Abstract - RegCM2 & Hydrology

 

Hay, L.E., M.P. Clark, R.L. Wilby, W. J. Gutowski Jr., R. W. Arritt, E. S. Takle, Z. Pan and G.H. Leavesley, 2002: Use of regional climate model output for hydrologic simulations. J. Hyrdometeor. (in press).

Daily precipitation and maximum and minimum temperature time series from a Regional Climate Model (RegCM2) configured using the continental U.S. as a domain and run on a 52 km (approximately) spatial resolution w ere used as input to a distributed hydrologic model for a rainfall-dominated basin (Alapaha River at Statenville, Georgia) and three snowmelt-dominated basins (Animas River at Durango, Colorado; East Fork of the Carson River near Gardnerville, Nevada; and Cle Elum River near Roslyn, Washington). For comparison purposes, spatially averaged daily data sets of precipitation and maximum and minimum temperature were developed from measured data for each basin. These data sets included precipitation and temperature data for all stations (All- Sta) located within the area of the RegCM2 model output used for each basin, but excluded station data used to calibrate the hydrologic model.

Both the RegCM2 output and All-Sta data capture the gross aspects of the seasonal cycles of precipitation and temperature. However, in all four basins, the RegCM2- and All-Sta-based simulations of runoff show little skill on a daily basis (Nash- Sutcliffe (NS) values range from 0.05-0.37 for RegCM2 and -0.08-0.65 for All-Sta). When the precipitation and temperature biases are corrected in the RegCM2 output and All-Sta data (Bias-RegCM2 and Bias-All, respectively) the accuracy of the daily runoff simulations improve dramatically for the snowmelt-dominated basins (NS values range from 0.41-0.66 for RegCM2 and 0.60-0.76 for All-Sta). In the rainfall-dominated basin, runoff simulations based on the Bias-RegCM2 output show no skill (NS value of 0.09) whereas Bias-All simulated runoff improves (NS value improved from -0.08 to 0.72).

These results indicate that measured data on the scale of the resolution of the RegCM2 output can be made appropriate for basin-scale modeling through bias correction (essentially a magnitude correction). However, RegCM2 model output, even when bias corrected, does not contain the day-to-day variability present in the All-Sta data set that is necessary for basin-scale modeling. Future work is warranted to identify the causes for systematic biases inRegCM2 simulations, develop methods to remove the biases, and improve RegCM2 simulations of daily variability in local climate.