HR: 0800h
AN: C31A-0304    [Abstracts]
TI: A comparison of physically based and degree-day representations of snowpack / atmosphere turbulent fluxes in an alpine watershed
AU: Jacobson, P
EM: pjacobson@colorado.edu
AF: Department of Geological Sciences, University of Colorado, Boulder, 399 UCB, Boulder, CO 80309-0001 United States
AU: * Molotch, N P
EM: molotch@cires.colorado.edu
AF: Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, 216 UCB, Boulder, CO 80309-0216 United States
AU: Bales, R C
EM: rbales@ucmerced.edu
AF: Division of Engineering, University of California, Merced, P.O. Box 2039, Merced, CA 95344 United States
AU: Colee, M T
EM: mtc@icess.ucsb.edu
AF: Donald Bren School of Environmental Science and Management, University of California, Santa Barbara, Bren Hall, Santa Barbara, CA 93106 United States
AU: Dozier, J
EM: dozier@bren.ucsb.edu
AF: Donald Bren School of Environmental Science and Management, University of California, Santa Barbara, Bren Hall, Santa Barbara, CA 93106 United States
AB: The degree-day turbulent flux algorithm of the Snowmelt Runoff Model (SRM) was compared with a physically based turbulent flux algorithm to evaluate the trade-offs between model complexity, data input intensity and model accuracy. The two different turbulent flux representations were used in a snowpack mass and energy balance model that explicitly represents net radiation. Snowmelt simulations were coupled with a time-series of remotely sensed snow covered area (SCA) data to simulate daily snowmelt volume in the 19.1-km$^{2}$ Tokopah Basin of the southern Sierra Nevada, California. Modeled daily snowmelt rates for each 30-m pixel were scaled by the SCA and integrated over the snowmelt season to obtain estimates of maximum SWE accumulation. Evaluation of model performance using remotely sensed snow covered area indicated that snow cover depletion rates were reasonably simulated using the physically based model but were overestimated using the degree-day model, with total snow disappearance occurring at least 16 days prior to observed disappearance. Un-calibrated correlations between modeled basin-wide snowmelt volume and observed runoff indicated that the timing of snowmelt was simulated adequately with the degree-day model (R$^{2}$ = 0.59) relative to the physically based model (R$^{2}$ = 0.62). Modeled peak snowmelt occurred 18 days prior to peak observed runoff in both cases. Results from a regression tree and co-kriging interpolation of 397 snow depth observations obtained at maximum SWE were compared with the maximum SWE reconstructions from the snowmelt models. Model SWE reconstruction error was 36 percent for the degree-day model versus 12 percent for the physically based model. Relative to the physically based model, the degree-day model was able to adequately represent the timing of snowmelt with a significantly lower computational and input data requirement.
DE: 1800 HYDROLOGY
DE: 1836 Hydrologic budget (1655)
DE: 1863 Snow and ice (1827)
DE: 1878 Water/energy interactions
DE: 1884 Water supply
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting