’s distinctive and ever-evolving organizational model in the belief that it may be useful for other companies competing in rapidly changing environments.

It’s about experts leading experts.

Idea in Brief

The challenge.

Major companies competing in many industries struggle to stay abreast of rapidly changing technologies.

One Major Cause

They are typically organized into business units, each with its own set of functions. Thus the key decision makers—the unit leaders—lack a deep understanding of all the domains that answer to them.

The Apple Model

The company is organized around functions, and expertise aligns with decision rights. Leaders are cross-functionally collaborative and deeply knowledgeable about details.

Apple is well-known for its innovations in hardware, software, and services. Thanks to them, it grew from some 8,000 employees and $7 billion in revenue in 1997, the year Steve Jobs returned, to 137,000 employees and $260 billion in revenue in 2019. Much less well-known are the organizational design and the associated leadership model that have played a crucial role in the company’s innovation success.

• Joel M. Podolny is the dean and vice president of Apple University in Cupertino, California. The former dean of the Yale School of Management, Podolny was a professor at Harvard Business School and the Stanford Graduate School of Business.
• MH Morten T. Hansen is a professor at the University of California, Berkeley, and a faculty member at Apple University, Apple. He is the author of Great at Work and Collaboration and coauthor of Great by Choice . He was named one of the top management thinkers in the world by the Thinkers50 in 2019. MortentHansen

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Supply Chain Innovation

Designed by apple in california. made by people everywhere..

Business can and should be a force for good. We uphold our values everywhere we operate, supporting the people and communities across our supply chain, and working to protect the planet we all share.

A global supply chain.

Studio Display assembly, China mainland

Apple products are made all over the world.

Thousands of businesses and millions of people in more than 50 countries and regions are part of our supply chain, contributing their skills, talents, and efforts to help build, deliver, repair, and recycle our products.

Our suppliers are required to meet the strict standards of the Apple Supplier Code of Conduct , no matter where they operate or what type of goods, services, or labor they provide to Apple.

Counterclockwise from top: Apple Watch assembly, Vietnam; Apple Watch band manufacturing, Japan; Mac Pro assembly, United States

We listen. And act.

Component manufacturing, Switzerland

We encourage everyone across our supply chain to share feedback. And we’re focused on ways to amplify their voices. We interview and survey hundreds of thousands of supplier employees, and provide hotlines so they can anonymously raise concerns directly to Apple. We use this feedback to support our suppliers in strengthening their operations and providing the best possible experience for their employees.

We investigate reported concerns quickly, with Apple experts typically arriving onsite within 24 to 48 hours. Apple has zero tolerance for retaliation, and any supplier found to have retaliated against an employee for raising a concern faces immediate consequences, up to and including termination of their business with Apple. We require our suppliers to promptly address any issues, and we regularly check on their progress until we confirm that all necessary actions have been taken.

If suppliers are unwilling or unable to correct any issues, they risk removal from our supply chain. Since 2009, we have removed 25 manufacturing supplier facilities and 231 smelters, refiners, and manufacturers of materials from our supply chain for failing to meet our standards.

Counterclockwise from top: Logistics, United States; Apple Watch assembly, Vietnam; iPhone assembly, China mainland

supplier employees directly engaged by Apple about their workplace experience in 2023

improvements made to supplier workplaces based on employee feedback in 2023, mostly focused on services like transportation and dining

people at 35 supplier sites reached by our hotline awareness campaign, which provides knowledge on how to raise workplace concerns

supplier employees contacted following interviews to ensure that they didn’t experience retaliation as a result of their participation

Labor and human rights at the foundation.

Apple Watch assembly, Vietnam

Everyone has the right to work in a safe and healthy environment where they’re treated with respect and dignity. We uphold these rights with every decision we make, including the suppliers we choose to work with, the materials we select for our products, and the processes and equipment we use to make them. We work closely with our suppliers to uphold the highest standards of labor and human rights everywhere our business reaches.

Our standards apply globally, regardless of where people live or work or which job they do. We require our suppliers to educate their employees on their workplace rights, including how to share feedback if their rights aren’t being respected. With the help of experts, nonprofit organizations, government agencies, and workers themselves, we consistently strengthen our requirements and programs to make sure they continue to meet the needs of people across our supply chain.

From top to bottom: Component manufacturing, India; Studio Display assembly, China mainland

supplier employees trained on their workplace rights since 2008

supplier employees’ working hours reviewed weekly to verify compliance with our standards

education and training sessions delivered through the Apple Supplier Employee Development Fund (SEDF)

Dedicated to continuous improvement.

Product personalization, United States

Before a prospective supplier enters our supply chain, we assess their ability to meet our standards and identify areas for improvement. We hold suppliers accountable for our strict standards through regular, rigorous onsite assessments. Conducted by independent third-party auditors, these assessments look at every detail of a supplier’s operations through worker and management interviews, detailed site walkthroughs, and thorough reviews of documentation.

Suppliers must fix any violation of our standards under the supervision of Apple experts and take steps to prevent the issues from happening again. Any suppliers that are unable or unwilling to improve their operations to meet our requirements risk removal from our supply chain.

We also support our suppliers’ continual learning and improvement by having Apple experts share knowledge, advise on best practices, and design learning plans customized to the needs of each site.

Clockwise from top left: HomePod assembly, Vietnam; Component manufacturing, Germany; Fiber-based packaging production, Austria

assessments of supplier facilities conducted in 2023, including 203 unannounced visits

of prospective suppliers prevented from entering our supply chain since 2020 for being unable or unwilling to meet our requirements

The strongest standards in hiring.

Mac Pro assembly, United States

Apple has no tolerance for forced labor. Our policies that prevent forced labor apply globally, regardless of a person’s job, location, or how they were hired. We require that job recruitment processes be free and fair, prohibiting practices such as charging fees to secure a job — even where it’s allowed by law. We’ve partnered with the International Organization for Migration (IOM), a United Nations agency, to create easy-to-use tools that help suppliers recruit people ethically and with respect for their human rights.

Our work to prevent forced labor extends throughout the employment journey, and we verify that suppliers are meeting our standards every time we engage with them, including during assessments.

Learn more about our efforts to prevent forced labor (PDF)

instances found where people were forced to work in our supply chain in 2023

people trained on the industry-leading tools in the Apple Responsible Labor Recruitment Due Diligence Toolkit in 2023

in recruitment fees paid back by suppliers to more than 37,700 employees since 2008 due to Apple’s zero-fees policy

Skills that open doors.

Through the Apple Education Hub, people across our supply chain are able to access technical education and resources on topics such as personal development, leadership, computer science, coding, robotics, recycling, and advanced manufacturing. These programs enrich supplier employees’ workplace experiences and provide the skills needed to pursue opportunities in highly technical fields. For example, graduates of our Swift coding program have launched apps on the App Store, meeting the high bar required for publication.

We partner with leading experts such as the Council for Adult and Experiential Learning (CAEL) in the United States, Zhejiang University in China mainland, and St. John’s Medical College in India to ensure that our programs are innovative, meaningful, and connected to relevant opportunities in local job markets.

Clockwise from top: Component manufacturing, Japan; Component manufacturing, India; Mac Pro assembly, United States

technical or management positions attained by graduates of our education programs

supplier employees who have graduated from our Swift coding program since 2017

The Supplier Employee Development Fund.

Apple Education Hub, China mainland

Education is a powerful equalizing force, and we are committed to providing opportunities for the people in our supply chain to learn and grow. In 2022, we announced a $50 million Supplier Employee Development Fund (SEDF) to further invest in people in our supply chain. Through the fund’s Apple Education Hub, we’re expanding access to educational opportunities for supplier employees and their surrounding communities.

In partnership with local academic institutions and non-governmental organizations (NGOs), the Apple Education Hub helps supplier employees develop the skills necessary to pursue new opportunities in our supply chain, as well as better manage their health and well-being.

From top to bottom: Component manufacturing, United States; Retail janitorial services, United States

supplier employee participants in learning and development opportunities through the Apple Education Hub in 2023

supplier employee participants in our education programs since 2008

Health starts with knowledge.

