UC Merced

Differences in hydrologic response across the rain-snow transition in the southern Sierra Nevada were studied in eight headwater catchments - the Kings River Experimental Watersheds - using continuous precipitation, snowpack, and streamflow measurements. The annual runoff ratio (discharge divided by precipitation) increased about 0.1 per 300m of mean catchment elevation over the range 1,800-2,400m. Higher-elevation catchments have lower vegetation density, shallow soils with rapid permeability, and a shorter growing season when compared with those at lower elevations. Average annual temperatures ranged from 6.8°C at 2,400m to 8.6 at 1,950m elevation, with annual precipitation being 75-95% snow at the highest elevations vs. 20-50% at the lowest. Peak discharge lagged peak snow accumulation on the order of 60days at the higher elevations and 20 to 30days at the lower elevations. Snowmelt dominated the daily streamflow cycle over a period of about 30days in higher elevation catchments, followed by a 15-day transition to evapotranspiration dominating the daily streamflow cycle. Discharge from lower elevation catchments was rainfall dominated in spring, with the transition to evapotranspiration dominance being less distinct. Climate warming that results in a longer growing season and a shift from snow to rain would result in earlier runoff and a lower runoff ratio. © 2012 American Water Resources Association.