FIGURE 4.18 Linear trends in 1 Apr SWE relative to the starting value for the linear fit (i.e., the 1950 value for the best-fit line): (a) at 824 snow course locations in the western United States and Canada for the period 1950-1957, with negative trends shown by red circles and positive by blue circles; (b) from the simulation by the VIC hydrologic model (domain shown in gray) for the period 1950-1997. Source: Mote et al. (2005: Figure 1).

FIGURE 4.18 Linear trends in 1 Apr SWE relative to the starting value for the linear fit (i.e., the 1950 value for the best-fit line): (a) at 824 snow course locations in the western United States and Canada for the period 1950-1957, with negative trends shown by red circles and positive by blue circles; (b) from the simulation by the VIC hydrologic model (domain shown in gray) for the period 1950-1997. Source: Mote et al. (2005: Figure 1).

occurred in, for example, the Southwest, negative trends dominated the region with the largest reductions occurring in western Washington, western Oregon, and northern California.

Accompanying that trend in SWE is a shift in snow melt timing to earlier than average for the contiguous western United States, Alaska, and Canada. Over the period 1966-2007 satellite observations show snow cover reduction over western North America and maritime regions, eastern North America, Scandinavia, and the Pacific coast of Russia (Brown and Mote, 2009).

Predicted Changes in Snow Cover

Snow cover formation and melt are closely related to temperature; therefore snow cover is expected to decrease as temperatures increase. Model results project widespread reductions in snow cover over the 21st century. The Arctic Climate Impact Assessment (ACIA) model mean projects



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