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

==== 13.10.2.3 KR3: Risk of Water Scarcity to Multiple Interconnected Sectors ====

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Risks related to water scarcity across multiple sectors can become severe in WCE and, to a much larger extent, in SEU based on projections of drought damage, population and sectors exposed, and they increase in water exploitation (Figure 13.31a; Table SM13.29). In EEU, uncertainty in hydrological drought projections and risk consequences is higher ( [[#Greve--2018|Greve et al., 2018]] ; [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ; [[#Seneviratne--2021|Seneviratne et al., 2021]] ) and the available number of publications is lower, not allowing a conclusion on how risk levels change with GWL. Yet, there is emerging evidence that drought-related risks increase with warming beyond 3°C GWL also in EEU (Seneviratne, 2021, for hydrological drought and 4°C GWL; Kattsov and Porfiriev, 2020). Evidence from the detected changes and attribution assessment suggests that the risk is already moderate in SEU (e.g., 48 million people exposed to moderate water scarcity between 1981 and 2010) ( ''high confidence'' ) ( [[#13.10.1|Section 13.10.1]] ; Figure 13.31a).

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[[File:a9e6cd50050d2ae16cae6474a0e6f027 IPCC_AR6_WGII_Figure_13_031.png]]

'''Figure 13.31 |''' '''Burning embers and illustrative adaptation pathways for risk of water scarcity to people (Key Risk 3)'''

'''(a)''' Burning ember diagrams for the risk of water scarcity with no or low adaptation, and with high adaptation for SEU and WCE, are shown.

'''(b)''' Illustrative adaptation pathways and key messages (see Figure 13.6). Grey shading means long lead time and dotted lines signal reduced effectiveness. The circles imply transfer to another measure and the bars imply that the measure has reached a tipping point (Table SM13.29).

Risk of water scarcity has a high potential to lead to cascading impacts well beyond the water sector. These materialize in a number of highly interconnected sectors from agriculture and livestock farming to energy (hydropower and cooling of thermal power plants) and industry (e.g., shipping) ( [[#Blauhut--2015|Blauhut et al., 2015]] ; [[#Stahl--2016|Stahl et al., 2016]] ; [[#Bisselink--2020|Bisselink et al., 2020]] ; [[#Cammalleri--2020|Cammalleri et al., 2020]] ). Extensive water extraction will augment pressures on water reserves, impacting the ecological status of rivers and ecosystems dependent on them ( [[#Grizzetti--2017|Grizzetti et al., 2017]] ). Socioeconomic conditions contributing to severe consequences are when more residents settle in drought-prone regions, or when the share of agriculture in GDP declines ( ''high confidence'' ). For Europe, risks of water scarcity will be higher under SSP5 and SSP3 than under SSP1 ( ''medium confidence'' ) ( [[#Byers--2018|Byers et al., 2018]] ; [[#Arnell--2019|Arnell et al., 2019]] ; [[#Harrison--2019|Harrison et al., 2019]] ). Transition to high risks is projected to occur below 2°C GWL in SEU and be associated with more persistent droughts ( [[#13.1.3|Section 13.1.3]] ), and at 2°C GWL to show a 54% increase of the population facing at least moderate levels of water shortage ( [[#Byers--2018|Byers et al., 2018]] ). This transition will happen at higher warming in WCE since risks are projected to increase less rapidly (transition between 2°C and 3°C GWL) ( ''medium confidence'' ) ( [[#13.2.1.2|Section 13.2.1.2]] ; [[#Byers--2018|Byers et al., 2018]] ). At 3°C GWL and beyond, water scarcity will become much more widespread and severe in already water-scarce areas in SEU ( ''high confidence'' ) and will expand to currently non-water-scarce regions in WCE ( ''medium confidence'' ) ( [[#13.2.1.2|Section 13.2.1.2]] ; [[#Bisselink--2018|Bisselink et al., 2018]] ; [[#Naumann--2018|Naumann et al., 2018]] ; [[#Harrison--2019|Harrison et al., 2019]] ; [[#Koutroulis--2019|Koutroulis et al., 2019]] ; [[#Cammalleri--2020|Cammalleri et al., 2020]] ; [[#Spinoni--2020|Spinoni et al., 2020]] ). Decrease in hydropower potential in SEU and WCE are expected beyond 3°GWL (Figure 13.16).

To reduce risk to water scarcity, adaptation measures, at both the supply and the demand side, have been suggested ( [[#13.2.2|Section 13.2.2]] ; Figures 13.6, 13.31b; [[#Garnier--2019|Garnier and Holman, 2019]] ; [[#Hagenlocher--2019|Hagenlocher et al., 2019]] ). Several measures are already in place showing high technical and institutional feasibility (Sections 13.2.2.2, 13.5.2.1). The effectiveness of options varies regionally (in particular between northern and southern regions). For example, in SEU many water reservoirs are already in place. Irrigation is used to support agriculture where rain-fed supplies are not sufficient ( [[#13.5.2|Section 13.5.2]] ). Their future extension depends on available precipitation. Also, wastewater reuse can only be effective if sufficient wastewater is available. Improvements in water efficiency and behavioural changes are very effective in SEU (&gt;25% of damages avoided) ( [[#13.2.2.2|Section 13.2.2.2]] ). Investments in large water infrastructures and advanced technologies (including storage), water transfer, water recycling and reuse, and desalination will allow to buy time and therefore to cope with additional warming ( [[#Papadaskalopoulou--2016|Papadaskalopoulou et al., 2016]] ; [[#Greve--2018|Greve et al., 2018]] ). Beyond 2.5°C GWL, transformational adaptation is needed to lower risk levels, such as planned relocation of industry, abandonment of farmland or the development of alternative livelihoods ( [[#Holman--2017|Holman et al., 2017]] ). In WCE, the solution space to water scarcity is expanding with considerable potential for investments in large water infrastructure and advanced technologies (including storage), for reducing risks above 3°C GWL ( [[#Greve--2018|Greve et al., 2018]] ). Under medium warming a larger portfolio of measures might be needed in SEU in particular, although it may not be able to completely avoid water shortages at high warming.

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