Using a global soil wetness dataset to improve seasonal climate simulation

Ensembles of boreal summer coupled land-atmosphere climate model integratio ns for 1987 and 1988 are conducted with and without interactive soil moistu re to evaluate the degree of climate drift in the coupled land-atmosphere m odel system, and to gauge the quality of the specified soil moisture datase t from the Global Soil Wetness Project (GSWP). Use of specified GSWP soil m oisture leads to improved simulations of rainfall patterns, and significant ly reduces root-mean-square errors in near-surface air temperature, indicat ing that the GSWP product is of useful quality and can also be used to supp ly initial conditions to fully coupled climate integrations. Integrations u sing specified soil moisture from the opposite year suggest that the intera nnual variability in the GSWP dataset is significant and contributes to the quality of the simulation of precipitation above what would be possible wi th only a mean annual cycle climatology of soil moisture. In particular, sp ecification of soil wetness from the wrong year measurably degrades the cor relation of simulated precipitation and temperature patterns compared to ob served.