Editing IPCC:AR6/WGII/Chapter-15 (section)

==== 15.3.4.3 Water Security ====

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Climate change impacts on freshwater systems frequently exacerbate existing pressure, especially in locations already experiencing water scarcity ( [[#15.3.3.2|Section 15.3.3.2]] and Cross-Chapter Box INTERREG in Chapter 16; [[#Schewe--2014|Schewe et al., 2014]] ; [[#Holding--2016|Holding et al., 2016]] ; [[#Karnauskas--2016|Karnauskas et al., 2016]] ), making water security a key risk (KR4 in Figure 15.5) in small islands. Small islands are usually environments where demand for resources related to socioeconomic factors such as population growth, urbanisation and tourism already place increasing pressure on limited freshwater resources. In many small islands, water demand already exceeds supply. For example, in the Caribbean, Barbados is utilising close to 100% of its available water resources and St. Lucia has a water supply deficit of approximately 35% ( [[#Cashman--2014|Cashman, 2014]] ). On many Mediterranean islands, water demand regularly outstrips supply as a result of low average precipitation coupled with increasing water demand from economic activities such as irrigated agriculture and tourism ( [[#Hof--2014|Hof et al., 2014]] ; [[#Papadimitriou--2019|Papadimitriou et al., 2019]] ).

Population growth plays a major role in projected future water stress ( [[#Schewe--2014|Schewe et al., 2014]] ). Combining projected aridity change (fractional change compared to historical climatology) with population projections derived from SSP2 shows that the SIDS with high projected population growth rates are expected to experience the most severe freshwater stress by 2030 under a 2°C warming threshold scenario ( [[#Karnauskas--2018|Karnauskas et al., 2018]] ). For several SIDS (e.g., Belize and Jamaica), increasing aridity change is a prominent exacerbating factor, but for others (e.g., the Solomon Islands and Comoros) population growth is the main factor. An increase in temperature of 1°C (from 1.7°C to 2.7°C) could result in a 60% increase in the number of people projected to experience severe water resources stress in the period 2043–2071 ( [[#Schewe--2014|Schewe et al., 2014]] ; [[#Karnauskas--2018|Karnauskas et al., 2018]] ). Research on Jamaica concluded that the ability of rainwater harvesting to meet potable water needs between the 2030s and 2050s will be reduced based on predicted shorter intense showers and frequent dry spells ( [[#Aladenola--2016|Aladenola et al., 2016]] ).

The Caribbean and Pacific regions have historically been affected by severe droughts ( [[#Peters--2015|Peters, 2015]] ; [[#FAO--2016|FAO, 2016]] ; [[#Barkey--2017|Barkey and Bailey, 2017]] ; [[#Paeniu--2017|Paeniu et al., 2017]] ; [[#Trotman--2017|Trotman et al., 2017]] ; [[#Anshuka--2018|Anshuka et al., 2018]] ) with significant physical impacts and negative socioeconomic outcomes. Water quality is affected by drought as well as water availability. The El Niño related 2015–1016 drought in Vanuatu led to reliance on small amounts of contaminated water left at the bottom of household tanks ( [[#Iese--2021a|Iese et al., 2021a]] ). The highest land disturbance percentages have coincided with major droughts in Cuba ( [[#de%20Beurs--2019|de Beurs et al., 2019]] ). Drought has been shown to have an impact on rainwater harvesting in the Pacific ( [[#Quigley--2016|Quigley et al., 2016]] ) and Caribbean ( [[#Aladenola--2016|Aladenola et al., 2016]] ), especially in rural areas where connections to centralised public water supply have been difficult. Increasing trends in drought are apparent in the Caribbean ( [[#Herrera--2017|Herrera and Ault, 2017]] ) although trends in the western Pacific are not statistically significant ( [[#McGree--2016|McGree et al., 2016]] ).

Areas where a freshwater lens is thinner are most likely to be impacted by multiple climate stressors, and these areas tend to be in coastal zones where populations are likely to be most concentrated ( [[#Holding--2016|Holding et al., 2016]] ). In Barbados, where groundwater is relied upon for food production, urban use and environmental needs, higher food prices are expected in the future if informed land use management and integrated water resources policies are not implemented to manage groundwater in the short term, even with modest climate change threats ( [[#Gohar--2019|Gohar et al., 2019]] ).

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