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

== 9.7 Water ==

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Much of Africa experiences very high hydrological variability in all components of the water cycle, with important implications for people and ecosystems. Most of the continent’s water is stored in groundwater (660,000 km 3 ), which is 20 times more than the water stored in the lakes and 100 times more than the annual renewable water resources ( [[#MacDonald--2012|MacDonald et al., 2012]] ). The accessible volume of groundwater via wells and springs is smaller than these estimates ( [[#Xu--2019|Xu et al., 2019]] ). Africa has 63 transboundary river basins ( [[#UNEP--2010|UNEP, 2010]] ), 72 mapped transboundary aquifers ( [[#Nijsten--2018|Nijsten et al., 2018]] ) and 33 transboundary lakes ( [[#ILEC%20and%20UNEP--2016|ILEC and UNEP, 2016]] ), reflecting a highly water-connected and interdependent socio-ecological system across countries, also extending to the coastal areas of the continent (see [[IPCC:Wg2:Chapter:Chapter-4|Chapter 4]] [[IPCC:Wg2:Chapter:Chapter-4#4.1|Section 4.1]] ).

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=== 9.7.1 Observed Impacts from Climate Variability and Climate Change ===

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Climate impacts on water are occurring against a backdrop of increasing temperatures and changes in rainfall, with increased seasonal and interannual variability, droughts in some regions, and increased frequency of heavy rainfall events (see [[#9.5|Section 9.5]] ). In west Africa, declines in river flows have been attributed to declining rainfall and increasing temperature, drought frequency and water demand ( [[#Biao--2017|Biao, 2017]] ; [[#Thompson--2017|Thompson et al., 2017]] ; [[#Descroix--2018|Descroix et al., 2018]] ). In central Africa, the Congo river demonstrates inter-decadal shifts but no long-term trend ( [[#Mahe--2013|Mahe et al., 2013]] ; [[#Alsdorf--2016|Alsdorf et al., 2016]] ). However, recently observed falling water levels in its upper and middle reaches are attributed to climate change ( [[#von%20Lossow--2017|von Lossow, 2017]] ).

A review of river flow and lake level changes in 82 basins in eastern and southern Africa regions for 1970–2010 showed mixed trends: 51% had decreasing trends ranging from 10–49% and 11% increasing trends ranging from 7–60% ( [[#Schäfer--2015|Schäfer et al., 2015]] ). However, in southern Africa as a whole, river flows have mostly decreased ( ''high confidence'' ) ( [[#Dallas--2014|Dallas and Rivers-Moore, 2014]] ). In east Africa, large rivers such as the Tana show increasing flow (1941–2016) related to increased rainfall in the highlands, with little influence of flow regulation by a series of dams ( [[#Langat--2017|Langat et al., 2017]] ). The Nile river basin has been experiencing a mainly increasing rainfall trend upstream and decreasing trend downstream ( [[#Onyutha--2016|Onyutha et al., 2016]] ). The observed changes are driven by a complex coupling of changes in climate, land use and water demand.

