Snowpack and Streamflow Trends in the Cascade Mountains of Northern Washington, USA and Southern British Columbia, Canada
Abstract
Most studies of snowpack trends focus on the snow water equivalent (SWE) measured at snowcourses on or near 1 April. Although these data are generally the longest time series of SWE available in North America, the single measurement per year misses other behaviors of the snowpack, which may be as sensitive or even more sensitive indicators of the effects of climate change and global warming. Daily SWE data from automated snow pillows can be used to assess trends in these other behaviors, such as the peak SWE and the date of its occurrence, the date of initiation of permanent winter snowpack, and the date of melt out. Although the time series available for daily SWE measurements are of significantly shorter duration than the 1 April snowcourse measurements (20-30 years rather than 70-80), it is nevertheless worth looking at the snowpack characteristics that can be derived from daily data to see what trends can or cannot be seen. Such analyses were carried out for a few selected sites from the USDA Natural Resources Conservation Service SNOTEL network and the British Columbia automated snow pillow network in the Cascade Mountains of northern Washington and southern British Columbia. Trends for the four quantities mentioned above (peak SWE, date of peak SWE, date of initiation of permanent winter snowpack, and date of melt out) were examined. Although most of the trends were not statistically significant due to the short record lengths and high degree of variability, they were generally what one would expect in a warming climate, such as later initiation of winter snowpack and earlier date of peak SWE. A simple analysis of streamflow timing was also carried out to see if these trends were consistent with the snowpack trends. The analysis was carried out on five rivers, three on the east side of the Cascades and two on the west side, all of which have their headwaters in the same vicinity of the snow sites analyzed. The quantity examined was the monthly fraction of total water year flow. These were computed as time series, and changes in behavior were noted over time. These data were also grouped according to Pacific Decadal Oscillation (PDO) eras, and average monthly fractions for each era were computed. The primary trend noted was an increase in the winter (November-January) flow fraction and an increase of the March fraction coupled with a decrease in the April fraction. There was also a notable difference in flow fractions between the two warm PDO eras represented in the time series (1925-1946 and 1977-2008) in that the current warm PDO era has had more flow in the winter and early spring than did the previous PDO warm era, suggesting that the current PDO warm era is different from (warmer than) the previous one.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.C21A0506G
- Keywords:
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- 0740 Snowmelt;
- 1807 Climate impacts;
- 1860 Streamflow;
- 1863 Snow and ice (0736;
- 0738;
- 0776;
- 1827)