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Modelling the water supply-demand relationship under climate change in the Buffalo River catchment, South Africa [1]

['Nosipho Dlamini', 'Bioresources Engineering Programme', 'School Of Engineering', 'University Of Kwazulu-Natal', 'Scottsville', 'Pietermaritzburg', 'South Africa', 'Centre Of Transformative Agricultural', 'Food Systems', 'School Of Agricultural']

Date: 2024-09

Abstract 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 21st 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.

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 21st 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.

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[1] Url: https://journals.plos.org/climate/article?id=10.1371/journal.pclm.0000464

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