Observed climate changes in Africa (see [[#9.5|Section 9.5]] ) have led to changes in river flow and runoff ( [[#Dallas--2014|Dallas and Rivers-Moore, 2014]] ; [[#Wolski--2014|Wolski et al., 2014]] ) and high fluctuations in lake levels ( ''high confidence'' ) ( [[#Natugonza--2016|Natugonza et al., 2016]] ; [[#Ogutu-Ohwayo--2016|Ogutu-Ohwayo et al., 2016]] ; [[#Gownaris--2018|Gownaris et al., 2018]] ). Shallow lakes respond dramatically to hydrological changes, for example, Lake Chilwa has dried up completely nine times in the last century ( [[#Wilson--2014|Wilson, 2014]] ), while Lake Chad shrunk by 90% between 1963 and 2000 ( [[#Gao--2011|Gao et al., 2011]] ). However, recent analyses indicate that Lake Chad’s water levels have been stable since 2000 due to infilling from groundwater resources ( [[#Buma--2018|Buma et al., 2018]] ; [[#Pham-Duc--2020|Pham-Duc et al., 2020]] ). Other factors such as deforestation and increased water use in upstream tributaries also contribute to lake shrinking ( [[#Mvula--2014|Mvula et al., 2014]] ). Water levels in Kenya’s mostly shallow rift lakes have been rising since 2010, with some exceeding historical record high levels ( [[#Schagerl--2016|Schagerl and Renaut, 2016]] ; [[#Olago--2021|Olago et al., 2021]] ). The recent 10-year rising trend is partly attributed to increased rainfall and changing land uses ( [[#Onywere--2012|Onywere et al., 2012]] ; [[#Olago--2021|Olago et al., 2021]] ). Changes in water level fluctuations of 13 African lakes have been positively correlated with primary and overall production ( [[#Gownaris--2018|Gownaris et al., 2018]] ), and will have important consequences for freshwater ecosystems and related ecosystem goods and services (see Sections 9.6.1.3; 9.8.5). Other effects of observed climate changes in Africa include higher episodic groundwater recharge, particularly in drylands, from heavy rainfall events that are in some cases related to ENSO and the IOD ( [[#Taylor--2013|Taylor et al., 2013]] ; [[#Fischer--2016|Fischer and Knutti, 2016]] ; [[#Cuthbert--2019|Cuthbert et al., 2019]] ; [[#Kotchoni--2019|Kotchoni et al., 2019]] ; [[#Myhre--2019|Myhre et al., 2019]] ), reduced soil moisture, more frequent and intense floods, more persistent and frequent droughts ( [[#Douville--2021|Douville et al., 2021]] ) and the steady decline and projected disappearance by 2040 of African tropical glaciers (see [[#9.5.9|Section 9.5.9]] ).

The mixed signal in river flow trends (increase/decrease/no change) across Africa mirrors the results seen globally for runoff and streamflow (see [[IPCC:Wg2:Chapter:Chapter-4|Chapter 4]] [[IPCC:Wg2:Chapter:Chapter-4#4.2.3|Section 4.2.3]] ). Hydrological extremes are, however, of increasing concern. There has been an increase in drought frequency, severity and spatial extent in recent decades. From 1900–2013, Africa suffered the largest number of drought events globally and registered the second largest number of people affected after Asia ( [[#Masih--2014|Masih et al., 2014]] ). The likelihood of recent severe climate conditions such as the multi-year Cape Town drought has increased due to human-caused climate change ( [[#Otto--2018|Otto et al., 2018]] ; [[#Pascale--2020|Pascale et al., 2020]] ; see Box 9.4), and regional and urban floods ( [[#Yuan--2018|Yuan et al., 2018]] ; [[#Tiitmamer--2020|Tiitmamer, 2020]] ) and droughts ( [[#Funk--2018b|Funk et al., 2018b]] ; [[#Siderius--2018|Siderius et al., 2018]] ; [[#Uhe--2018|Uhe et al., 2018]] ) are expected to increase.

However, between 2010–2020 more people across Africa have been impacted by floods (e.g., related to Cyclone Idai in March 2019) compared to droughts ( [[#Lumbroso--2020|Lumbroso, 2020]] ). Coastal cities are vulnerable to floods related to rainfall and sea level rise ( [[#Musa--2014|Musa et al., 2014]] ), as exemplified by the flood disasters experienced in the Niger delta in 2012 which displaced more than 3 million people and destroyed schools, clinics, markets and electricity installations ( [[#Amadi--2015|Amadi and Ogonor, 2015]] ). From 2000–2015, the proportion of people exposed to floods grew by 20–24%, mostly in Africa and Asia, with Mozambique and multiple countries in West Africa estimated to have had the proportion of their populations exposed to flooding increase by more than 50% ( [[#Tellman--2021|Tellman et al., 2021]] ) and these numbers will increase under climate change. Sectoral impacts from flooding within Africa and globally are further elaborated on in Sections 9.8.2 and 9.8.5.1, Table 9.3 and [[IPCC:Wg2:Chapter:Chapter-4|Chapter 4]] [[IPCC:Wg2:Chapter:Chapter-4#4.3|Section 4.3]] .

