Editing IPCC:AR6/WGI/Chapter-12 (section)

==== 12.3.4.1 Snow, Glacier and Ice Sheet ====

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A large number of indices have been used in water resource and ecosystem studies to track changes in snow under current and future climate conditions, including measurements of the snow water equivalent at key seasonal dates, the fraction of precipitation falling as snow, the first and last days of snow cover, and cold season temperatures ( [[#Mills--2013|Mills et al., 2013]] ; [[#Pierce--2013|Pierce and Cayan, 2013]] ; [[#Berghuijs--2014|Berghuijs et al., 2014]] ; [[#Klos--2014|Klos et al., 2014]] ; [[#Musselman--2017|Musselman et al., 2017]] ; [[#Rhoades--2018|Rhoades et al., 2018]] ). Impact studies also examine shifts in seasonal streamflow for snow-fed river basins ( [[#Mote--2005|Mote et al., 2005]] ; [[#Pederson--2011|Pederson et al., 2011]] ; [[#Beniston--2014|Beniston and Stoffel, 2014]] ; [[#Coppola--2014b|Coppola et al., 2014b]] , 2018; [[#Fyfe--2017|Fyfe et al., 2017]] ; [[#Islam--2017|Islam et al., 2017]] ; [[#Knouft--2017|Knouft and Ficklin, 2017]] ) as well as the geographic extent of snow cover and the depth of frosts when snow cover’s natural insulation is absent ( [[#Scheurer--2009|Scheurer et al., 2009]] ; [[#Millar--2015|Millar and Stephenson, 2015]] ). Studies examining the impact of snow changes on winter recreation and transportation have used thresholds of about 30 cm snow depth or snow water equivalent &gt;10 cm to determine the length of the season for alpine and cross-country skiing and snowmobiling ( [[#Damm--2017|Damm et al., 2017]] ; [[#Wobus--2017b|Wobus et al., 2017b]] ; [[#Spandre--2019|Spandre et al., 2019]] ; [[#Steiger--2019|Steiger et al., 2019]] ; [[#Abegg--2021|Abegg et al., 2021]] ). Changes in snow quality also affect recreational activities ( [[#Rutty--2017|Rutty et al., 2017]] ), and artificial snowmaking can augment recreational snowpack depending on the number of suitable snowmaking hours (e.g., where wet bulb globe temperature (WBGT) &lt;–2.2°C; [[#Wobus--2017b|Wobus et al., 2017b]] ). Local detail may also be provided by tracking the seasonal rain–snow transition line across space and elevation ( [[#Berghuijs--2014|Berghuijs et al., 2014]] ) ( [[#Pierce--2013|Pierce and Cayan, 2013]] ; [[#Berghuijs--2014|Berghuijs et al., 2014]] ; [[#Klos--2014|Klos et al., 2014]] ; [[#Musselman--2017|Musselman et al., 2017]] ).

Change in ice sheet and glacier spatial extent and surface mass balance is relevant for polar and high mountain ecosystems and downstream assets that rely on glacial water resources (J.R. [[#Lee--2017|]] [[#Lee--2017|Lee et al., 2017]] ; [[#Milner--2017|Milner et al., 2017]] ; [[#Huss--2018|Huss and Hock, 2018]] ; [[#Schaefli--2019|Schaefli et al., 2019]] ). The loss of glaciers reduces the thermal consistency of cold streams suitable for some freshwater species ( [[#Giersch--2017|Giersch et al., 2017]] ), and parks and recreation areas may lose appeal as glaciers and seasonal snow cover retreat ( [[#Gonzalez--2018|Gonzalez et al., 2018]] ; [[#Wang--2019|Wang and Zhou, 2019]] ). Rapid glacial retreat can lead to glacial lakes and outburst floods that endanger downstream communities ( [[#Carrivick--2016|Carrivick and Tweed, 2016]] ; [[#Cook--2016|Cook et al., 2016]] ; [[#Harrison--2018|Harrison et al., 2018]] ).

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