Soil moisture simulations in revised AMIP models

Soil moisture is important both in its influence on climate and for assessing impacts of future climate change. It is therefore necessary to simulate it correctly in global climate models. We have used the revisit simulations contributed by six of the Atmospheric Model Intercomparison Project 1 participating modeling groups to examine the impacts of model revisions, particularly the land surface representations, on soil moisture simulations, by comparing the simulations to actual soil moisture observations. The revised models do not show any systematic improvement in their ability to simulate observed seasonal variations of soil moisture over the regions studied. Many of the revised models continue to have a strong tendency toward dry soil conditions during Northern Hemisphere summer months, both globally and regionally. There are no indications of conceptually more realistic land surface representations producing better soil moisture simulations in the revised climate models. As the revised models continue to produce incorrect simulations of the seasonal cycle of regional precipitation, it is not possible to isolate the effect of land surface schemes on the simulations. The European Centre for Medium Range Weather Forecasts and National Centers for Environmental Prediction/National Center for Atmospheric Research reanalyses, however, which are driven by observed precipitation, do capture some of the observed interannual variability of soil moisture over Illinois.