Editing IPCC:AR6/WGI/Chapter-8 (section)

=== Future Water Cycle Changes ===

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'''Without large-scale reduction in greenhouse gas emissions, global warming is projected to cause substantial changes in the water cycle at both global and regional scales''' ( ''high confidence'' ''').''' Global annual precipitation over land is projected to increase on average by 2.4 [–0.2 to +4.7] % ( ''likely'' range) in the SSP1-1.9 low-emissions scenario and by 8.3 [0.9 to 12.9] % in the SSP5-8.5 very high-emissions scenario by 2081–2100, relative to 1995–2014. It is ''virtually certain'' that evaporation will increase over the oceans and ''very likely'' that evapotranspiration will increase over land with regional exceptions in drying areas. There is ''low confidence'' in the sign and magnitude of projected changes in global land runoff in all Shared Socio-economic Pathway scenarios. Projected increases in precipitation amount and intensity will be associated with increased runoff in the northern high latitudes ( ''high confidence'' ). There is ''high confidence'' that mountain glaciers will diminish in all regions and that seasonal snow cover duration will generally decrease. Runoff from small glaciers will typically decrease through loss of ice mass, while runoff from large glaciers is ''likely'' to increase with increasing global warming until glacier mass becomes depleted ( ''high confidence'' ). {4.5.1, 8.4.1}

'''Increased evapotranspiration due to growing atmospheric water demand will decrease soil moisture over the Mediterranean, south-western North America, southern Africa, south-western South America, and south-western Australia''' ( ''high confidence'' ''').''' In the Mediterranean, south-western South America, and western North America, future aridification will far exceed the magnitude of change seen in the last millennium ( ''high confidence'' ). Some tropical regions are also projected to experience increased aridity, including the Amazon basin and Central America ( ''high confidence'' ). {8.4.1}

'''Water cycle variability and extremes are projected to increase faster than average changes in most regions of the world and under all emissions scenarios''' ( ''high confidence'' ''')''' . In the tropics and in the extratropics of both hemispheres during summer/warm season, interannual variability of precipitation and runoff over land is projected to increase at a faster rate than changes in seasonal mean precipitation amount ( ''medium confidence'' ). It is ''very likely'' that rainfall variability related to the El Niño–Southern Oscillation will be amplified by the end of the 21st century. Sub-seasonal precipitation variability is also projected to increase, with fewer rainy days but increased daily mean precipitation intensity over many land regions ( ''high confidence'' ). Precipitation extremes will increase in almost all regions ( ''high confidence'' ), even where seasonal mean precipitation is projected to decrease ( ''medium confidence'' ). There is ''high confidence'' that heavy precipitation events associated with both tropical and extratropical cyclones will intensify. {4.5.1.4, 4.5.3.2, 8.2.3.2, 8.4.1, 8.4.2, 8.5.2, 11.7.1.5}

'''There are contrasting projections in monsoon precipitation, with increases in more regions than decreases''' ( ''medium confidence'' ''').''' Summer monsoon precipitation is projected to increase for the South, South East and East Asian monsoon domains, while North American monsoon precipitation is projected to decrease ( ''medium confidence'' ). West African monsoon precipitation is projected to increase over the Central Sahel and decrease over the far western Sahel ( ''medium confidence'' ). There is ''low confidence'' in projected precipitation changes in the South American and Australian monsoons (for both magnitude and sign). There is ''high confidence'' that the monsoon season will be delayed in North and South America and ''medium confidence'' that it will be delayed in the Sahel. {8.2.2, 8.4.2.4}

'''Precipitation associated with extratropical storms and atmospheric rivers will increase in the future in most regions''' ( ''high confidence'' ''').''' A continued poleward shift of storm tracks in the Southern Hemisphere ( ''likely'' ) and the North Pacific ( ''medium confidence'' ) will lead to similar shifts in annual or seasonal precipitation. There is ''low confidence'' in projections of blocking and stationary waves and therefore their influence on precipitation for almost all regions. {8.4.2}

'''The seasonality of precipitation, water availability and streamflow will increase with global warming over the Amazon''' ( ''medium confidence'' ''') and in the subtropics, especially in the Mediterranean and southern Africa''' ( ''high confidence'' ''').''' The annual contrast between the wettest and driest month of the year is ''likely'' to increase by 3–5% per 1°C in most monsoon regions in terms of precipitation, precipitation minus evaporation, and runoff ( ''medium confidence'' ). There is ''high confidence'' in an earlier onset in spring snowmelt, with higher peak flows at the expense of summer flows in snow-dominated regions globally, but ''medium confidence'' that reduced snow volume in lower-latitude regions will reduce runoff from snowmelt. {8.2.2, Box 8.2, 8.4.1.7, 8.4.2.4}

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