Education programs, India

Education programs, India

We’re committed to cultivating a supply chain where people can thrive — inside and outside work. This means providing the people in our supply chain with the tools needed to focus on their physical and mental health. Since 2017, millions of supplier employees have benefited from training on essential topics such as nutrition, reproductive health, early disease detection, and mental health. These programs are tailored to meet the needs of local supplier employee populations, equipping them with important knowledge and skills to take control of their own health, which they can then share with their communities to multiply the impact.

Counterclockwise from top: Health and wellness education, Vietnam; Health and wellness education, India; iPhone assembly, China mainland

people reached by our health and wellness programs since 2017

participants in our mental well-being programs in 2023

Advanced. Manufacturing.

Component manufacturing, United States

As we continue to drive innovation in our products, the machines used to build them must also advance. That’s why we’re always reviewing and strengthening our machine safety programs to help keep the people who operate manufacturing equipment safe on the job. We require suppliers to design safer equipment from the start and to conduct regular trainings on topics such as the use of safety devices, inspection basics, automation safety, and hazards associated with moving parts. We also require suppliers to regularly inspect equipment and safety procedures to confirm that machines remain in safe working condition and that the rules put in place to keep people safe are being enforced and followed. If we do find issues, we work with suppliers to correct them and prevent them from happening again.

Counterclockwise from top: Component manufacturing, Japan; Component manufacturing, China mainland; Component manufacturing, Germany

supplier sites enrolled in our new enhanced machine safety training in 2023

machines inspected for safety risks at 112 key supplier sites around the world in 2023

A culture of safety.

iMac assembly, Ireland

iMac assembly, Ireland

Everyone has the right to be safe at work, and we work hard to verify that the materials, machines, and processes used to make our products safeguard the health and safety of the people in our supply chain. We consistently update our industry-leading health and safety standards and confirm that our suppliers meet those standards through regular inspections. We also partner with our suppliers to build a workplace culture that puts health and safety at the forefront every day, including by offering training materials and providing ways for employees to speak up if they identify opportunities to improve safety practices.

Counterclockwise from top: Fiber-based packaging production, Austria; Mac Pro assembly, United States; Component manufacturing, Germany

supplier sites participated in safety training in 2023

Facility Readiness Assessments conducted before manufacturing began in 2023

Leading the way on smarter chemistry.

iPad assembly, Vietnam

Keeping workers and customers safe is a top priority that guides the decisions we make about the materials we use in our products. We require our suppliers to follow our industry-leading chemical safety standards to make sure that employees, communities, and the environment are protected against chemical hazards. This includes working together to use safer materials in our products and manufacturing processes, such as in the cleaners used during product assembly. By collaborating with leading experts and nonprofit organizations, we’re accelerating the adoption of safer chemicals across the electronics industry, fostering safer working conditions for people far beyond our own supply chain.

Counterclockwise from top: MacBook Pro assembly, China mainland; iPhone assembly, China mainland; Supplier water treatment facility, United States

suppliers reported data on the chemicals used in their facilities in 2023

new safer cleaners approved for use in our supply chain in 2023, with a total of 175 approved cleaners deployed to our suppliers since 2020

A carbon neutral supply chain by 2030.

Apple’s worldwide corporate operations have been carbon neutral since 2020, and we’ve set a goal to become carbon neutral across our entire supply chain, including the lifetime use of our products, by 2030.

Reaching our Apple 2030 goal means we first need to continue reducing the carbon emissions from our manufacturing processes. To make this happen, we’re designing our products to be less carbon-intensive, increasing our use of recycled and renewable materials, and transitioning our entire supply chain to 100 percent renewable energy. We’ll then use carbon removal to address the small amount of remaining emissions, starting with high-quality nature-based solutions, like those in Apple’s Restore Fund.

We’ve also called on our suppliers to decarbonize their Apple production by 2030, and we’re helping them get there through targeted programs and training that aim to improve their energy efficiency and identify sources of high-quality renewable energy.

Learn more about Apple 2030

Counterclockwise from top: Supplier solar array installation, Switzerland; Apple Watch band manufacturing, Japan; Apple Watch assembly, Vietnam

of Apple suppliers expected to be carbon neutral for their Apple production by 2030

gigawatts of renewable energy operational in the Apple supply chain

Environmental rights are human rights.

Responsibly managed forest, Austria

The global impacts of climate change are becoming more apparent by the day. Our approach to protecting the planet considers not only the environmental implications of every decision we make, but also the impact of those decisions on people, particularly those living and working in communities disproportionately affected by climate change. That’s why we consider our supply chain in the context of the local communities where our suppliers operate.

Low-income and historically marginalized communities too often bear the brunt of the effects of climate change. As part of our Racial Equity and Justice Initiative (REJI), we created the Impact Accelerator for Black-, Latinx-, and Indigenous-owned businesses focused on environmental solutions. The Impact Accelerator is just one way we’re helping ensure that those most affected by environmental challenges are also helping design solutions that dismantle the systemic barriers to addressing them.

From top to bottom: Supplier solar array installation, Germany; Supplier water treatment facility, United States

Black-, Latinx-, and Indigenous-owned businesses participated in the Impact Accelerator since 2020

A zero waste mindset.

iPhone assembly, China mainland

We’re dedicated to minimizing our resource use and waste as we build our products. We require our suppliers to avoid sending waste to landfills by implementing recycling and reuse programs and developing innovative materials and recycling strategies. Today, all established final assembly sites for major Apple products are Zero Waste Certified.

Water is a critical resource shared by people and ecosystems around the world, and we’re working to protect it for future generations. Through our Clean Water Program, we’re helping suppliers reduce their water usage, promote water recycling, and prevent water pollution. Since the launch of this program in 2015, 20 of our suppliers’ facilities have achieved certification through the Alliance for Water Stewardship (AWS), the world’s leading water stewardship organization. Earning this certification requires suppliers to adopt industry-leading water conservation and stewardship practices while also engaging with their community to protect resources across their local water basin.

From top to bottom: Apple Watch band manufacturing, Japan; HomePod assembly, Vietnam

metric tons of waste diverted from landfills by Apple suppliers in 2023

gallons of freshwater saved through Apple’s Clean Water Program since 2013

Our journey to 100% recycled and renewable.

Materials recovered by Daisy, Apple’s iPhone disassembly robot, United States

Our goal is to one day build our products using only recycled and renewable materials and eliminate our reliance on mining. Each year, we move closer to that goal, with more components being made with 100 percent recycled or renewable materials. Effectively disassembling and recycling our products after their use is also a key part of our work to support a circular economy. These processes help recover valuable materials that can be used again, making the best use of limited resources and enabling us to design and build the next generation of devices to be even better for people and the planet. That’s why we help our suppliers efficiently and safely recycle our products, by providing Recycler Guides and conducting assessments to verify that they’re meeting our standards.

We maintain strict standards for the responsible sourcing of materials — whether primary or recycled. Since Apple doesn’t directly purchase or procure primary materials, we work closely with our suppliers to uphold these standards and work with partners to improve conditions in and around mining communities.

Clockwise from top: Daisy, Apple’s iPhone disassembly robot, United States; Supplier hydroelectric energy facility, Austria; Recycling, Singapore

responsibly sourced key materials in batteries, whether primary or recycled

recycled cobalt targeted to be used in all Apple-designed batteries by 2025 *

recycled rare earth elements targeted to be used in all magnets across Apple products by 2025

Read our 2024 reports to learn more about our dedication to people and the planet.

More from Apple on our global supply chain.

Your feedback makes a difference..

We welcome your thoughts, questions, and ideas about our global supply chain.

Our values lead the way.

Environment.

We’re committed to bringing our net emissions to zero across our entire carbon footprint by 2030.

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We’re holding ourselves accountable for creating a culture where everyone belongs.

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We’re addressing systemic racism by expanding opportunities for communities of color globally.

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Award winner: Apple Inc: Global Supply Chain Management

This case won the Production and Operations Management category at The Case Centre Awards and Competitions 2022 .  #CaseAwards2022

View the video of the award presentation on 27 May 2022 .

Author perspective

Who – the protagonist.

Tim Cook , Chief Executive Officer (CEO) and former Chief Operating Officer (COO) of technology giant Apple Inc .

As of February 2020, Apple Inc. had revenues of approximately US$265 billion making it the most valued company on the planet. Its lead product was the iPhone, with over 1.6 billion sold since it was introduced in 2007. To cope with demand, Apple had a complex supply chain of 200 suppliers located in over 800 production facilities, across 43 countries.

