Editing IPCC:AR6/WGII/Chapter-9 (section)

=== 9.7.3 Water Adaptation Options and Their Feasibility ===

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==== 9.7.3.1 Reducing Risk Through a Systems Approach to Water Resources Planning and Management ====

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An integrated systems and risk-based approach to the design and management of water resources at scale is generally accepted as a practical and viable way of underpinning the resilience of water systems to climate change and human pressures ( [[#Duffy--2012|Duffy, 2012]] ; [[#García--2014|García et al., 2014]] ). Such approaches confer multiple benefits to nature and society at scale and enhance efficiency gains through technology and management improvements, but their full implementation has not yet been realised ( [[#Weinzierl--2013|Weinzierl and Schilling, 2013]] ; [[#McDonald--2014|McDonald et al., 2014]] ; [[#UN%20Environment--2019|UN Environment, 2019]] ). Drylands are particularly singled out as ignored areas that require integrated water resource management approaches ( [[#9.3.1|Section 9.3.1]] ; [[#Stringer--2021|Stringer et al., 2021]] ). Appropriate ecosystem-based adaptations that are applicable at scale should be identified and strongly embedded in these approaches to deliver multiple benefits while maintaining the integrity of ecosystems and biodiversity ( [[#UN%20Environment--2019|UN Environment, 2019]] ; see Sections 9.6.4; 9.8.5; Box 4.6). Furthermore, adaptation options are often influenced or constrained by institutions, regulation, availability, distribution, price and technologies ( [[#McCarl--2016|McCarl et al., 2016]] ). Thus, institutional capacity to manage complex water supply systems under rapidly increasing demand and climate change stress is critical in achieving water security for African cities, particularly as cities become more dependent on alternative and distant water sources ( [[#Padowski--2016|Padowski et al., 2016]] ).

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==== 9.7.3.2 Adopting Nexus Lenses ====

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The water–energy–food (WEF) nexus explicitly recognises the strong interdependencies of these three sectors and their high levels of exposure to climate change ( [[#Zografos--2014|Zografos et al., 2014]] ; [[#Dottori--2018|Dottori et al., 2018]] ; see Box 9.5). With increasing societal demands on more variable water resources under climate change, an intensification of WEF competition and trade-offs are projected ( [[#D’Odorico--2018|D’Odorico et al., 2018]] ; [[#Dottori--2018|Dottori et al., 2018]] ). Other interacting factors, for example, the increasing number of transnational investments in land resources can lead to localised increased competition for water resources ( [[#Messerli--2014|Messerli et al., 2014]] ; [[#Breu--2016|Breu et al., 2016]] ; [[#Chiarelli--2016|Chiarelli et al., 2016]] ). Understanding such nexus interlinkages can help characterise risks to water resource security, identify co-benefits and clarify the range of multi-sectoral actors involved in and affected by development decisions ( [[#Kyriakarakos--2020|Kyriakarakos et al., 2020]] ). Major barriers and entry points for greater integration include coordination of horizontal policy and integration of climate change adaptation actions ( [[#England--2018|England et al., 2018]] ), capturing the scarcity values of water and energy embedded in food/energy products ( [[#Allan--2015|Allan et al., 2015]] ), and inclusion of community-based organisations such as water resource user associations ( [[#Villamayor-Tomas--2015|Villamayor-Tomas et al., 2015]] ) and agricultural cooperatives ( [[#Kyriakarakos--2020|Kyriakarakos et al., 2020]] ).

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==== 9.7.3.3 Climate-proofing Water Infrastructure ====

