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

=== 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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