With the smartphone market starting to mature, challenges by new competitors and, according to critics, no game-changing new products in development, Apple needed to take steps to diversify from its dependence on the iPhone.

Apple were planning to launch a new suite of services including entertainment, news, video games and financial services, so Tim Cook needed to consider what changes should be made to Apple’s global supply chain to support its strategic objectives. What capabilities would it need as Apple’s business model continued to evolve?

This case is set in February 2020, 44 years after the company was founded.

Apple’s primary iPhone suppliers include companies in the US, China, Japan, South Korea, Switzerland and the Netherlands, but 90% of product assembly is done in China before being transported back to the US.

It would be difficult for Tim Cook and Apple to duplicate the capabilities and advantages offered by its Chinese suppliers, but their diversification from iPhones into wearables and services would provide additional challenges. New supply chains for different products and technologies were required along with content for entertainment and streaming services. As Apple’s business model evolved, Cook had to ensure the global supply chain continued to support it.

AUTHOR PERSPECTIVE 

This is the second win for P Fraser Johnson in the Production and Operations Management category for a case on Apple, following his win in 2016 . It is also the seventh award win for Ivey Business School.

Winning the award

Fraser said: “Naturally it is always terrific to be recognised in my profession by an outstanding organisation such as The Case Centre. With the many cases that are written each year in the operations management field, I was understandably surprised to hear that my Apple case was the 2022 winner of The Case Centre Award for my discipline.

“As a professor at the Ivey Business School, the ability to write cases that resonate with students and instructors is a critical aspect of my job and career. Writing cases that instructors want to adopt in their courses helps promote the use of the case method, which is incredibly important to me personally.”

Case popularity

He continued: “I think this case stands out for two reasons. First, it effectively describes the evolution of Apple as an organisation, through the good times and bad times, and how its supply chain strategy evolved and became a critical strength and capability. Everyone knows about Apple and the products that the company makes. The case makes students think about how Apple has been able to support its business and product strategies through unique supply chain capabilities.

“Second, the case is supported with a thorough teaching note. Effective teaching notes are essential in helping instructors deliver a great classroom experience with the case.”

Writing the case

Fraser explained: “First, this case is based on published sources. Gathering data from a wide range of sources is important. Accessing published articles, press releases, analyst reports and financial records are but a few avenues.

“Second, keep the case focused on a central topic and avoid extraneous information. It is easy to load the case up with interesting data, but it needs to be relevant to the issue(s) in the case.

“Lastly, have the case focused on a decision. Do not tell a story, the newspapers can handle that job. Students should use the issue(s) and decision, in the role of the protagonist, to focus their analysis. Without a decision in the case, students will not be able to properly structure their analysis and preparation.”

Case writing advice

He continued: “A case on a company with a well-known brand name helps, but there are two other important factors. First, the issue in the case needs to be interesting and relevant, which helps provide the basis for a good class discussion. Second, a strong teaching note helps provide instructors with thorough analysis and guidance on how to deliver the case in the classroom.”

Teaching the case

Fraser commented: “This case is one of the most popular in my supply chain elective. Apple is the largest company in the world (by market capitalisation) a brand that every student is familiar with – as a result students have views about the company, both positive and negative. Students can then relate their personal experience with the information in the case. It is an easy case to teach with a lot of discussion.”

The protagonist

Educators can login to view a free educator preview copy of this case and its teaching note.

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Open Access

Peer-reviewed

Research Article

Modelling the water supply-demand relationship under climate change in the Buffalo River catchment, South Africa

Roles Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Software, Validation, Visualization, Writing – original draft

* E-mail: [email protected]

Affiliations Bioresources Engineering Programme, School of Engineering, University of KwaZulu-Natal, Scottsville, Pietermaritzburg, South Africa, Centre of Transformative Agricultural and Food Systems, School of Agricultural, Earth and Environmental Sciences, University of KwaZulu-Natal, Scottsville, Pietermaritzburg, South Africa

Roles Conceptualization, Formal analysis, Methodology, Project administration, Resources, Supervision, Validation, Writing – review & editing

Affiliations Bioresources Engineering Programme, School of Engineering, University of KwaZulu-Natal, Scottsville, Pietermaritzburg, South Africa, Centre of Transformative Agricultural and Food Systems, School of Agricultural, Earth and Environmental Sciences, University of KwaZulu-Natal, Scottsville, Pietermaritzburg, South Africa, Centre for Water Resources Research, School of Engineering, University of KwaZulu-Natal, Scottsville, Pietermaritzburg, South Africa

Roles Conceptualization, Formal analysis, Funding acquisition, Methodology, Project administration, Resources, Supervision, Validation, Writing – review & editing

Affiliations Centre of Transformative Agricultural and Food Systems, School of Agricultural, Earth and Environmental Sciences, University of KwaZulu-Natal, Scottsville, Pietermaritzburg, South Africa, Centre for Water Resources Research, School of Engineering, University of KwaZulu-Natal, Scottsville, Pietermaritzburg, South Africa, Centre on Climate Change and Planetary Health, London School of Hygiene and Tropical Medicine, London, United Kingdom

• Nosipho Dlamini, 
• Aidan Senzanje, 
• Tafadzwanashe Mabhaudhi

• Published: August 26, 2024
• https://doi.org/10.1371/journal.pclm.0000464
• Reader Comments

Climate change strains the global water supplies’ capability to meet demands, especially in regions like South Africa, where resources are already scarce. The interconnectedness of water, energy, and food (WEF) exacerbates this challenge, amplifying the impact of climate change on water resource management across these sectors. Thus, in strengthening the long-term resilience and reliability of water resources, a necessity in South Africa, research on climate change and the WEF nexus is needed for water resource planning and development. Employing the WEF nexus approach, we applied the Climate Land-Use Energy and Water Strategies (CLEWS) modelling framework to assess climate change impacts on the water supply-demand relationship, considering the domestic, agriculture (irrigation) and energy generation sectors, and adopting the Buffalo River catchment, KwaZulu-Natal, South Africa, as a case study. A threefold approach was utilized: (1) water supplies and demands and the total unmet demands were quantified; (2) the percentages of water demands covered per sector were derived; and (3) the reliability of the water system to meet each sector’s water demands was computed. The findings projected slight decreases (2%) in the Buffalo River catchment’s total water demands towards the end of the 21 st century, mainly due to changes in land suitability for agriculture. While the water system is projected to be reliable for highly populated municipalities (demand coverage index > 70%; reliability index ≥ 20%), it is unreliable for sparsely populated and agriculturally intensive municipalities (demand coverage index ≤ 12%; reliability index = 0%). Such unreliability will strain agricultural production as more than 70% of irrigation water demands come from these municipalities. Nexus-smart water allocation and capacity development plans are recommended to manage these challenges and ensure a just and sustainable water supply-demand relationship in light of climate change.

Citation: Dlamini N, Senzanje A, Mabhaudhi T (2024) Modelling the water supply-demand relationship under climate change in the Buffalo River catchment, South Africa. PLOS Clim 3(8): e0000464. https://doi.org/10.1371/journal.pclm.0000464

Editor: Ahmed Kenawy, Mansoura University, EGYPT

Received: September 13, 2023; Accepted: July 30, 2024; Published: August 26, 2024

Copyright: © 2024 Dlamini et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: Additional information can be found in the Annexure Document.

Funding: This research received financial support from the National Research Fund (NRF [NRF to ND]), the Nurturing Emerging Scholars Programme (NESP [NESP to ND]) and the Water Research Commission (WRC [WRC to TM]). This work forms part of the Sustainable and Healthy Food Systems (SHEFS) Programme, supported through the Welcome Trust's Our Planet, Our Health Programme (grant number: 205200/Z/16/Z to TM). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Human activities such as agricultural production, energy generation, population growth, and socio-economic development are increasing global water demands and competition for water supplies. This presents significant risks to the reliability of water supplies to satisfy demands in light of climate change [ 1 , 2 ]. Thus, to reduce conflicts and optimize water supply and demand management, it is vital to evaluate the key factors that drive conflict in the water supply-demand relationship and consider how they could change and affect each other under climate change [ 3 – 5 ].