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While natural variability in the hydrological cycle has always been considered by water resources planners and engineers ( [[#Müller%20Schmied--2016|Müller Schmied et al., 2016]] ; [[#Muller--2018|Muller, 2018]] ), many countries will have to take into consideration the range of historically unprecedented extremes expected in the future. Increasingly, the provision of urban water security is dependent on the functioning of complex bulk water infrastructure systems consisting of dams, inter-basin transfers, pipelines, pump stations, water treatment plants and distribution networks ( [[#McDonald--2014|McDonald et al., 2014]] ). Risk-based studies on the potential climate change risks for water security show that there are benefits when risks are reduced at the tails of the distribution—floods and droughts—even if there is little benefit in terms of changes in the mean ( [[#Arndt--2019|Arndt et al., 2019]] ). When risk is taken into account in an integrated (national) bulk water infrastructure supply system, the overall impact of climate change on the average availability of water to meet current and future demands is significantly reduced ( [[#Cullis--2015|Cullis et al., 2015]] ). Further, stemming leakages and enhancing efficiency through technology and management improvements is important in building climate-resilient water conveyance systems ( [[#UN%20Environment--2019|UN Environment, 2019]] ). African cities could leap-frog through the development phases to achieve a water sensitive city ideal, reaping benefits such as improved liveability, reduced flooding impacts, safe water and overall lower net energy requirements and avoid making the mistakes developed countries’ cities have made ( [[#Fisher-Jeffes--2017|Fisher-Jeffes et al., 2017]] ) ( [[#Brodnik--2018|Brodnik et al., 2018]] ). However, the challenge of large proportions of the population lacking access to even basic water supply and sanitation infrastructure ( [[#Armitage--2014|Armitage et al., 2014]] ) must be simultaneously and effectively addressed, particularly in light of other major exacerbating factors, like the COVID-19 pandemic ( [[#9.11.5|Section 9.11.5]] ).

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==== 9.7.3.4 Decision Support Tools for Managing Complex Water Systems ====

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Many studies in Africa use the river basin as a unit of analysis at scale and adopt sophisticated model-based techniques to assess climate change impacts on hydrology under different climate and development scenarios, thereby presenting trade-offs between competing uses such as hydropower generation, irrigation and ecosystem requirements ( [[#9.12.1|Section 9.12.1]] ; [[#Yang--2018|Yang and Wi, 2018]] ; [[#Ahmed--2020|Ahmed, 2020]] ). However, longer (multi-decadal) hydrological datasets and model improvements are required ( [[#Taye--2015|Taye et al., 2015]] ), and models should incorporate the quantification of the wider benefits, risks and political opportunities arising from reservoir development to better inform decision makers to achieve a higher level of (transboundary) cooperation ( [[#Digna--2016|Digna et al., 2016]] ; [[#Nijsten--2018|Nijsten et al., 2018]] ). Collaboration between scientists and policymakers to address the complexity of decision making under uncertainty ( [[#Steynor--2016|Steynor et al., 2016]] ) ( [[#Pienaar--2017|Pienaar and Hughes, 2017]] ), coupled with community involvement in participatory scenario development and participatory GIS to aid in collaborative planning that is context specific ( [[#Muhati--2018|Muhati et al., 2018]] ; [[#Álvarez%20Larrain--2019|Álvarez Larrain and McCall, 2019]] ) are powerful tools for more beneficial adaptive and resilience-building actions.

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==== 9.7.3.5 Other Adaptation Options ====

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Climate change is projected to increase dependence upon groundwater withdrawals in most parts of Africa as an adaptive strategy to amplified variability in precipitation and surface water resources, highlighting the need for conjunctive surface-groundwater management and rainwater harvesting ( [[#Cobbing--2019|Cobbing and Hiller, 2019]] ; [[#Taylor--2019|Taylor et al., 2019]] ). Alternative water supply options such as desalination, managed aquifer recharge, stormwater harvesting and re-use (direct and indirect, potable and non-potable), all require significant amounts of energy and are complex to operate and maintain. A failure to provide a source of reliable energy and the capacity to implement, maintain and operate these systems is a significant contributor to water scarcity risks in Africa ( [[#Muller--2016|Muller and Wright, 2016]] ). Soft adaptation options include increasing water use efficiency, changing agricultural practices, more appropriate water pricing ( [[#Olmstead--2014|Olmstead, 2014]] ) and enhancing capacity to tackle groundwater overexploitation ( [[#Kuper--2016|Kuper et al., 2016]] ), among others (see [[#9.10.2.4|Section 9.10.2.4]] and [[IPCC:Wg2:Chapter:Chapter-4|Chapter 4]] Sections 4.6 and 4.7).

