20th century trends in runoff, evapotranspiration, and soil moisture in the Western U.S
Hamlet, A.F., P.W. Mote, M.P. Clark, and D.P. Lettenmaier. 2007. 20th century trends in runoff, evapotranspiration, and soil moisture in the Western U.S. Journal of Climate 20(8): 1468-1486. DOI: 10.1175/JCLI4051.1
A physically based hydrology model is used to produce time series for the period 1916-2003 of evapotranspiration (ET), runoff, and soil moisture (SM) over the western United States from which long-term trends are evaluated. The results show that trends in ET in spring and summer are determined primarily by trends in precipitation and snowmelt that determine water availability. From April to June, ET trends are mostly positive due primarily to earlier snowmelt and earlier emergence of snow-free ground, and secondarily to increasing trends in spring precipitation. From July to September trends in ET are more strongly influenced by precipitation trends, with the exception of areas (most notably California) that receive little summer precipitation and have experienced large changes in snowmelt timing. Trends in the seasonal timing of ET are modest, but during the period 1947-2003 when temperature trends are large, they reflect a shift of ET from midsummer to early summer and late spring.
UW Climate Impacts Group