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'''Box 9.4 | African cities facing water scarcity'''
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Many African cities will face increasing water scarcity under climate change ( [[#Grasham--2019|Grasham et al., 2019]] ). The Cape Town and Dodoma cases illustrate challenges for both surface and groundwater supply and what adaptation responses have been employed.

The Cape Town drought (2015–2018)

The Cape Town drought illustrates how a highly diverse African city and its citizens responded to protracted and unanticipated water scarcity. Human-caused climate change made the reduced rainfall that caused the drought three times more ''likely'' (95% confidence interval 1.5–6) ( [[#Otto--2018|Otto et al., 2018]] ; [[#Pascale--2020|Pascale et al., 2020]] ; [[#Doblas-Reyes--2021|Doblas-Reyes et al., 2021]] ). After three consecutive years of low precipitation, Cape Town braced for a ‘Day Zero’ where large portions of the city would lose water supply ( [[#Cole--2021a|Cole et al., 2021a]] ). The risk of Day Zero was anticipated to cascade to affect risks to health, economic output and security ( [[#Simpson--2021b|Simpson et al., 2021b]] ). The case study highlights the importance of communication, budgetary flexibility, robust financial buffers and insurance mechanisms, disaster planning, intergovernmental cooperation, nature-based solutions, infrastructure transformations and equitable access for climate adaptation in African cities facing water scarcity.

A substantial media campaign was launched to inform residents about the severity of the drought and urge water conservation ( [[#Booysen--2019|Booysen et al., 2019]] ; [[#Hellberg--2019|Hellberg, 2019]] ; [[#Ouweneel--2020|Ouweneel et al., 2020]] ). Together with stringent demand management through higher water tariffs, this communication campaign played an important role in reducing consumption from 540 to 280 litres per household per day ( [[#Booysen--2019|Booysen et al., 2019]] ; [[#Simpson--2019a|Simpson et al., 2019a]] ). Revenue from water sales contributes 14% of Cape Town’s total revenue, making it the third-largest source of ‘own’ revenue for the city ( [[#Simpson--2019b|Simpson et al., 2019b]] ). However, with an unprecedented reduction in water use, the municipal budget was undermined ( [[#Simpson--2020b|Simpson et al., 2020b]] ). Collecting less revenue created a financial shock as the city struggled to recover operating finance, even while new capital requirements were needed for the development of expensive new water supply projects ( [[#Simpson--2019b|Simpson et al., 2019b]] ). This financial shock was compounded by the economic stress of poor agricultural and tourism performance brought about by the drought ( [[#Shepherd--2019|Shepherd, 2019]] ; [[#Simpson--2021b|Simpson et al., 2021b]] ). As wealthy residents invested in private, off-grid water supplies, the risk of reduced municipal revenue collections from newly off-grid households aggregated with the risk of reduced tourism, increasing the risk to the reputation of the incumbent administration ( [[#Simpson--2021b|Simpson et al., 2021b]] ). This demonstrates how a population cohort with a high response capability to water scarcity can reduce risk while simultaneously increasing risks to the municipality and its capacity to provide water to vulnerable residents ( [[#Simpson--2020b|Simpson et al., 2020b]] ). Given that city populations in Africa pay 5–7 times more for water than the average price paid in the USA or Europe ( [[#Adamu--2017|Adamu and Ndi, 2017]] ; [[#Lwasa--2018|Lwasa et al., 2018]] ), municipal finance needs to delink operating revenue from potential climate shocks (see Box 8.6).