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==== 9.7.3.6 Mainstreaming Gender Across all Adaptation Options ====

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Gender is important in building resilience and adaptation pathways to global environmental change ( [[#Ravera--2016|Ravera et al., 2016]] ). It is well-established that women, in most societies, have accumulated considerable knowledge about water resources, including location, quality and storage methods because they are primarily responsible for the management of water for household water supply, sanitation and health, and for productive uses in subsistence agriculture ( [[#UN-Water--2006|UN-Water, 2006]] ). As gender-differentiated relationships are complex, adaptation should take into account intersectional differences such as homeownership, employment and age ( [[#Harris--2016|Harris et al., 2016]] ), educational, infrastructural and programmatic interventions ( [[#Pouramin--2020|Pouramin et al., 2020]] ), aspects of protection and safety ( [[#Mackinnon--2019|Mackinnon et al., 2019]] ), barriers to adaptation and gendered differences in the choice of adaptation measures ( [[#Mersha--2016|Mersha and Van Laerhoven, 2016]] ), the complex power dynamics of existing social and political relations ( [[#Djoudi--2016|Djoudi et al., 2016]] ; [[#Rao--2017|Rao et al., 2017]] ), and inclusion and empowerment of women in the management of environmental resources ( [[#Makina--2016|Makina and Moyo, 2016]] ). Incorporation of gender and water inequities into climate change adaptation would have a significant impact on achieving the SDGs (particularly 1, 3, 4, 5 and 6), while failure to incorporate gender will undermine adaptation efforts ( [[#Bunce--2015|Bunce and Ford, 2015]] ; [[#Fleifel--2019|Fleifel et al., 2019]] ; [[#Pouramin--2020|Pouramin et al., 2020]] ).

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'''Box 9.5 | Water–energy–food nexus'''
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The interdependencies in the water-energy-food (WEF) nexus, coupled with its high exposure to climate change, amplify WEF risks. Risks can be transmitted from one WEF sector to the other two with cascading risks to human health, cities and infrastructure ( [[#Conway--2015|Conway et al., 2015]] ; [[#Mpandeli--2018|Mpandeli et al., 2018]] ; [[#Nhamo--2018|Nhamo et al., 2018]] ; [[#Yang--2018|Yang and Wi, 2018]] ; [[#Ding--2019|Ding et al., 2019]] ; [[#Simpson--2021b|Simpson et al., 2021b]] ). For example, increasing demand for water for agricultural and energy production is driving an increasing competition over water resources between food and energy industries which, among other effects, compromises the nutritional needs of local populations ( [[#Zografos--2014|Zografos et al., 2014]] ; [[#Dottori--2018|Dottori et al., 2018]] ). Drought events, such as in southern Africa during the 2015/16 El Niño, have been associated with major multi-sector impacts on food security (over 40 million food-insecure people and extensive livestock deaths) and reduced energy security through disruption to hydropower generation (associated in Zambia with the lowest rate of real economic growth in over 15 years) ( [[#Nhamo--2018|Nhamo et al., 2018]] ). The WEF nexus of the Nile and Zambezi river basins, which include many of Africa’s largest existing hydropower dams, have received the most attention. In these two regions, where socioeconomic development is already driving up demand, projections indicate that water scarcity may be exacerbated by drying ( [[#Munday--2019|Munday and Washington, 2019]] ) and increased flow variability ( [[#Siam--2017|Siam and Eltahir, 2017]] ). However, for Africa more widely, very few studies fully integrate all three WEF nexus sectors and rarely include an explicit focus on climate change.

In Africa, the climate risks that the water, energy and food sectors will face in the future are heavily influenced by the infrastructure decisions that governments make in the near term. The AU’s Programme for Infrastructure Development (PIDA), along with other national energy plans (jointly referred to as PIDA+), aim to increase hydropower capacity nearly six-fold, irrigation capacity by over 60% and hydropower storage capacity by over 80% in major African river basins ( [[#Cervigni--2015|Cervigni et al., 2015]] ). The vast majority of hydropower additions would occur in the Congo, Niger, Nile and Zambezi river basins, and the majority of the irrigation capacity additions would occur in the Niger, Nile and Zambezi River basins (Figure Box 9.5.1; [[#Huber-Lee--2015|Huber-]] [[#Lee--2015|Lee et al., 2015]] ).