With the intent of identifying key factors influencing water resource management globally, a "nexus" among food, energy, and water was established at the 2008 World Economic Forum [ 6 , 7 ]. The Water-Energy-Food (WEF) nexus refers to the interconnections among water, energy and food systems [ 8 ]. Extensive research and applications of the WEF nexus approach to resource management have been conducted worldwide [ 2 , 9 ]. However, studies focusing on applying WEF nexus planning in Africa have been limited, which contributes to the approach’s delayed adoption [ 10 ]. In South Africa, numerous studies have identified the primary obstacles to cross-sectoral coordination in resource management being the widespread lack of understanding and practical cases demonstrating the implementation of the WEF nexus approach [ 11 – 14 ]. This underscores the pressing need for South Africa to adopt nexus thinking in policy formulation and planning, given the country’s ongoing struggles with water scarcity, increasing energy and food demands, and inadequate systems for climate change adaptation [ 15 , 16 ]

The Climate, Land-use, Energy, and Water Strategies (CLEWS) framework, initially proposed by the International Atomic Energy Agency, is a WEF nexus approach that integrates the climate system in the exploration and analysis of the linkages between WEF resource systems [ 17 ]. The CLEWS framework generally addresses multiple objectives, the most widespread being cross-sectoral policy assessments combined with sustainable resource management [ 18 ]. The framework has gained traction in academic, national, regional, and local policy development spheres [ 12 , 18 , 19 ].

Ramos et al . [ 18 ] reviewed the CLEWS framework’s phases and applications, highlighting key research contributions, including studies in Africa, such as (a) the 2012 CLEWS study in Mauritius assessing biofuel policy coherence [ 20 ], (b) the 2018 CLEWS investigation in Ethiopia on energy policies amid climate change and (c) the 2015 CLEWS analysis in Cape Town on energy implications of water supply expansion and land use changes [ 19 ]. Stakeholder involvement is also heavily emphasized when undertaking a CLEWS assessment to ensure scenario development aligns with development plans [ 21 ].

Most of the CLEWS assessments are devoted to assessing and developing policy recommendations from an energy viewpoint, primarily bioenergy use and electricity grid pathways, as this was the main focus of the framework’s initial development, and the basis of the CLEWS single-use Open Source Energy Modelling System (OSeMOSYS) tool [ 18 ]. While global water and energy assessment are gradually increasing, there is still a lack of land and climate change assessment utilizing the CLEWS framework [ 18 , 22 ]. This is reflected in South African CLEWS studies, which employ the framework from a water and energy perspective [ 19 , 23 , 24 ].

With over 98% of South Africa’s surface water already allocated (21), the strain on water resources is expected to worsen due to projected climate change impacts [ 25 ]. Given such, we conducted a CLEWS assessment from a South African catchment perspective, to quantify the impact of climate change on the water supply-demand relationship, considering the potential changes in land suitability for agriculture, population growth, and energy production. Using the Buffalo River catchment in the KwaZulu-Natal province, South Africa, as a case study, this study presents a prospective assessment of the catchment’s water supply system’s capacity and reliability to meet demand, to aid in strategic thinking towards integrated water resource planning and management.

The Buffalo River catchment has not been able to fulfil increasing water demands in recent years even though it is a high rainfall region receiving, on average, 802 mm/annum [ 26 ]. This water supply deficit is also expected to continue under climate change, irrespective of the anticipated rises in average rainfall and surface water availability. Dlamini et al . [ 27 ] projected increased unmet demands in the Buffalo River catchment due to climate change-induced increases in rainfall variability, yielding low temporal water storage. We find this in many regions across the world, such as the Yellow River catchment in China [ 28 ], central-eastern Mexico [ 29 ], South Asia [ 30 ], and in the south of Marrakech, Morocco [ 31 ], whereby inadequate water supply facilities and management, as well as climate change impacts, threaten to strain the water supply-demand relationship, despite the region having ample water resources to supply the population.

As it stands, the Buffalo River catchment’s water supplies have been characterised as unreliable by the local municipal authorities, which depend upon it for water, thus requiring remodelling [ 26 , 32 , 33 ]. Building on the Dlamini et al . [ 27 ] study, which projected demands from energy and irrigation to follow historical trends, the current study aims to improve this by further investigating: (a) the potential consequences of climate change on the catchment’s primary water users and (b) the reliability of water infrastructure and allocation plans to meet projected water demands. This study was based on the null hypothesis that climate change does not influence the correlation between water supply and demand. The findings offer valuable insights into the water supply-demand dynamics’ sensitivity to climate change, and key areas of intervention for addressing current and future water resource management challenges.

Materials and methods

Description of case study–buffalo river catchment.

The Buffalo River catchment forms part of the uThukela Water Management Area in northern KwaZulu-Natal, South Africa. The study area, shown in Fig 1 , has maximum coordinates of 28°42’59” South latitude and 30°38’30” East longitude [ 26 ]. The total area of the catchment is 9 803 km 2, and it covers parts of the Amajuba and uMzinyathi District Municipalities. The study area primarily provides water for irrigation, energy generation, mining, and bulk industries. The climate of the Buffalo River catchment can be described, in the South African context, as a high rainfall area, receiving on average 802 mm of rainfall per annum. Due to the intense precipitation variability, the catchment has faced drought conditions in the past years, especially during 2015 and 2016, which threatened the ability of water supplies to meet demands [ 26 ]. Therefore, the implications of possible climate change outcomes on the Buffalo River catchment’s capability to meet its water demands must be evaluated.

• PPT PowerPoint slide
• PNG larger image
• TIFF original image

The vector shapefiles were retrieved from the South African Department of Water and Sanitation ( https://www.dws.gov.za/iwqs/gis_data ) and Standford University’s online library ( https://earthworks.stanford.edu ). The map was created using ESRI’s ArcGIS Software Version 10.6.0.8321.

https://doi.org/10.1371/journal.pclm.0000464.g001

CLEWS modelling framework and tools

The modelling framework and tools used to carry out the integrated reliability assessment of the Buffalo River catchment’s water system were chosen among the available Water-Energy-Food (WEF) nexus frameworks and tools. The WEF nexus is a methodology that ‘ considers the interlinkages , synergies , harmonisation and trade-offs when managing water , energy and food resources [ 34 ]. As this study aims to investigate the implications of climate change on water systems and reliant energy and agriculture activities, the WEF nexus is ideal given that it provides a wide range of analytical tools and frameworks for understanding how WEF resources interact with one another under pressures such as climate change [ 35 ].

Analytical approaches suitable for use in South Africa that deal specifically with WEF resources management and climate change are the Climate, Land-Use, Energy and Water Strategies (CLEWS) approach and the ANEMI model. While the ANEMI model carries out an interconnected evaluation of the physical, ecological, and hydrological processes [ 12 , 36 ], the CLEWS approach can be carried out using a single model, or by soft-linking and hard-linking (mixed methods approach) different land, energy and water models under various climate scenarios. Therefore, the CLEWS mixed methods approach was selected based on its flexibility of analytical model selection for each WEF component [ 12 ].

The Long-range Energy Alternatives Planning (LEAP) model is a typical CLEWS analytical tool for energy system analysis. LEAP is an integrated, scenario-based modelling tool [ 37 ], well-fitting to this study’s intended aim of analysing the water system’s reliability under different climate change scenarios. LEAP also allows tracking energy consumption, production, and resource extraction in all sectors of the economy [ 37 ]. The Water Evaluation and Planning (WEAP) model is generally used for water system planning in CLEWS [ 38 ]. WEAP’s advantage is that it is a scalable resource planning tool that compares water supplies and demands and provides capabilities for forecasting demands [ 39 ]. The modelling of the land-use system was not set up as an integral part of this assessment. Instead, results from a global assessment made by the Food and Agricultural Organisation (FAO) and the International Institute of Applied Systems Analysis (IIASA), known as the global Agroecological Zones (gAEZ) assessment, were used [ 40 ]. Fig 2 displays the interactions between models and data flow using the CLEWS approach, forming the basis of this study’s methodology.

