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Abstract:
Changing snow cover dynamics is one of the most apparent effects of climate change because of the phase change of snow to liquid water above zero degrees. Impacts of rising temperatures include less snow accumulation, a shorter snow cover season, and an earlier start of the snowmelt season, but little is known about the effects of warming on snowmelt rates. Faster snowmelt should intuitively be the response to a warmer climate. However, a few studies have shown slower snowmelt for snowpacks that melt earlier in the season when less energy (radiation) is available for melt, while others found varying responses across a limited number of sites. Northern Hemisphere scale studies showed a high spatial variability in melt rate change. Here we try to disentangle the complex and mixed effects of rising temperatures on snowmelt dynamics across climates. We use a new pan-Northern Hemisphere SWE dataset (NH-SWE dataset) based on historical snow depth observations and investigate trends in snowmelt rate change from 1981 to 2022. Snowmelt rate remains unchanged if a decrease in snowmelt days is proportional to a reduction in total snowmelt. The interplay between less total snowmelt, earlier snowmelt and its associated radiation change, and a change in temperature during the snow season determine whether snowmelt rates becomes faster or slower. This interplay largely depends on the temperature climate, especially the amplitude of yearly temperatures and the number of days with temperatures nearing zero degrees during the snow season.
