Since OCAR3 (Dalton et al. 2017), a new analysis of observed changes in snow resources in the west (Mote et al. 2018) show that nearly every location in Oregon experienced declines in spring snowpack since mid-20th century.

Recently, an analysis of atmospheric variability (Siler et al 2018) indicates that the influence of regional warming on the west’s snowpack since 1985 has been largely masked by natural variability in ocean temperatures and atmospheric circulation patterns important during the cool season, effectively slowing the rate of spring snowpack decline.

Snow + Water Supply

The authors expect greatly enhanced response in the snowpack to warming in coming decades as this pattern ebbs. The climate toolbox depicts how the region’s water variables will change. For example, Figure 6 shows the disappearing snowpack expected by the end of the century. Most of the Northwest will see decreases in April 1 snowpack in excess of 56% but the highest peaks in the Cascades are projected to decrease less, only in the 11-33% range.

These reductions in snowpack will lead to wintertime increases but summertime decreases in soil moisture in most places (Figure 6). The increases in soil moisture in the driest parts of the region are also seen in the regional superensemble, and are confined to lower soil layers. Upper soil layers also dry substantially there, but the paucity of deep-rooted plants limit the depletion of lower soil layers.

In most basins, the changes in snowmelt timing also alter streamflow (Figure 7). The increases in average wintertime flow (owing to reduced snow accumulation and more rapid runoff) also correspond to increases in flood risk in those basins. Summertime flow is reduced in many basins, by as much as 50% (in June).