Soil moisture in a regional climate model: simulation and projection

Regional climate simulations driven by three sets of initial and lateral boundary conditions - analyzed observations, GCM control climate, and GCM enhanced greenhouse-gas scenario climate - are used to assess model accuracy in predicting soil moisture and to examine changes in soil moisture in the scenario climate. Simulated soil moisture does not show noticeable drift during the 10-year simulations. Observed and simulated soil moisture for Illinois 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 than observed, at least in part due to underprediction of precipitation in autumn. This suggests that improvements in simulating soil moisture depend greatly on improvements in simulating precipitation. The climate change scenario 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 wetter in all seasons.