Editing IPCC:AR6/WGII/Chapter-4 (section)

=== 4.5.3 Projected Risks to Water, Sanitation and Hygiene (WaSH) ===

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Climate-related extreme events impact WaSH services and local water security. While not WaSH-specific, AR5 showed that more people would experience water scarcity and floods ( ''high confidence'' ) and identified WaSH failure due to climate change as an emergent risk ( ''medium confidence'' ) leading to higher diarrhoea risk ( [[#Field--2014b|Field et al., 2014b]] ). In addition, both SR1.5 ( [[#IPCC--2018a|IPCC, 2018a]] ) and SRCCL ( [[#IPCC--2019b|IPCC, 2019b]] ) projected the risk from droughts, heavy precipitation, water scarcity, wildfire damage and permafrost degradation to be higher at 2°C warming than 1.5°C ( ''medium confidence'' ), and all these could potentially impact water quality and WaSH services.

Waterborne diseases result from complex causal relationships between climatic, environmental and socioeconomic factors that are not fully understood or modelled ( [[#Boholm--2017|Boholm and Prutzer, 2017]] ) ( ''high confidence'' ). WaSH-related health risks are related to extreme events, harmful algal blooms and WaSH practices ( [[IPCC:Wg2:Chapter:Chapter-7|Chapter 7]] WGII 7.3.2). In addition, changes in thermotolerance and chlorine resistance of certain viruses have been observed in laboratory experiments simulating different temperatures and sunlight conditions ( [[#Carratalà--2020|Carratalà et al., 2020]] ), increasing potential health risks even where traditional water treatment exists ( [[#Jiménez%20Cisneros--2014|Jiménez Cisneros et al., 2014]] ) ( ''low confidence'' ). Studies show that degraded water quality increases the willingness to pay for clean water regardless of national economic status. However, payment for clean, potable water, particularly in low- and middle-income countries, can represent a significant percentage of people’s income, limiting economic well-being and the possibility for re-investment in other livelihoods or activities ( [[#Constantine--2017|Constantine et al., 2017]] ; [[#van%20Houtven--2017|van Houtven et al., 2017]] ; [[#Price--2019|Price et al., 2019]] ).

Collectively, drinking water treatment, sanitation and hygiene interrupt disease transmission pathways, particularly for water-related diseases. However, WaSH systems themselves are vulnerable to extreme events ( [[#4.3.3|Section 4.3.3]] ). For example, sewage overflows resulting from heavy rainfall events are expected to increase waterborne disease outbreaks ( [[#Khan--2015|Khan et al., 2015]] ). High diarrhoeal disease burdens mean that small changes in climate-associated risk are projected to have significant impacts on disease burdens ( [[#Levy--2018|Levy et al., 2018]] ). For example, up to 2.2 million more cases of ''E. coli'' by 2100 in Bangladesh under a 2.1°C GWL are projected ( [[#Philipsborn--2016|Philipsborn et al., 2016]] ), while up to an 11-fold and 25-fold increase by 2050 and 2080, respectively, under a 2–4°C GWL, in disability-adjusted life years, associated with cryptosporidiosis and giardiasis in Canada is projected ( [[#Smith--2015|Smith et al., 2015]] ). In addition, an additional 48,000 deaths of children under 15 years of age globally from diarrhoea by 2030 are also projected ( [[#WHO--2014|WHO, 2014]] ). Notably, high levels of treatment compliance and boiling water before consumption offset the projected impact of climate change on giardiasis in Canada in the 2050 scenario, but could not wholly offset the projected impact in 2080 ( [[#Smith--2015|Smith et al., 2015]] ). Climate change impacts on WaSH-attributable disease burden are also projected to delay China’s progress towards disease reduction by almost 9% under RCP8.5 ( [[#Hodges--2014|Hodges et al., 2014]] ). Disruptions in the drinking water supply can lead to increased household water storage, potentially increasing vector larvae breeding habitats (see [[IPCC:Wg2:Chapter:Chapter-3#3.6.3|Section 3.6.3]] ). In combination with the projected expansion of vector ranges given climate change ( [[#Liu-Helmersson--2019|Liu-Helmersson et al., 2019]] ), there is the potential for increased risk of vector-borne disease during periods of water shortage or natural disasters ( [[#4.3.3|Section 4.3.3]] ). Moreover, energy requirements for water and wastewater treatment are indirectly responsible for GHG emissions, while the breakdown of excreta contributes directly to emissions (Box 4.5, [[#4.7.6|Section 4.7.6]] ). These contributions need to be better articulated and accounted for as part of the WaSH and climate change dialogue ( [[#Dickin--2020|Dickin et al., 2020]] ).

In summary, climate change is expected to compromise WaSH services, compounding existing vulnerabilities and increasing water-related health risks ( ''medium evidence, high agreement'' ). Therefore, additional research is required on disease-, country-, and population-specific risks due to future climate change impacts ( [[#Baylis--2017|Baylis, 2017]] ; [[#Bhandari--2020|Bhandari et al., 2020]] ; [[#Harper--2020|Harper et al., 2020]] ).

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