https://doi.org/10.1371/journal.pclm.0000464.g002

Current practice approach

The Current Practice Approach (CPA), also shown in Fig 2 , was established as the initial step of the CLEWS modelling approach. The CPA was detailed and performed by Dlamini et al . [ 27 ]. In the CPA, the WEAP model was solely used to simulate and project the effects of rainfall variability on streamflow and net surface water storage without explicitly considering the effects of changes in land use and energy systems over time. In investigating climate change impacts on surface water availability, precipitation output data from global circulation models (GCMs) based on the Representative Concentration Pathways (RCP) 4.5 and 8.5 climate change scenarios was utilised as input data to the WEAP model. The projected net surface water supply changes, i.e., surface water available after water abstractions, were compared to the historical simulated values. According to the assessments, climate change is expected to increase precipitation, leading to increased evapotranspiration and surface runoff. As the frequency of peak flooding events increases, climate change is expected to increase surface water availability through recharges of surface water storage [ 27 ]. Tables 1 and 2 summarise the CPA’s key data inputs and study findings, extracted from and explained in Dlamini et al . [ 27 ].

https://doi.org/10.1371/journal.pclm.0000464.t001

https://doi.org/10.1371/journal.pclm.0000464.t002

CLEWS approach

The RCP4.5 and RCP8.5 climate change scenarios assessed in the CPA were reassessed using the CLEWS approach, also shown in Fig 2 , to further investigate the relationship between water demands and the availability and reliability of water supply under climate change considering the following additional linkages from the water, energy and agricultural systems:

• Irrigation water requirements (IWR) are used to produce the projected agroecologically attainable yield of the catchment’s irrigated commercial crops (derived from the gAEZ land-use assessment).
• Energy demands for irrigation and household (derived using the LEAP model).
• Water demands for producing LEAP energy demands (derived from the WEAP model).

Land-use modelling.

Fig 3 summarizes the methodology used to retrieve the attainable yields and their respective irrigation water requirements for irrigated commercial farmlands in the Buffalo River catchment using the global Agro-Ecological Zones (gAEZ) assessment. The gAEZ land-use assessment relies on well-established land evaluation principles to assess natural resources for finding suitable agricultural land utilization options [ 40 ]. The results of gAEZ’s crop suitability and land productivity evaluation are stored as separate databases, each organized in terms of 5 arc-minute (about 9 x 9 km at the equator) grid cells accessed at https://gaez.fao.org [ 19 ].

https://doi.org/10.1371/journal.pclm.0000464.g003

Land classification, suitability mapping and crop summary tables.

The gAEZ assessment aimed to extract information on the catchment’s projected attainable agricultural yields and irrigation water requirements under climate change. In the Buffalo River catchment, maize, wheat, oats, soybean, and ryegrass are the most dominant irrigated crops. Therefore, the study employed these crops in the analysis of irrigated agriculture. Sprinkler-irrigated commercial farmlands were chosen due to a lack of data in the assessment regarding forecasts of irrigated subsistence farmlands and other types of irrigation systems.

Historical and projected crop suitability classification maps were extracted and analysed using the ArcGIS software. It is important to note that the gAEZ assessment’s historical suitability maps were created based on the CRUT32 model output data from 1981 to 2010, and projected suitability maps used numerous GCMs detailed in Fischer et al . [ 40 ]. To maintain consistency in projections, suitability maps produced using MIROC-ESM-CHEM and NorESM1-M climate models were considered based on these GCMs outputs included in the precipitation projection analysis (see Table 1 ). After assigning each local municipality in the Buffalo River catchment with a suitability class per crop type described using Table 3 , crop summary tables were used to determine the agro-ecological attainable yield per crop type, alongside the net irrigation requirements, to obtain the yield.

https://doi.org/10.1371/journal.pclm.0000464.t003

Bias correction.

The agricultural production and land statistics presented in crop summary tables are at a national scale. Hence, Fischer et al . [ 40 ] suggested downscaling outputs when aggregating national production statistics to individual spatial units. Therefore, the projected attainable yields were bias-corrected using the linear scaling (LS) equation presented in Eq ( 1 ), as it maintains the observed parameter’s average [ 41 ]. The bias correction process used records of irrigated commercial crop production yields in the Buffalo River catchment, obtained from StatsSA [ 42 ] (see S1 Fig – S3 Fig in the Annexure). The same bias correction methodology was applied to the irrigation water requirement projections.

CY raw = raw crop yield data (kg/ha)

Energy modelling.

The modelling of the energy demands was achieved using the Long-range Energy Alternatives Planning (LEAP) model, version 2020.1.0.69, developed by the Stockholm Environment Institute (SEI) [ 43 , 44 ]. The analysis covers irrigation and household energy demands, as seen in Fig 4 , in each local municipality within the Buffalo River catchment.

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Changes in irrigated areas.

The water use efficiency parameter (WUE), defined as the ratio of crop yield to applied water [ 45 ], was utilised to compute the projected changes in irrigated field sizes (ha) using Eqs ( 2 ) and ( 3 ) [ 46 ]. Each crop type’s historical WUE was computed using irrigated crop yield data from StatsSA [ 42 ] and irrigation water requirements from Stevens et al . [ 47 ] and DAFF [ 48 ] (see S1 Table in the Annexure) and kept constant throughout the study period. Employing the gAEZ’s projected attainable yield and irrigation water requirements, the projected irrigated areas were calculated using Eq ( 3 ) [ 46 , 49 ].

CY = Crop yield (kg/ha), and

IWR = Irrigation water requirements (mm/ha)

CY new = Projected crop yield (kg/ha),

IWR new = Projected irrigation water requirements (mm/ha/(season))

Computing power requirements for irrigation.

As per the gAEZ assessment, only sprinkler irrigation was considered for irrigation energy consumption. The power requirements per crop type per hectare (P) were calculated using Eq ( 4 ) [ 49 , 50 ].

C e = annual energy cost to operate centre pivots (R/ha/year),

En c = energy rates (R/kWh).

In computing the historical energy rates ( En c ) values shown in Fig 5 , the average Eskom rates for rural/farming users in Rands per kilowatt-hour (R/kWh) were obtained from Eskom’s annual reports (ESKOM [ 51 ]). According to Venter et al . [ 52 ], approximately 80% of registered irrigation systems in South Africa are pressurized types, which include centre pivots, sprinklers, drip and micro-sprinkler systems, and commercial farmers tend to be more favourable towards centre pivots [ 53 ]. As irrigated commercial farmlands are considered in this study, it was assumed that all irrigation in the catchment is conducted using centre pivots.

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For the annual energy cost to operate centre pivots ( C e ), the values are the sum of fixed and variable electricity costs [ 49 , 50 ]. Fixed electricity costs are constant and can only be changed by the electricity supplier, Eskom [ 52 ]. The variable electricity costs are due to irrigation hours, kilowatt (kW) requirements and the electricity tariff. A study conducted by Venter et al . [ 52 ], compared the total electricity costs of operating a small (30.1 ha) and large (47.7 ha) centre pivot under the 2018 Landrate and Ruraflex electricity tariffs at different system delivery capacities (see Table 4 ), and found that Ruraflex is more profitable than Landrate irrespective of the centre pivot size and irrigation system delivery capacities. Thus, the Ruraflex electricity tariffs were used in this study.

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As Eskom introduced the Ruraflex electricity tariff in 2003, its tariff growth rates since then have been utilized to interpolate the variable electricity costs based on the 2018 value in Table 4 . C e value of the large centre pivot with a system delivery capacity of 8 mm/day was deployed in this study since it was the most profitable system. The Ruraflex tariffs were obtained from ESKOM [ 51 ]. From 1990 to 2003, due to insufficient available records, it was assumed that the variable electricity costs’ growth rates were the En c rates. Fig 5 displays the growth trends of C e under the historical period; these trends were duplicated throughout the study period.

Household electricity consumption.

Before computing household electricity consumption, data related to the number of households and settlement types in each local municipality in the Buffalo River catchment was gathered, as seen in Table 5 . Due to South Africa having higher electrification rates in urban households than rural households [ 54 ], and the Amajuba district municipality, which covers the Newcastle, Dannhauser and Utrecht local municipalities, having its bulk electricity infrastructure concentrated in urban areas [ 55 ], urban households were assumed to be fully electrified. The rural households were divided into electrified and non-electrified; for the study, the non-electrified rural households were not considered. For electrified households, data from StatsSA [ 56 ] on the percentage of households having access to the following energy services was also collected, which is only available for 2015: cooking, lighting, water heating, space heating, and refrigeration (see S4 Fig to S8 Fig in the Annexure).