The drought led the municipality to consider a broader diversity of water supply options, including groundwater ( [[#CoCT--2019|CoCT, 2019]] ), developing city-scale, slow-onset disaster planning ( [[#Cole--2021a|Cole et al., 2021a]] ) and building an enhanced ‘relationship with water’ ( [[#CoCT--2019|CoCT, 2019]] ; [[#Madonsela--2019|Madonsela et al., 2019]] ). This shift in approach is displayed in the recognition of nature-based solutions as a priority in water resilience-building efforts ( [[#Rodina--2019|Rodina, 2019]] ) and is signalled in Cape Town’s Water Strategy which aims to become a ‘water sensitive city’ that makes ‘optimal use of stormwater and urban waterways for flood control, aquifer recharge, water re-use and recreation’ ( [[#CoCT--2019|CoCT, 2019]] ).

The drought required cooperation between multiple spheres of government, and the management of a broad range of stakeholders and political entities ( [[#Nhamo--2019|Nhamo and Agyepong Adelaide, 2019]] ; [[#Cole--2021a|Cole et al., 2021a]] ). The case highlights how a lack of coordination between essential organs of state and political entities can reduce response efficacy ( [[#Rodina--2019|Rodina, 2019]] ). Despite significant investments in water security by public and private entities, one-quarter of Cape Town’s population remains in persistent conditions of water stress, emphasising the challenge and importance of inclusive solutions that address the persistent social and economic stressors which affect vulnerability to water scarcity ( [[#Enqvist--2019|Enqvist and Ziervogel, 2019]] ).

Sustaining intensive groundwater use in a dryland city under climate change: Dodoma, Tanzania

Since 1954, the Makutapora wellfield in semi-arid, central Tanzania has supplied safe water to the city of Dodoma. Substantial rises in wellfield pumping and population growth have increased freshwater demand in Dodoma and dependence upon the Makutapora wellfield, currently the sole perennial source of piped water to the city. Yet, there is high uncertainty of groundwater recharge rates ( [[#Nkotagu--1996|Nkotagu, 1996]] ; [[#Taylor--2013|Taylor et al., 2013]] ) which rely on intense seasonal rainfall associated with the ENSO and the IOD modes of climate variability (e.g., 2 to 7 years) to contribute disproportionately to recharge ( [[#Taylor--2013|Taylor et al., 2013]] ; [[#Kolusu--2019|Kolusu et al., 2019]] ).

Defining a sustainable pumping rate for the Makutapora wellfield is complicated by the variable and episodic nature of groundwater replenishment in this dryland environment. For example, groundwater recharge during the 1997/1998 El Niño event, the strongest El Niño event of the 20th century, accounted for nearly 20% of all of the recharge received from 1955–2010 ( [[#Taylor--2013|Taylor et al., 2013]] ), highlighting the vital role interannual groundwater storage plays in enabling adaptation to climate variability and change in drylands. The disproportionate contribution of intense seasonal rainfalls to the replenishment of the Makutapora wellfield, consistent with observations from across sub-Saharan Africa ( [[#Cuthbert--2019|Cuthbert et al., 2019]] ), suggests that groundwater in drylands are currently naturally resilient to climate change. However, it remains unclear whether climate change will strengthen or weaken the influence of ENSO and IOD on rainfall ( [[#Brown--2020|Brown et al., 2020]] ) and thereby affect the predictability of groundwater recharge.

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Box 9.4

As freshwater demand in Tanzania’s rapidly growing capital is projected to increase substantially in the coming decades, questions remain as to whether the capacity of the Makutapora wellfield can meet some or all of this demand. Nature-based solutions to improve the resilience of wellfield abstraction to increased pumpage and climate change include managed aquifer recharge (MAR). The sharing of general lessons learned from other cities in dryland Africa employing MAR, such as Windhoek in Namibia ( [[#Murray--2018|Murray et al., 2018]] ), could prove invaluable.

