Editing IPCC:AR6/SROCC/Chapter-3 (section)

==== 3.4.2.3 Freshwater Systems ====

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Climate model simulations project a warmer and wetter Arctic (Krasting et al., 2013 <sup>[[#fn:r1553|1553]]</sup> ), with increased specific humidity due to enhanced evaporation (Laîné et al., 2014 <sup>[[#fn:r1554|1554]]</sup> ), and moisture flux convergence increases into the Arctic (Skific and Francis, 2013 <sup>[[#fn:r1555|1555]]</sup> ). Increased cold-season precipitation is projected across the Arctic by CMIP5 models (Lique et al., 2016 <sup>[[#fn:r1556|1556]]</sup> ) due to increased moisture flux convergence from outside the Arctic (Zhang et al., 2012 <sup>[[#fn:r1557|1557]]</sup> ) and enhanced moisture availability from reduced sea ice cover (Bintanja and Selten, 2014 <sup>[[#fn:r1558|1558]]</sup> ) ( ''high confidence'' ). Increases in precipitation extremes are also projected over northern watersheds (Kharin et al., 2013 <sup>[[#fn:r1559|1559]]</sup> ; Sillmann et al., 2013 <sup>[[#fn:r1560|1560]]</sup> ), while rain on snow events are expected to increase (Hansen et al., 2014 <sup>[[#fn:r1561|1561]]</sup> ). A net increased ratio of precipitation minus evaporation is projected, resulting in increased freshwater flux from the land surface to the Arctic Ocean, projected to be 30% above current values by 2100 under RCP4.5 (Haine et al., 2015 <sup>[[#fn:r1562|1562]]</sup> ) (Figure 3.10). This is consistent with CMIP5 model projections of increased discharge from Arctic watersheds (van Vliet et al., 2013 <sup>[[#fn:r1563|1563]]</sup> ; Gelfan et al., 2016 <sup>[[#fn:r1564|1564]]</sup> ; MacDonald et al., 2018 <sup>[[#fn:r1565|1565]]</sup> ). The water temperature of this increased discharge is projected to be approximately 1°C warmer than current conditions, increasing the heat flux to Arctic Ocean (van Vliet et al., 2013 <sup>[[#fn:r1566|1566]]</sup> ).

Lake ice phenology is sensitive to projected changes in surface temperature (Sharma et al., 2019 <sup>[[#fn:r1567|1567]]</sup> ). Lake ice models project an earlier spring break-up of between 10–25 days by mid-century (compared with 1961–1990), and up to a 15-day delay in the freeze-up for lakes in the North American Arctic, with more extreme reductions for coastal regions (Brown and Duguay, 2011 <sup>[[#fn:r1568|1568]]</sup> ; Dibike et al., 2011 <sup>[[#fn:r1569|1569]]</sup> ; Prowse et al., 2011 <sup>[[#fn:r1570|1570]]</sup> ) ( ''medium confidence'' ). Mean maximum ice thickness is projected to decrease by 10–50 cm over the same period (Brown and Duguay, 2011 <sup>[[#fn:r1571|1571]]</sup> ). High-latitude warming is projected to drive earlier river ice break-up in spring due to both decreasing ice strength, and earlier onset of peak discharge (Cooley and Pavelsky, 2016 <sup>[[#fn:r1572|1572]]</sup> ). Complex interplay between hydrology and hydraulics in controlling spring flooding and ice jam events complicate projections of these events (Prowse et al., 2010 <sup>[[#fn:r1573|1573]]</sup> ; Prowse et al., 2011 <sup>[[#fn:r1574|1574]]</sup> ).

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