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The Buffalo River catchment’s local municipalities’ households were classified, employing the incomes in Fig 6 , into income groups using the following categories: low-income households make less than R86 000 per year (pa), middle-income households make between R86 001 pa and R1 480 000 pa, and high-income households make more than R1 480 001 pa (30). From the classification, the Buffalo River catchment’s local municipalities were found to be predominantly low-income households. Using the South African energy intensity/consumption of electric appliances per household quantified in a recent study by Dinkwanyane et al . [ 64 ] for low-income groups ( S2 Table in the Annexure), the household electricity consumption was modelled using the LEAP model. Eq ( 5 ) briefly describes the LEAP modelling process using the above data.

E i ( x ) = energy intensity of energy service (x) (kWh/household) [ 64 ]

HH = Number of households in rural and urban areas with access to energy service

Household incomes per annum of the (a) Newcastle local municipality [ 59 ], (b) Utrecht local municipality [ 60 ], (c) Nquthu local municipality [ 62 ] and (d) Dannhauser local municipality [ 61 ].

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The National Energy Efficiency Strategy (NEES) target of 10% residential energy efficiency improvement by 2015 relative to a baseline projected from 2000 [ 65 ] was adopted in quantifying the changes in the energy efficiency of household appliances and energy services from 1990 to 2014, and 2016 to 2099, by assuming a 10% energy efficiency improvement every 15 years.

Model interactions and data analysis statistics.

After quantifying energy use by irrigation and households (MWh/annum), they were manually transferred into the WEAP model, as observed in the methodology’s flow chart shown in Fig 2 . Since the LEAP model cannot simulate the water requirements for energy generation per kWh, a value of 1100 litre/MWh, which is the average water use of the Majuba power station [ 66 ], was computed as the annual water use rate for energy generation. As a result, the WEAP model simulated and projected the total water supply requirements, considering the variations in household, irrigation, and energy generation requirements.

As the WEAP model is the central model in this assessment, it was calibrated against historical streamflow observations for the period 01/01/1990 to 31/12/2019. The calibration and validation processes, including data used, the respective sources and outcomes, are detailed in the Dlamini et al . [ 27 ] study and presented in Table 6 , therefore they are not repeated in this current study. Descriptive statistics (means, percent increases relative to the historical scenario and coefficients of variation) were employed to analyse the output of the WEAP, LEAP and gAEZ models.

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Results and discussion

As discussed in the previous sections, results from the CPA are detailed in the Dlamini et al . [ 27 ] study and are summarized in the Current Practice Approach section of this study. It should be stated that, because the computational methods and input data used are the same, the historical and projected values of precipitation, evapotranspiration, and household water demands’ values under the CPA and CLEWS approaches are consistent. Hence, the water systems outputs (surface runoff and water availability) established under the different computations of energy and irrigation water demands using the CLEWS approach are compared to those established under the CPA to see if the CLEWS modelling approach brings upon any significant differences. Furthermore, the demand site coverage and water supply system’s reliability results under both CPA and CLEWS, which are the focus of the current paper, are presented and compared in this section.

Surface runoff

The surface runoff at the Buffalo River’s outlet ( Q ) projected from the CPA and CLEWS approaches displays differences throughout the 21 st century. CLEWS projected Q values, which are, on average, 8.5% lower than those projected by the CPA approach under both climate scenarios, thus flagging increased water usage and/or storage within the water supply system. Nonetheless, as seen in Table 7 , average Q volumes are still anticipated to increase under CLEWS for both RCP4.5 and RCP8.5 climate change scenarios. The projected increase in Q reflects the expected rainfall increases throughout the study period. This finding agrees with the results of Ndlovu et al . [ 68 ], who projected increased surface runoff in the KwaZulu-Natal province, South Africa, due to increased extreme rainfall events, i.e., days with 20 mm or more precipitation. A review undertaken by Kusangaya et al . [ 69 ] highlights that a general decrease in runoff is expected in Southern Africa; however, in high-rainfall regions like the uThukela River catchment, where the Buffalo River catchment is located, Kusangaya et al . [ 69 ] also mentioned that increases in surface runoff are to be expected. Likewise, in the high-rainfall Kabompo River basin, Zambia, Ndhlovu and Woyessa [ 70 ] also projected increased runoff by 5% and 6% under RCP4.5 and RCP8.5, respectively.

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Water demands

Irrigation water requirements..

When compared to the CPA’s irrigation water requirements per hectare (IWR/ha), which were assumed equivalent to the historical IWR/ha values, projections of IWR/ha using the CLEWS gAEZ approach increase on average by 30% throughout the 21 st century, as seen in Fig 7 . These results are expected given that several studies investigating IWR in South African catchments [ 71 – 73 ] have presented increasing trends under climate change due to increased crop water requirements from temperature increases and changing rainfall patterns.

Historical and projected (near-, mid- and far future) irrigated areas and irrigation water requirements of ryegrass, soybean, oats and maize in the Buffalo River catchment, derived using the food and agriculture organization’s global agro-ecological zones assessment ( https://gaez.fao.org/ ) under (a) RCP4.5 and (b) RCP8.5 climate change scenarios.

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However, the suitable hectares (ha) for irrigated crop production projected by the gAEZ assessment, also shown in Fig 7 , show a declining trend under both RCP4.5 and RCP8.5 scenarios by an average of -0.4%, especially maize and soybean, which is attributable to the projected increased extreme rainfall events. These findings have been reported in several studies worldwide [ 74 – 77 ]. Irrigation generally reduces the negative effects of temperature changes [ 78 , 79 ] thus, unlike rainfed crops, land suitability for irrigated crop production is more sensitive to water availability changes brought upon by increased precipitation fluctuations and/or decreases in average rainfall [ 78 ]. Similarly, a study conducted in sub-Saharan Africa by Chapman et al . [ 80 ] also established that while precipitation increases projected by climate models indicated increased suitability for maize and soybean, a significant reduction in crop suitability is noted when climate projections consist of a high frequency of extreme rainfall events.

As a result of the decreases in irrigated crop suitability in our study, the total volume of IWR projected using the CLEWS approach, in comparison to the CPA approaches results, are lower by 17% and 19% in the mid-and far future under RCP4.5, and lower by 16% and 12% for the above-mentioned periods under RCP8.5, respectively. These results are unexpected given the previously discussed increases in IWR/ha and the consensus that irrigated agriculture is likely to strain water resources in South Africa further [ 81 ]. However, unlike the Buffalo River catchment, regional climate change projections in South Africa show slight decreases to no changes in rainfall averages and extreme events [ 82 ], which could be why irrigated agriculture is generally expected to increase. As much as the reduction in total IWR will ease the pressure on the water supply system in the Buffalo River catchment, the decreases in land suitability for crop production indicate looming food security issues.

Energy generation water demands.

From Fig 8 , the household energy demands projected using the CLEWS approach are anticipated to increase under climate change. The Newcastle local municipality contributed the most to this expected increase (0.36 million MWh/annum in 1990 to 1.25 million MWh/annum in 2099), attributable to its large and fast-growing population. Irrigation energy demands increased to 2 million MWh in 2099 under both climate scenarios, mainly due to the Nquthu local municipality’s agricultural production (see S9 Fig to S12 Fig in the Annexure). Fluctuations of the irrigation energy demands significantly impact total energy demand variations. To support this observation, the coefficient of determination ( R 2 ), which indicates the degree of similarity between observed and simulated data [ 83 ], was calculated for household and irrigation energy demands against total energy demands and found to be 0.993 and 0.987, respectively, with the R 2 plots in S13 Fig in the Annexure.

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The CPA method only considered the Majuba power station’s water demands for energy generation. As such, the Zaaihoek Water Transfer Scheme’s 3 m 3 /second transfer to the Majuba power station, equating to 27 Mm 3 /annum of the catchment’s water supply, was dedicated to power generation. In the CLEWS approach, when supplementing this demand with water required to generate household and irrigation energy, water requirements for total energy generation increase to a maximum of 28.5 Mm 3 /annum at the end of the 21 st century. Such minimal water demands from the energy sector are anticipated as energy generation in South Africa consumes approximately 5% (inclusive of coal mining) of the total water supply [ 84 ].

Total water demands.

The results on the projected CPA and CLEWS RCP4.5 and RCP8.5 total water supply requirements presented a notable gap, as seen in Table 8 , caused by the IWR results. After the incorporation of changes in attainable agricultural yields and their respective reduced overall IWR, a consequential reduction of the CLEWS total water supply requirements resulted. This is also in line with the national statistics of water use by sectors, which indicate that agriculture and irrigation are largely responsible for, and influence the trends of, water resource consumption in South Africa [ 85 ].