Climate change risk to the productivity of this rapidly expanding hydropower and irrigation infrastructure compound the overall WEF nexus risk. Future levels of rainfall, evaporation and runoff will have a substantial impact on hydropower and irrigation production. Climate models disagree on whether climates will become wetter or dryer in each river basin. [[#Cervigni--2015|Cervigni et al. (2015)]] modelled revenues from the sale of hydroelectricity and irrigated crops in major African river basins under different climate scenarios between 2015 and 2050 (Figure Box 9.5.1). The study found that hydropower revenues in the driest climate scenarios could be 58% lower in the Zambezi River basin, 30% lower in the Orange basin and 7% lower in the Congo basin relative to a scenario with current climate conditions. Hydropower revenues in the wettest climate scenario could be more than 20% higher in the Zambezi river basin and 50% higher in the Orange basin. The biggest risk to the production of irrigated crops is in the eastern Nile where irrigation revenue could be 34% lower in the driest scenario and 11% higher in the wettest than in a scenario without climate change ( [[#Cervigni--2015|Cervigni et al., 2015]] ).

Studies have used the river basin as a unit of analysis and adopted sophisticated techniques to assess and present trade-offs between competing uses. For example, [[#Yang--2018|Yang and Wi (2018)]] consider the WEF nexus in the Great Ruaha tributary of the Rufiji River in Tanzania motivated by an observed decrease in streamflow during the dry season in the 1990s, but without an explicit focus on climate. [[#Yang--2018|Yang and Wi (2018)]] show sensitivity of water availability for irrigated crop production to warming, and sensitivity of hydropower generation and ecosystem health to changes in precipitation and dam development. Understanding of WEF nexus interlinkages can help characterise risks and identify entry points and the relevant institutional levels for cross-sectoral climate change adaptation actions ( [[#England--2018|England et al., 2018]] ). An integrated response can be enhanced through the inclusion of community-based organisations, such as water resource user associations and the wide range of other multi-sectoral actors involved in and affected by development decisions. Capturing the scarcity values of water and energy embedded in food and other products can help identify the co-benefits and costs of integrated adaptation ( [[#Allan--2015|Allan et al., 2015]] ).

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'''Figure Box 9.5.1 |''' '''Climate risks to hydropower and irrigation in Africa.'''

'''(a)''' The map shows the location and size of existing (blue) and planned (orange) hydropower plants in African governments’ infrastructure expansion plans, 2015–2050.

'''(b)''' Matrix shows historical correlations in annual river flows between some of the major river basins indicating risk of hydropower shortages where correlations are higher. (c, e) Existing and planned hydropower and irrigation are indicated in charts. Dark blue shows forecasted revenues from 2015–2050 of existing hydropower and irrigation in major African river basins in a scenario without further climate change (i.e., based on historical data). Orange in charts (c, e) shows the expected increase in hydropower and irrigation revenues as new hydropower and irrigation infrastructure is added based on planned infrastructure development (PIDA+) in a scenario without climate change.

'''(d, f)''' The bar graphs show the forecast revenues for hydropower and irrigation infrastructure in each river basin under 121 different climate scenarios from 2015–2050, highlighting risk to revenues from high variability in river discharge due to climate change. In river basins with a wide range of potential river flow outcomes due to climate change, such as the eastern Nile and Zambezi, there is substantial uncertainty around revenue forecasts and potential for large reductions in future revenue. Hydropower revenues refer to net present value of hydroelectricity produced in each river basin over the period 2015–2050, and irrigation revenues refer to the crop revenues per hectare for each crop multiplied by the number of hectares of each crop across the basin. All figures are estimates of the net present value of revenues, using a discount rate of 3%, and are in 2012 USD billions. The 121 potential climate futures were derived using different General Circulation Models (GCMs), Representative Concentration Pathways (RCPs), and downscaling methods. IPCC AR4 and AR5 provided data from 22 and 23 GCMs, respectively. These were evaluated across two or three emissions pathways, including RCP4.5 and RCP8.5. The Bias Corrected Spatial Disaggregation method of downscaling was then used to derive 99 potential climate futures. An additional 22 climate futures (11 GCMs driven by the RCP4.5 and RCP8.5 emissions pathways) were produced using the Empirical Statistical Downscaling Methods developed at the Climate Systems Analysis Group at the University of Cape Town. Data sourced from [[#Cervigni--2015|Cervigni et al. (2015)]] .

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