Editing IPCC:AR6/WGII/Chapter-13 (section)

===== 13.2.1.2.2 Low Flows and Water Scarcity =====

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The frequency and severity of low flows are projected to increase, making streamflow drought and water scarcity more severe and persistent in SEU and WCE ( ''medium confidence'' ) (Figure 13.3; [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ), but decreases are projected in most of NEU except the southern UK ( [[#Forzieri--2014|Forzieri et al., 2014]] ; [[#Prudhomme--2014|Prudhomme et al., 2014]] ; [[#Schewe--2014|Schewe et al., 2014]] ; [[#Roudier--2016|Roudier et al., 2016]] ; [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ). In EEU, uncertainty about changes in water scarcity pose distinct challenges for adaptation ( [[#Greve--2018|Greve et al., 2018]] ). At 1.5°C GWL, the number of days with water scarcity (water availability as opposed to water demand) and drought will increase slightly in SEU ( [[#Schleussner--2016|Schleussner et al., 2016]] ; [[#Naumann--2018|Naumann et al., 2018]] ), resulting in 18% of the population exposed to at least moderate water scarcity, increasing to 54% at 2°C GWL ( [[#Byers--2018|Byers et al., 2018]] ). Moderate water scarcity is emerging in some parts of WCE ( [[#Bisselink--2018|Bisselink et al., 2018]] ) increasing to16% of the population under 2°C GWL and SSP2 ( [[#Byers--2018|Byers et al., 2018]] ). Under 4°C GWL, areas in WCE experience water scarcity, especially in summer and autumn. Future intensive water use can aggravate the situation, in particular in SEU (Sections 13.5.1, 13.10.3).

Groundwater abstraction rates reach up to 100 million m³ yr –1 across WCE and SEU, and exceed 100 million m³ yr –1 in parts of SEU ( [[#Wada--2016|Wada, 2016]] ). Low recharge rates lead to a depletion of groundwater resources in parts of SEU and WCE ( [[#Doll--2014|Doll et al., 2014]] ; [[#Wada--2016|Wada, 2016]] ; [[#de%20Graaf--2017|de Graaf et al., 2017]] ), increasing the impacts on water scarcity in SEU. Groundwater pumping and declines in groundwater discharge already threaten environmental flow limits in many European catchments, especially in SEU, extending to almost all basins and sub-basins within the next 30–50 years ( [[#de%20Graaf--2019|de Graaf et al., 2019]] ).

The combined effect of increasing water demand and successive dry climatic conditions further exacerbates groundwater depletion and lowers groundwater levels in SEU but also WCE ( [[#Goderniaux--2015|Goderniaux et al., 2015]] ). Declines in groundwater recharge of up to 30% further increase groundwater depletion ( [[#Aeschbach-Hertig--2012|Aeschbach-Hertig and Gleeson, 2012]] ) especially in SEU and semiarid to arid regions ( [[#Moutahir--2017|Moutahir et al., 2017]] ). Even in WCE and NEU, projected increases in groundwater abstraction will impact groundwater discharge, threatening sustaining environmental flows under dry conditions ( [[#de%20Graaf--2019|de Graaf et al., 2019]] ).

The risks for soil moisture drought are projected to increase in WCE and SEU for all climate scenarios ( [[#Grillakis--2019|Grillakis, 2019]] ; [[#Tramblay--2020|Tramblay et al., 2020]] ; [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ). At 3°C GWL compared with 1.5°C GWL, the drought area will increase by 40% and the population under drought by up to 42%, especially affecting SEU, and to a lesser extent in WCE ( [[#Samaniego--2018|Samaniego et al., 2018]] ).

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