The impacts of spatially distributed precipitation and soil heterogeneity on modeling water fluxes at different spatial resolutions are investigated using the VIC-3L (Three-layer Variable Infiltration Capacity) land surface model at the Blue River basin, Oklahoma. In this study, hourly grid-based NEXRAD stage ? radar precipitation data at 4 x 4 km2 resolution are used to obtain daily precipitation at the six different spatial resolutions of 1/32nd, 1/16th, 1/8th, 1/4th, 1/2nd and 1 degree based on an area weighted average method. Soil parameters at the corresponding six spatial resolutions are derived from the STATSGO (State Soil Geographic) data set. The forcing data of daily maximum and minimum temperature, wind speed, and vegetation parameters are disaggregated/aggregated directly to finer/coarser spatial resolutions based on the University of Washington’s data, which are gridded at the 1/8th degree spatial resolution. Our study suggests that a critical spatial resolution for VIC-3L may exist at which finer spatial resolutions do not necessarily result in better model performance in terms of runoff, evapotranspiration, and soil moisture if the model parameters are calibrated at each spatial resolution. Also, model parameters calibrated at a coarse resolution can be applied to finer resolutions to simulate fluxes comparable to those obtained using parameters calibrated at the finer resolutions. However, model parameters calibrated at the finer resolutions cannot be applied to coarse resolution to yield fluxes comparable to those obtained using parameters calibrated at resolutions coarser than the critical spatial resolution. In addition, while soil moisture is more sensitive to the spatial distributions of soil properties, runoff and evaporation are more sensitive to the spatial distributions of precipitation at the watershed being studied.
Revised: February 26, 2009 |
Published: October 31, 2004