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

=== 4.4.7 Projected Changes in Water Quality ===

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AR5 concluded that climate change was projected to reduce water quality ( [[#Jiménez%20Cisneros--2014|Jiménez Cisneros et al., 2014]] ). SR1.5 assessed with ''low confidence'' differences in projected impacts under 1.5°C compared with 2°C of warming ( [[#Hoegh-Guldberg--2018|Hoegh-Guldberg et al., 2018]] ). In addition, SROCC reported water quality degradation due to the release of legacy contaminants in glaciers and permafrost ( ''medium confidence'' ) ( [[#Hock--2019b|Hock et al., 2019b]] ). The AR6 WGI Report does not explicitly mention water quality issues.

Water insecurity due to water quality degradation is projected to increase under climate change due to warming, enhanced floods and sea level rise ( [[#Arnell--2014|Arnell and Lloyd-Hughes, 2014]] ; [[#Dyer--2014|Dyer et al., 2014]] ; [[#Whitehead--2015|Whitehead et al., 2015]] ) ( ''medium confidence'' ). Drought-driven diminishing river and lake levels ( [[#Jeppesen--2015|Jeppesen et al., 2015]] ) and continued water abstraction for irrigation ( [[#Aragüés--2015|Aragüés et al., 2015]] ) may contribute to the salinisation of soil and water. In addition, warming is projected to disrupt the historical sequestration of contaminants in permafrost in the Arctic and mountain regions ( [[#Bond--2018|Bond and Carr, 2018]] ).

Quantitative projections on climate-induced water quality degradation are sparse. Aminomethylphosphonic acid and glyphosate are projected to exceed drinking water quality standards in dry years in a high-emissions scenario in the Meuse River in Europe by 2050 ( [[#Sjerps--2017|Sjerps et al., 2017]] ). From 2020 to 2050, based on scenarios RCP2.6, RCP4.5 and RCP8.5, the incidences of total nitrogen pollution are projected as 97.3, 97.1 and 94.6%, respectively, in drought–flood abrupt alternation months compared to 69.3, 69.7 and 67.5% in normal months in the Luanhe River basin in China ( [[#Bi--2019|Bi et al., 2019]] ). From 2012 to 2050, freshwater river area is expected to decrease from 40.8% to 17.1–19.7% under different sea level rise scenarios in the southwest coastal zone of Bangladesh ( [[#Dasgupta--2013|Dasgupta et al., 2013]] ). Under the warming scenario of +4.8°C increase by the end of the century, the average nutrient abundance is projected to triple in a shallow lake in the northwest of England ( [[#Richardson--2019|Richardson et al., 2019]] ).

While there is some understanding of the potential effect of glacier and permafrost degradation on water quality, projections are lacking. Research is limited mainly in Europe and North America, and quantifying the future water quality changes is still incipient.

In summary, climate change is projected to increase water pollution incidences, salinisation and eutrophication due to increasing drought and flood events, sea level rise and water temperature rise, respectively, in some local rivers and lakes, but there is a dearth of exact quantification at a global scale ( ''medium confidence'' ).

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