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.