Snowpack provides water to more than 50% of the water supply in the arid West, a 2017 study found. “California is the poster child - it does not rain in the summer in California, and so the snowmelt runoff, the snow that waits and runs off later in the season, is absolutely essential for all of the ecosystems, all of the agriculture, all of the cities or anyone who wants water during the dry season,” Lundquist told CNN. The threat to water supplies from declining snow is most pronounced in climates subject to more extreme boom-and-bust cycles of precipitation, like the Mediterranean climate found in California and other parts of the American West, Lundquist said. It is crucial for water supplies because it acts like a natural reservoir, storing water as snow during wet times and then releasing it in the form of snowmelt when water is harder to come by, University of Washington environmental engineering professor Jessica Lundquist told CNN. Less snow falling from the sky also means less snow piling up into snowpack - a deep, persistent cover of snow that accumulates during the winter. Without it, more sunlight is absorbed by the ground, warming the atmosphere. The white of snow acts like a car’s sun shade, deflecting sunlight and its heat back to space. The sun is more direct there compared to the higher latitudes, especially during spring and fall when it still snows. The downward trend is particularly notable in the Northern Hemisphere’s mid-latitudes - the middle area north of the tropics and south of the Arctic, where the US and much of the world’s population resides. There has already been a 2.7% decline in annual global snowfall since 1973, according to Brettschneider’s analysis of data from the European Union’s Copernicus Climate Change Service.
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