Editing IPCC:AR6/SRCCL/Chapter-7 (section)

==== 7.2.2.4 Dryland water scarcity ====

<div id="section-7-2-2-4-dryland-water-scarcity-block-1"></div>

Water scarcity in drylands contributes to changes in desertification and hazards such as dust storms, increasing risks of economic loss, declines in livelihoods of communities and negative health effects ( ''high confidence'' ) (Section 3.1.3). Further information specific to costs and impacts of water scarcity and droughts is detailed in Cross- Chapter Box 5 in Chapter 3.

The IPCC AR5 report and the SR15 concluded that there is ''low confidence'' in the direction of drought trends since 1950 at the global scale. While these reports did not assess water scarcity with a specific focus on drylands, they indicated that there is ''high confidence'' in observed drought increases in some regions of the world, including in the Mediterranean and West Africa (IPCC AR5) and that there is ''medium confidence'' that anthropogenic climate change has contributed to increased drying in the Mediterranean region (including southern Europe, northern Africa and the western Asia and the Middle east) and that this tendency will continue to increase under higher levels of global warming (IPCC 2018d). Some parts of the drylands have experienced decreasing precipitation over recent decades (IPCC AR5) (Chapter 3 and Section 3.2), consistent with the fact that climate change is implicated in desertification trends in some regions (Section 3.2.2). Dust storms, linked to changes in precipitation and vegetation, appear to be occurring with greater frequency in some deserts and their margins (Goudie 2014 <sup>[[#fn:r110|110]]</sup> ) (Section 3.3.1). There is therefore ''high confidence'' that the transition from undetectable to moderate risk associated with water scarcity in drylands occurred in recent decades in the range 0.7°C to 1°C (Figure 7.1).

Between 1.5°C and 2.5°C, the risk level is expected to increase from moderate to high ( ''medium confidence'' ). Globally, at 2°C an additional 8% of the world population (of population in 2000) will be exposed to new forms of or aggravated water scarcity (IPCC 2018d). However, at 2°C, the annual warming over drylands will reach 3.2°C–4.0°C, implying about 44% more warming over drylands than humid lands (Huang et al. 2017 <sup>[[#fn:r111|111]]</sup> ), thus potentially aggravating water scarcity issues through increased evaporative demand. Byers et al. (2018a) <sup>[[#fn:r112|112]]</sup> estimate that 3–22% of the drylands population (range depending on socio-economic conditions) will be exposed and vulnerable to water stress. The Mediterranean, North Africa and the Eastern Mediterranean will be particularly vulnerable to water shortages, and expansion of desert terrain and vegetation is predicted to occur in the Mediterranean biome, an unparalleled change in the last 10,000 years ( ''medium confidence'' ) (IPCC 2018d <sup>[[#fn:r113|113]]</sup> ). At 2.5°C–3.5°C risks are expected to become very high with migration from some drylands resulting as the only adaptation option ( ''medium confidence'' ). Scarcity of water for irrigation is expected to increase, in particular in Mediterranean regions, with limited possibilities for adaptation (Haddeland et al. 2014 <sup>[[#fn:r1571|1571]]</sup> ).

<div id="section-7-2-2-5-vegetation-degradation"></div>

<span id="vegetation-degradation"></span>