RAIN-INDUCED OUTFLOW FROM DEEP SNOWPACKS IN THE CENTRAL SIERRA-NEVADA, CALIFORNIA

In many mountainous areas of the Pacific coast of North America, rainfall onto snowpacks causes massive floods, probably the single greatest cause of changes in channel morphology and lotic habitats, To understand and model this hydrometeorological phenomenon better, process-response hypotheses were developed for snowpack outflow amount, duration and rate and the time lags from the beginning of rainfall to initial and peak outflow. The hypotheses were evaluated by correlation and regression analyses based on measurements of 20 rain-on-snow events monitored between 1984 and 1990 at forested and open plots near Lake Tahoe, California. Outflow amount correlated significantly with precipitation amount, duration and rate, snow depth and melt potential. Many of these variables also correlated significantly with outflow duration and rate and lag time to peak outflow. Regression models explained 80-90% of the variation in outflow amount and duration. Significant differences were not identified between the forest and open plots for any of the outflow attributes.