Abstract

The hydrologic response of eight headwater catchments located at and above the rain-snow transition, 1,500-2,500 m elevation, was investigated over five years using hourly streamflow, precipitation, snowpack and weather-station data. The Kings River Experimental Watersheds (KREW) is a watershed-level, integrated ecosystem project for long-term research on nested headwater streams in the southern Sierra Nevada. The four lower elevation watersheds also comprise the Southern Sierra Critical Zone Observatory. Water yield increased and retention decreased with elevation consistently for all years, but the form of the relationship was distinctly different for the wet years (2005 and 2006) when compared to the dry years (2004 and 2007). Stream base flows range from less than 1 to 10 liters per second (l/s), but during spring snowmelt flows of 400 l/s occur for a month or more. Maximum peak flows of more than 1,000 l/s were measured for a single rain event. While the amount of precipitation is similar for all watersheds, about 40 percent leaves the lower elevation watersheds as stream discharge compared to 60 percent for the higher elevation watersheds. The lower elevation watersheds are representative of how the higher watersheds may function with climate change. The rain-snow transition zone in these forested, mountain catchments undergoes dramatic seasonal changes, going from a snow-covered, water-saturated state with modest evapotranspiration (ET) to a system dominated by ET to a relatively dry state over a period of only a few weeks. The spring runoff period typically lasts from March to May at the lower elevation site. Runoff consistently lags about one month across this elevation range, with interannual variability also accounting for a 1-month difference in timing. Snowmelt occurs over a period of about one month in higher-elevation catchments, followed by a 2-week-long transition to evapotranspiration dominance of streamflow. Lower-elevation catchments are rainfall-dominated in spring, with the transition to evapotranspiration dominance being less distinct. Lags in the system between peak temperature and peak snowmelt were consistent at about 10 hours; the summer lag between solar maximum and streamflow minimum was similar, but offset.

Citation

Hunsaker, C., Bales, R. (2008): Water Yield and Runoff Timing Across the Rain-snow Transition at the Kings River Experimental Watersheds in Californias Southern Sierra Nevada. Fall meeting, American Geophysical Union, December 2008. 89(53). Abstract 13C-0933.