Climate and Energy Action Plan (CEAP)

CLIMATE TRENDS & PRO JECTIONS | CITY OF ASHLAND, OREGON | FINAL REPORT | 23 Snow pack & Streamflow In the Pacific Northwest, mountain snowpack serves as a natural water reservoir feeding many rivers and streams during the dry seas on (April -September). Historical trends and future projections are presented for April 1 snow water equivalent (SWE), a standard measure of snowpack . Future projections in the monthly hydrograph of total runoff are also presented. Historical Trends Across the western U.S., snowpack declined at about three -fourths of the more than 700 SNOTEL/Snow Course stations. Only a bout a quarter of all stations exhibited statistically significant trends in April 1 SWE, most being decreases (Mote & Sharp, 2014) . The largest decreases in April 1 SWE occurred in Washington, Oregon, and the Northern Rockies ; in contrast, the southern Sierra Nevada in California exhibited increases in snowpack. Ave raged over all sites , the average change in April 1 SWE over the period 1 955-2013 was a 14% decline (Mote & Sharp, 2014) . In the Rogue Basin, a lmost all stations exhibited decreasing trends in April 1 SWE from 1960 to 2014 . The trend was statistically significant at only one site: the Diamond Lake SNOTEL site at an elevati on of about 5,300 feet at the northern end of the Upper Rogue sub -basin had a significant trend in which April 1 SWE declined by 59% (see Figure 16). Trends at all other stations, except the Siskiyou Summit Snow Course in the Midd le Rogue, were negative , ranging from a decrease of 3% to a decrease of 60% (see Table 4). Siskiyou Summit had a positive, though not significant, trend in April 1 SWE amounting to a 100% increase over the period of record ; howeve r, the mean SWE is so small (4 inches) at that location that a small absolute increase resulted in a large relative change.