Submitted to: European Geosciences Union General Assembly Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: November 1, 2007
Publication Date: December 8, 2007
Citation: Marks, D.G., Nayak, A., Chandler, D., Winstral, A.H. 2007. Long-term trends in snow and hydro-climatic parameters over a mountainous catchment in the western united states. Presented in Joint Symposium JHW002: Climate-Permafrost-Hydrology Interactions: The Impact of Changing Climate on Cold Regions Hydrology, The 24th General Assembly of teh IUGG, Perugia, Italy, July 2-13, 2007. Technical Abstract: Numerous investigators have reported changes in patterns of snow deposition and melt in the western US. The Reynolds Creek Experimental Watershed (RCEW) provides us the opportunity to evaluate these changes by looking at 45 years (1960-2005) of data from multiple measurement locations representing different elevation and site conditions. In this study we analyze the data from the three long term weather sites established in 1960’s and investigate the trends present in snow, hydro-climatic parameters (air temperature, humidity, precipitation (total volume and rain vs. snow)) and streamflow on a daily, monthly, seasonal and annual basis, over the period of data records. Analysis shows that while there are no significant trends in total water year precipitation or stream discharge, summer flows have been reduced by as much as 27% with corresponding increases in winter and early spring flows. Temperature data show that over the period of record there has been an increase in water year average daily temperature of 1.2 C at the lower, 1.8 C at the mid- and 2.4 C at the high elevation sites. This is characterized by a larger increase in average daily minimum temperature at the low and mid-elevation sites. While precipitation has not changed, the mix of rain and snow has shifted strongly toward more rain and less snow, showing a 22% decrease (from 41% to 19%) at the low, a 17% decrease (from 55% to 38%) at the mid- and a 16% decrease (from 80% to 62%) at the high elevation site. This indicates that the higher elevations are still snow dominated, that the mid-elevations still get snow, but are now rain-dominated, and that the low elevations now seldom get snow. Analysis of SWE data from eight sites sampled bi-weekly during the period of record shows a decrease in peak SWE, and a movement of peak SWE to nearly a month earlier at all sites. This study shows that there have been changes with statistically significant trends in snow and hydro-climatic parameters in mountain watersheds in North America, and that those trends have a strong elevation effect. If they continue, we can expect that the most significant impacts will occur at lower elevations, reduced summer streamflow, and increased winter rain. These results also illustrate the value of high quality, long-term data from experimental watersheds in understanding the potential impacts of global warming on water resources.