HR: 11:42h
AN: A42A-06    [Abstracts]
TI: Trends in Runoff and Soil Moisture in the Western U.S. from 1915-2003
AU: * Hamlet, A F
EM: hamleaf@u.washington.edu
AF: JISAO CSES Climate Impacts Group, University of Washington, Box 354235, Seattle, WA 98195 United States
AU: * Hamlet, A F
EM: hamleaf@u.washington.edu
AF: Department of Civil and Environmental Engineering, University of Washington, Box 352700, Seattle, WA 98195 United States
AU: Clark, M
EM: clark@vorticity.colorado.edu
AF: Center for Science and Technology Policy Research, University of Colorado Boulder, 488 UCB University of Colorado, Boulder, CO 80309-0488 United States
AU: Mote, P W
EM: philip@atmos.washington.edu
AF: JISAO CSES Climate Impacts Group, University of Washington, Box 354235, Seattle, WA 98195 United States
AU: Lettenmaier, D P
EM: dennisl@u.washington.edu
AF: JISAO CSES Climate Impacts Group, University of Washington, Box 354235, Seattle, WA 98195 United States
AU: Lettenmaier, D P
EM: dennisl@u.washington.edu
AF: Department of Civil and Environmental Engineering, University of Washington, Box 352700, Seattle, WA 98195 United States
AB: Observational studies of snowpack in the western U.S. over the second half of the twentieth century show systematic changes in snow accumulation and melt processes associated with warming temperatures. Studies of long-term changes in streamflow over the same period have found systematic changes in the seasonality of runoff with less runoff occurring in spring and early summer and more runoff in winter later in the period. In previous work we have used reconstructions using a macroscale hydrologic model implemented at 1/8th degree latitude-longitude spatial resolution to examine trends in spring snowpack in the western U.S. for a longer period of record that includes most of the 20th century. The model reconstructions also permit an explicit sensitivity analysis of the separate roles of trends in temperature and precipitation. Here we extend these modeling studies to examine trends in runoff and soil moisture associated with the observed (and reconstructed) changes in snowpack. The Variable Infiltration Capacity (VIC) hydrologic model was forced by a new temporally and topographically adjusted climatological (precipitation and temperature) driving data set from 1915-2003. The hydrologic simulations corroborate the observed trends in streamflow over the West from 1950-present, and show dramatic changes in the seasonality of runoff over large spatial scales, particularly in sensitive intermediate elevation (transient snow zone) areas in Washington, Oregon, and California. Soil moisture also shows systematic trends in summer associated with changes in snowmelt runoff, with summer soil moisture declining in areas that have experienced significant reductions in snowpack and/or earlier snowmelt. Sensitivity analysis shows that these trends are most clearly associated with the changes in temperature over the observed period rather than changes in precipitation.
DE: 1827 Glaciology (1863)
DE: 1860 Runoff and streamflow
DE: 1866 Soil moisture
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting