Effect of the number of soil layers on a modeled surface water budget

A sensitivity analysis was performed to determine the effects of systematic ally increasing the number of soil layers in a land surface-atmosphere mode l on the components of the modeled water budget. The study was done for a f orested location in central Oklahoma for a 65-day period in spring 1996 usi ng the model called Simulator for Hydrology and Energy Exchange at the Land Surface (SHEELS). SHEELS is based on the Biosphere-Atmosphere Transfer Sch eme (BATS), except that the subsurface hydrology was substantially changed to improve representation of the soil moisture profile. The soil profile wa s divided into zones of thickness 0.05 m (upper), 1.25 m (root), and 1.20 m (bottom). The two principal conclusions are that (1) the water budget is v ery sensitive to the number of layers in the soil profile under wet conditi ons and (2) the water budget is much more sensitive to the number of layers in the profile than to the range of 2 orders of magnitude in saturated hyd raulic conductivity considered in this study. A result of the latter conclu sion is that larger errors in modeled water fluxes can occur From using an insufficient number of soil layers than from using an incorrect value of sa turated hydraulic conductivity.