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=== 9.7.2 Projected Risks and Vulnerability ===

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==== 9.7.2.1 Projected Risks ====

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By 2050, up to 921 million additional people in sub-Saharan Africa could be exposed to climate change-related water stress, while up to 459 million could experience reduced exposure ( [[#Dickerson--2021|Dickerson et al., 2021]] ). This large variance in numbers and direction of change is related to uncertainties in climate models and non-climate factors like population growth and water withdrawals ( [[#Dickerson--2021|Dickerson et al., 2021]] ). The baseline for most of the projected risks presented here is 1971–2000.

In west Africa, significant spatial variability in river flow is projected in the upper reaches of several rivers, with no clear pattern overall ( [[#Roudier--2014|Roudier et al., 2014]] ) and large uncertainties in estimations of change in runoff ( [[#Roudier--2014|Roudier et al., 2014]] ; [[#Bodian--2018|Bodian et al., 2018]] ). In some higher altitude regions, like the Niger Inland Delta in west Africa, river flows and water levels are expected to increase ( ''medium confidence'' ) ( [[#Aich--2014|Aich et al., 2014]] ; [[#Thompson--2017|Thompson et al., 2017]] ). In the Lower Niger Basin, combined average annual rainfall and erosivity for all the climatic models in all scenarios shows increasing rainfall amounts are projected to result in an increasing average change in rainfall-runoff erosivity of about 14%, 19% and 24% for the 2030s, 2050s and 2070s, with concomitant increase in soil loss of 12%, 19% and 21% ( [[#Amanambu--2019|Amanambu et al., 2019]] ). In the Volta River system, increasing wet season river flows (+36% by 2090s) and Volta lake outflow (+5% by 2090s) are anticipated under RCP8.5 ( ''medium confidence'' ) (Awotwi A et al., 2015; [[#Jin--2018|Jin et al., 2018]] ). In the Volta River basin, compared to 1976–2005, drought events are projected to increase by 1.2 events per decade at around 2°C to 1.6 events per decade at around 2.5°C global warming, and drought area extent is projected to increase by 24% to 34% ( [[#Oguntunde--2017|Oguntunde et al., 2017]] ). In central Africa, runoff in the Congo river system may increase by up to 50% (RCP8.5), especially in the wet season, enhancing flood risks in the entire Congo Basin, particularly in the central and western parts ( [[#CSC--2013|CSC, 2013]] ). Average river flows are expected to increase in most parts of central Africa, with expected increases in total potential hydropower production ( [[#Ludwig--2013|Ludwig et al., 2013]] ), but see Box 9.5.

In north Africa, in the upper White Nile basin, [[#Olaka--2019|Olaka et al. (2019)]] project a 25% and 5–10% (RCP4.5) increase in the intensification of future annual rainfall in the eastern and western parts of the Lake Victoria Basin, respectively, with corresponding variability in future river discharge ranging from 5% to 26%. In the upper Blue Nile basin, models also indicate up to 15% increase in runoffs in wet season and up to −24% decrease in dry season during 2021–2040 (RCP8.5) ( [[#Ayele--2016|Ayele et al., 2016]] ; [[#Siam--2017|Siam and Eltahir, 2017]] ; [[#Meresa--2018|Meresa and Gatachew, 2018]] ). The increase of precipitation in the wet season indicates a higher possibility of flash floods, while decreased runoffs in dry season further intensify existing shortage of irrigation water demand ( [[#Ayele--2016|Ayele et al., 2016]] ; [[#Siam--2017|Siam and Eltahir, 2017]] ; [[#Meresa--2018|Meresa and Gatachew, 2018]] ). The annual flow and revenues from hydropower production and irrigated agriculture of the Blue Nile River at Khartoum are projected to increase under maximum but are expected to decrease under minimum and median projected changes in streamflow for 2041–2070 and 2071–2100, respectively ( [[#Tariku--2021|Tariku et al., 2021]] ). The Middle Draa valley in Morocco is expected to experience more severe droughts and the estimation of the water balance suggests a lack of supply in the future ( [[#Karmaoui--2016|Karmaoui et al., 2016]] ).

