Soil moisture in a regional climate model: simulation and projection

Regional climate simulations driven by three sets of initial and lateral bo undary conditions - analyzed observations, GCM control climate, and GCM enh anced greenhouse-gas scenario climate - are used to assess model accuracy i n predicting soil moisture and to examine changes in soil moisture in the s cenario climate. Simulated soil moisture does not show noticeable drift dur ing the 10-year simulations. Observed and simulated soil moisture for Illin ois and Iowa correspond reasonably well for the top 10 cm soil layer but a consistent low bias is present in the top I in. Growing season depletion of soil water is simulated well but recharge after growing season is slower t han observed, at least in part due to underprediction of precipitation in a utumn. This suggests that improvements in simulating soil moisture depend g reatly on improvements in simulating precipitation. The climate change scen ario produces drier soil in the top 10 cm during winter but wetter top soil in warm seasons because of greater precipitation, while top 1 in soil is w etter in all seasons.