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Reservoir storage changes and unmet demands

The net reservoir storage ( S N ) projected under CLEWS is similar to those modelled using the CPA approach, as per Fig 9 , with mean values of 275 Mm 3 /annum (standard deviation is 37.8) and 268 Mm 3 /annum (standard deviation is 36.4) under RCP4.5 and RCP8.5 scenarios, respectively. Such results are expected as no changes were made to the reservoir operational rules in the CLEWS approach.

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In addition, for both CPA and CLEWS, the variability of projected S N values under both RCP4.5 and RCP8.5 scenarios show increases, especially in the mid-and far-future by 6% to 10%, respectively. Given the projected surface runoff ( Q ) increases of, on average, 14% per annum in the mid- and far-future timeframes, the above-mentioned increases in S N are low. This inadequate capture and storage of water supplies are assumed to be caused by water storage capacity restrictions. Thus, this observation emphasizes that the Buffalo River catchment’s water infrastructure substantially limits water supply improvements, rather than the effects of climate change, which provide an opportunity for boosting water supply. These findings are dissimilar to Strydom et al . [ 86 ] projections of reduced rainfall and streamflow in the uMgeni catchment, KwaZulu-Natal, South Africa, propelling reduced available stored water. However, in their finding, Strydom et al . [ 86 ] also highlighted that the uMgeni catchment’s reservoir operating rules are highly likely to strain water capture and storage under climate change.

Even though the projected S N values are similar in both CPA and CLEWS approaches, CLEWS’ projected unmet demands are lower by 9% and 16% in the mid- and far-future timeframes, respectively. The lower unmet demands simulated using CLEWS correspond to the anticipated declines in total IWR and in the mid- and far-future timeframes, which decreases total water requirements to be met.

Demand site coverage

The demand site coverage ( Dcov(%) ), defined as the percentage of demands met per demand site, was analysed for local municipalities as they are the primary demand sites, i.e., water is ultimately transmitted to them for domestic, energy and agricultural purposes. From Fig 10 , the annual Dcov(%) for each local municipality are different, this being a result of the water allocation plans of the Buffalo River catchment’s water supply system.

Annual demand site coverage (%) of the following local municipalities in the Buffalo River catchment: (a) Newcastle (range = 67% to 100%), (b) Dannhauser (range = 80% to 100%), (c) Nquthu (range = 8% to 11%) and (d) Utrecht (range = 9.5% to 12.5%), under the RCP4.5 and RCP8.5 climate scenarios, established using the CPA and CLEWS approaches, for the period 01/01/1990–31/12/2099.

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Historical demand site coverage.

The Newcastle and Dannhauser local municipalities’ demands are highly prioritized regarding water distribution, with simulated mean historical Dcov(%) values being 96% and 99%, respectively. However, the Utrecht and Nquthu local municipalities’ historical maximum Dcov(%) being 7% and 11%, respectively, indicates a relatively low prioritisation of these local municipalities’ water demands by the current water allocation plans. This issue of water supply provision being better in urban areas than in rural communities has been noted to be a plague within southern African regions [ 87 ]. In Zambia, rural areas similarly have more than 70% lower odds of meeting their water demands than urban areas [ 88 ].

Differences between demand site coverage projected by CPA and CLEWS.

When the Dcov(%) values projected by the CPA and CLEWS approaches are contrasted, the CLEWS Dcov(%) is significantly higher in the Dannhauser and Newcastle local municipalities, particularly in the Newcastle local municipality; in the mid- and far-future timeframes, CLEWS Dcov(%) for Newcastle is higher by 5% and 10%, respectively. Therefore, this further proves that the Buffalo River catchment’s water system’s functionality and allocation plans are centred around meeting the water demands of the Newcastle and Dannhauser local municipalities, making them high-priority demand sites, and enabling these sites to maintain a Dcov(%) above 70%, even under worsened climate change conditions. The domestic and energy sectors benefit substantially from this as a minimum of 76% of their water requirements emanate from high-priority demand areas, thus yielding a maximum of 30% of their water demands not being met under climate change.

For the Nquthu and Utrecht local municipalities, Dcov(%) remains below 12% under climate change, reinforcing that these are low-priority water supply regions. With over 65% of the agricultural sector’s water demands stemming from these low-priority regions, it is expected that an average of 90% of irrigation water demands in these regions will not be met, equating to approximately 60% and 65% of the catchment’s total IWR not being met under the RCP4.5 and RCP8.5 scenarios, respectively. Similar results are highlighted in a study by Nhemachena et al . [ 89 ], who stated that water scarcity, increased demand, and competition from other water users will reduce agricultural productivity by 50% or more in South African regions, as well as other western parts of southern Africa including Botswana, Namibia, and Zambia, by 2080.

Differences in projected water demand coverage for RCP4.5 and RCP8.5 scenarios.

To check for significant differences in the CLEWS Dcov(%) under the RCP4.5 and RCP8.5 scenarios, the local municipalities’ Dcov(%) outputs were analysed with the statistical Welch test for parametric t-tests and the Mann-Whitney test for non-parametric t-tests [ 90 ], upon verification of normality using the Shapiro-Wilks test [ 91 ]. Moreover, the significance level ( α ) for the t-tests was set at 5% to ensure that, in cases where the significance level has been surpassed, the null hypothesis (no difference in means) is rejected. The results are tabulated in Tables 9 and 10 .

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From Table 10 , the differences in Dcov(%) values are only significant in the near- and far-future timeframes, with the differences in the mean Dcov(%) values (RCP4.5 mean value–RCP8.5 mean value) per local municipality range from -0.02 to -0.84 in the near future, and -0.21 to -3.91 in the far-future. This highlights that under the RCP8.5 scenario, the water demands that can be covered in each local municipality are expected to be lower than those anticipated under the RCP4.5 scenario, hence flagging concerns related to the reliability of the water supplies during these timeframes.

Reliability of water system

T = total number of years of respective timeframe

T D = total number of years where demand site Dcov(%) ≠ 100%

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Demand sites that yielded high RE(%) of over 50% include the Majuba power station, Biggarsberg WTP, Isandlwana WTP, Ngagane WTP and the Vant’s Drift WTP. The Majuba power station is the only demand source extracting water from the Zaaihoek Water Transfer scheme via the Zaaihoek Dam, located in the upper regions of the Buffalo River catchment. As such, this provides a reason for the high RE(%) . The Biggarsberg, Isandlwana, Ngagane and Vant’s Drift WTPs’ first supply preferences are primary demand sites, and as such, their demands for transmission are met first, hence their high RE(%) values. To elaborate, the Qudeni WTP is a secondary supply preference for the Nquthu local municipality, whereas the Vant’s Drift WTP is the primary supply preference, which is why Qudeni’s RE(%) value is 0% while Vant’s Drift is 93%.

In noting the impacts of climate change on RE(%) , an average reduction of 2% and 4% is noted when comparing the historical RE(%) to that of the CLEWS under the RCP4.5 and RCP8.5 scenarios, respectively. This decline in reliability under climate change is unexpected given the reduced water demands, and it is assumed to be resulting from the increased frequency of extreme rainfall events, which also alter the temporal surface water storage and supply in the same pattern. Given this, it is evident that the relationship between water supply is affected by temporal climatic changes, as reported in several studies across the globe; for example, in Morocco’s Middle Draa Valley and Cambodia’s Tonle Sap Lake, drought conditions are anticipated under climate change and are consequently predicted to alter water storage and increase the gap between water supply and demand [ 93 , 94 ]. Similar to our study’s findings, the Pozzillo Reservoir in Sicily, Italy, is anticipated to experience increased rainfall under climate change; however, despite these increases, reductions in reservoir temporal reliability are projected, especially under the RCP8.5 scenario, as a result of increased frequency of extreme weather events, thus aggravating increases in water supply deficit [ 95 ].