In east Africa, [[#Liwenga--2015|Liwenga et al. (2015)]] project warmer and wetter conditions in the Great Ruaha River region and with increasing seasonal variation and extremes towards the end of the century. A similar observation is made for the River Pangani, with mean river flow being about 10% higher in the 2050s relative to the 1980–1999 period, associated with a 16–18% increase in rainfall in its upper catchment ( [[#Kishiwa--2018|Kishiwa et al., 2018]] ). However, at more local scales, the projections cover a range of slight declines to significant increases in mean annual rainfall amounts ( [[#Gulacha--2017|Gulacha and Mulungu, 2017]] ). In the Tana River basin in Kenya, water yield is projected to increase progressively under RCP4.5 and RCP8.5 relative to the baseline period 1983–2011 but is characterised by distinct spatial heterogeneity ( [[#Muthuwatta--2018|Muthuwatta et al., 2018]] ).

In southern Africa, reductions in rainfall over the Limpopo and Zambezi river basins under 1.5°C and 2°C global warming could have adverse impacts on hydropower generation, irrigation, tourism, agriculture and ecosystems (Figure Box 9.5.1) ( [[#Maúre--2018|Maúre et al., 2018]] ), although model projections of strong early summer drying trends remain uncertain ( [[#Munday--2019|Munday and Washington, 2019]] ).

Changes in the amplitude, timing and frequency of extreme events such as droughts and floods will continue to affect lake levels, rates of river discharge and runoff and groundwater recharge ( ''high confidence'' ) ( [[#Gownaris--2016|Gownaris et al., 2016]] ; [[#Darko--2019|Darko et al., 2019]] ), but with disparate effects at regional, basin and sub-basin scales, and at seasonal, annual and longer timescales. The increased frequency of extreme rainfall events under climate change ( [[#Myhre--2019|Myhre et al., 2019]] ) is projected to amplify groundwater recharge in drylands ( [[#Jasechko--2015|Jasechko and Taylor, 2015]] ; [[#Cuthbert--2019|Cuthbert et al., 2019]] ). However, declining trends in rainfall and snowfall in some areas of north Africa ( [[#Donat--2014b|Donat et al., 2014b]] ) are projected to continue in a warming world ( [[#Seif-Ennasr--2016|Seif-Ennasr et al., 2016]] ), restricting groundwater recharge from meltwater flows, exacerbating the salinisation and depletion of groundwater ( [[#Hamed--2018|Hamed et al., 2018]] ) and increasing the risk of reduced soil moisture ( [[#Petrova--2018|Petrova et al., 2018]] ) in this region where groundwater abstraction is greatest ( [[#Wada--2014|Wada et al., 2014]] ).

Lake surface temperatures across Africa are expected to rise in tandem with increasing global warming. Lake heatwaves, periods of extreme warm lake surface water temperature, are projected to become hotter and longer (Figure 9.21), with heatwaves more than 300 days per year in many lakes for global warming of 4.2°C ( [[#Woolway--2021|Woolway et al., 2021]] ). Lake warming is expected to have adverse consequences for aquatic biodiversity, habitats, water quality and disruption of current lake physical processes and circulation patterns ( [[#Kraemer--2021|Kraemer et al., 2021]] ).

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[[File:dd51904b20954d199ccfce4042dca12c IPCC_AR6_WGII_Figure_9_021.png]]

'''Figure 9.21 |''' '''Climate change is projected to increase the intensity of lake heatwaves across Africa.''' Projected increases in average intensity of lake heatwaves (°C) under

'''(a)''' 1.8°C global warming (RCP2.6 in 2070–2099) and

'''(b)''' 4.2°C global warming (RCP8.5 in 2070–2099). Each lake is represented by a point. Data were extracted from [[#Woolway--2021|Woolway et al. (2021)]] .

