Comparing three land surface schemes used in general circulation models

Land-surface processes are part of the lower boundary conditions for the atmosphere. The schemes used in general circulation models (GCM) to represent this forcing are relatively simple but they play an important role in the simulation of climate. This paper compares three different land-surface schemes used in GCM. All were run with the same imposed atmospheric conditions in order to analyse the differences in the hydrological cycle. The intercomparison showed that simulated evaporation, runoff and soil moisture were different in all three cases. In order to get a better understanding of the mechanisms at work in the models, features from two of the schemes were included in the other scheme. With these modifications we were able to reduce the wide range between model results. We showed that the surface resistance and field capacity were essential parameters in determining the annual cycle of evaporation and that a representation of subgrid-scale variability of soil moisture had an important impact on runoff.