When comparing the primary demand sites’ RE(%) values, the Newcastle and Dannhauser local municipalities’ RE(%) decreases by 3% under the CLEWS approach and climate change conditions. However, the RE(%) remains above 20%. This is owing to them being high-priority sites and having multiple supply points, which increases the stability of their RE(%) . The increases in Dcov(%) for the Nquthu and Utrecht local municipalities, however, proved to be insignificant as their CLEWS RE(%) values are 0%, i.e., their annual water demands are projected not to be fully supplied throughout the projection period, i.e., Dcov(%) ≠ 100%. Therefore, these results similarly demonstrate the sentiments echoed in the demand site coverage section, indicating that the correlation between water supply and demand in domestic and energy sectors is notably stronger compared to the food (agricultural) sector. Given this poor demand coverage and the unreliability of water supplies to meet demands from the agricultural sector, this highlights and supports the statement made by Simpson et al . [ 10 ] on the limited integration of WEF nexus principles into current WEF resource management strategies in South Africa.

Several studies have also flagged the inadequate supply of agricultural water demands multiple climate change scenarios [ 3 , 7 , 96 – 98 ] and propose implementing measures to enhance the resilience of agricultural systems, such as promoting water-efficient eco-friendly farming practices, managing water pollution, and increasing biodiversity through crop rotation and revegetation efforts. In addition to these interventions, it is imperative for future planning and management of water resources to extend beyond the water-energy nexus thinking. For the Buffalo River catchment, this involves enhancing water storage capacities, capitalizing on the expected increase in surface runoff due to climate variations, and improving water allocation to optimize agricultural productivity, particularly for crops like maize and soybean.

Study limitations

The modelling approach’s limitations include the use of statistically downscaled (SD) climate change projections were used. The computation of SD projections is heavily based on the observed relationship between large-scale atmospheric variables and local or regional climate variables. Due to the Earth’s system being nonlinear, a statistical relationship that was held in the past may not apply in the future. Thus, SD methods not accounting for natural climate fluctuations could cause non-representative results in climate projections. Additionally, data limitations enabled only surface water and the primary water consumers in the catchment (household, irrigation, and energy production) to be accounted for. Therefore, there is a possibility of error in the quantified water supply-demand relationship. Despite these potential limitations, the model validation process produced satisfactory results.

Conclusions and recommendations

Understanding the effects of climate change on water, energy, and food resources is crucial for developing sustainable water management policies, given the interconnectedness of these resources. Therefore, this study successfully employed the CLEWS modelling framework, incorporating tools like WEAP, LEAP, and gAEZ, to evaluate how climate change impacts the balance between water supply and demand across domestic, energy, and agricultural (irrigation) sectors in the Buffalo River catchment, KwaZulu-Natal, South Africa. The findings contribute to South Africa’s dearth of knowledge on the WEF nexus and illustrate how WEF nexus thinking can be applied to water resource management in South African catchments.

This study was premised on the null hypothesis of climate change not influencing the relationship between water supplies and demands. However, in conclusion, we reject the null hypothesis. The following shifts in key factors (sectors) influencing water demands and supplies in the Buffalo River catchment are anticipated under climate change:

• Increased surface water storage is anticipated under climate change due to increased surface runoff. However, this surface water supply increase is expected to be negligible, primarily due to the constraints posed by insufficient water storage infrastructure and the catchment’s water distribution plans.
• Land suitability for agricultural production is expected to decrease under climate change in the Buffalo River catchment, thus propelling the summative values of irrigation water demands also to decline.
• Increased water demands from domestic and energy generation were projected under climate change. However, the decline in irrigation water requirements poses a significantly greater influence on the total water requirements of the Buffalo River catchment—the overall decline of the total requirements observes this.

Due to the expected increased rainfall variability in the Buffalo River catchment, the capability and reliability of the water supplies to meet demands are anticipated to decline under climate change as we tend towards the end of the 21 st century, despite the above-mentioned expected increases in water supply and decreases in total water demands. With domestic and energy-intensive sites (Newcastle and Dannhauser local municipalities) being high-priority for water supply, the low-priority regions with extensive agricultural production (Nquthu and Utrecht local municipalities) are primarily affected by this decline in water supply reliability. The inequality in water supply distribution, propelled by the reduced land suitability for crop production under climate change, poses a critical concern for food security and the socioeconomic standing of the catchment communities. Moreover, if not curtailed, the anticipated decline in water resource reliability could perpetuate unsustainable water management practices, prompting individuals to extract and utilise untreated water sources. This not only deteriorates water resources but also increases the risk of water-related health concerns.

In essence, our research findings highlight that the balance between water supply and demand is highly sensitive to climate change and resource management. Thus, improving the relationship between water supply and demand under climate change entails strengthening water infrastructure reliability and allocation plans. In doing so, it is advisable to consider water supply infrastructure as a service rather than merely a facility. Thus, future water resource plans should not focus only on expanding water storage but also on optimizing the provision rate by adjusting water transmission and diversions during periods of system failure, especially in low-priority regions. This can be executed by redirecting some water transmission links from the high-priority demand sites to Utrecht and Nquthu and re-establishing the operational rules of WTPs, especially the Utrecht WTP.

The effectiveness of both the WEAP and LEAP models hinges on the quantity and detail of the data they utilize. Therefore, it is strongly recommended that future research uses high-quality data in these models’ simulation processes. This includes, for example, employing dynamically downscaled precipitation projections, which offer higher resolution compared to statistically downscaled data, and incorporating the latest CMIP6 GCM climate output data. However, it is worth noting that the bias-correction method employed in deriving precipitation estimates from the statistically downscaled data, as evidenced by the WEAP model performance evaluation, provided adequate precipitation values that accurately reflected the hydrology of the catchment area.

Since this study is limited by the exclusion of groundwater as a water source, it is suggested that future research should concentrate on gathering detailed quantitative data on groundwater availability, consumption patterns, and energy usage for household and irrigation purposes within the Buffalo River catchment. Given the significance of groundwater utilization in climate change adaptation, incorporating groundwater data would enable the conjunctive use of both ground and surface water resources, thereby enhancing the overall understanding and management of water resources in the catchment area.

The CLEWS framework effectively illustrates the intricate relationships among the Buffalo River catchment’s water, energy, and food resources. Therefore, due to its dynamic structure, the use of this framework is encouraged for studies investigating the impacts of climate change on the WEF resources and other sectors as well such as health, environment and biodiversity, termed the “WEF+” nexus, given that the incorporation of the other sectors is done in a scientifically sound manner. The study’s results can serve as valuable reference points for future research on the climate change-water-energy-food nexus, enabling policymakers and decision-makers better to understand climate change’s effects on these resources and evaluate the sustainability of current water and catchment management plans in light of climate change.

Supporting information

S1 table. irrigation water requirements for each dominant crop grown in the buffalo river catchment [ 47 , 48 ]..

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S2 Table. Average energy consumption of electric appliance/energy service in kWh per income group for the year 2015 [ 64 ].

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S1 Fig. Planted hectares in the Buffalo River catchment’s local municipalities [ 42 ].

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S2 Fig. Irrigated commercial crop production yields in the Buffalo River catchment’s local municipalities (kg/ha) [ 42 ].

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S3 Fig. Thus figure shows the production in kg/ha of commercial crops in the Buffalo River catchment’s local municipalities [ 42 ].

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S4 Fig. Households by main source of energy for cooking [ 56 ].

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S5 Fig. Households by main source of energy for heating(refrigeration) [ 56 ].

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S6 Fig. Households by main source of energy for lighting [ 56 ].

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S7 Fig. Households by main source of energy for water heating [ 56 ].

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S8 Fig. Households by main source of energy for space heating [ 56 ].

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S9 Fig. gAEZ projected irrigated area per local municipality under RCP 4.5 scenario.

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S10 Fig. gAEZ projected irrigated area per local municipality under RCP 8.5 scenario.

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S11 Fig. LEAP irrigation energy demands (MWh/annum) per local municipality in the Buffalo River catchment under the RCP4.5 scenario.

https://doi.org/10.1371/journal.pclm.0000464.s013

S12 Fig. LEAP irrigation energy demands (MWh/annum) per local municipality in the Buffalo River catchment under the RCP8.5 scenario.

https://doi.org/10.1371/journal.pclm.0000464.s014

S13 Fig. Comparison of irrigation energy demands, and the total energy demands throughout the projection period (01/01/2020–31/12/2099) under the (a) RCP4.5 scenario and (b) RCP 8.5 scenario.

https://doi.org/10.1371/journal.pclm.0000464.s015

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