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==== 9.7.2.2 Vulnerability ====

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Climate change is projected to reduce water availability and increase the extent of water scarcity ( [[#Mekonnen--2016|Mekonnen and Hoekstra, 2016]] ), particularly in southern and north Africa, while other regions will be more affected by increased hydrological variability over temporally short to interannual time scales (see [[#9.6.2|Section 9.6.2]] ). African countries are considered to be particularly at risk due to their underlying vulnerabilities ( [[#IPCC--2014b|IPCC, 2014b]] ; [[#UNESCO%20and%20UN-Water--2020|UNESCO and UN-Water, 2020]] ), yet the continents’ water resources are still inadequately quantified and modelled ( [[#Müller%20Schmied--2016|Müller Schmied et al., 2016]] ; [[#Reinecke--2019|Reinecke et al., 2019]] ), constraining sustainable management practices ( [[#Cuthbert--2019|Cuthbert et al., 2019]] ; [[#Hughes--2019|Hughes, 2019]] ).

Hydrological fluctuations are associated with drought, flood and cyclone events which have had multi-sector impacts across Africa ( [[#Siderius--2021|Siderius et al., 2021]] ; see [[IPCC:Wg2:Chapter:Chapter-4|Chapter 4]] Sections 4.3; 4.5), including: reduced crop production ( [[#D’Odorico--2018|D’Odorico et al., 2018]] ), migration and displacement ( [[#Siam--2017|Siam and Eltahir, 2017]] ; [[#IDMC--2018|IDMC, 2018]] ), food insecurity and extensive livestock deaths ( [[#Nhamo--2018|Nhamo et al., 2018]] ), electricity outages ( [[#Gannon--2018|Gannon et al., 2018]] ), increased incidence of cholera ( [[#Olago--2007|Olago et al., 2007]] ; [[#Sorensen--2015|Sorensen et al., 2015]] ; [[#Houéménou--2020|Houéménou et al., 2020]] ) and increased groundwater abstraction amplifying the risk of saline intrusion from sea level rise ( [[#Hamed--2018|Hamed et al., 2018]] ; [[#Ouhamdouch--2019|Ouhamdouch et al., 2019]] ).

The literature shows significant gender-differentiated vulnerability and intersectional vulnerability to climate change impacts on water in Africa ( [[#Fleifel--2019|Fleifel et al., 2019]] ; [[#Grasham--2019|Grasham et al., 2019]] ; [[#Mackinnon--2019|Mackinnon et al., 2019]] ; [[#Dickin--2020|Dickin et al., 2020]] ; [[#Lund%20Schlamovitz--2020|Lund Schlamovitz and Becker, 2020]] ), although studies are generally lacking in northern Africa ( [[#Daoud--2021|Daoud, 2021]] ). Women and girls are, in most cases, more impacted than men and boys by customary water practices, as adult females are the primary water collectors (46% in Liberia to 90% in Cote d’Ivoire), while more female than male children are associated with water collection (62% compared with 38%, respectively) ( [[#Graham--2016|Graham et al., 2016]] ). Women and girls face barriers toward accessing basic sanitation and hygiene resources, and 71% of studies reported a negative health outcome, reflecting a water–gender–health nexus ( [[#Pouramin--2020|Pouramin et al., 2020]] ). These differential vulnerabilities are crucial for informing adaptation, but are still relatively under-researched, more so for the urban poor than rural communities ( [[#Grasham--2019|Grasham et al., 2019]] ; [[#Mackinnon--2019|Mackinnon et al., 2019]] ; [[#Lund%20Schlamovitz--2020|Lund Schlamovitz and Becker, 2020]] ).

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=== 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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<span id="decision-support-tools-for-managing-complex-water-systems"></span>
==== 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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<span id="other-adaptation-options"></span>
==== 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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<span id="mainstreaming-gender-across-all-adaptation-options"></span>
==== 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]] ).

[[File:119b13fe22e5912c99291427dc90a008 IPCC_AR6_WGII_Figure_9_Box_9_5_1.png]]

'''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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