Precipitation, soil, and evaporation validation of the Coupled Hydrosphere-Atmosphere Model

The Coupled Hydrosphere-Atmosphere Research Model (CHARM) is a nested regional climate model for the Great Lakes Basin. Its aim is to simulate climatic conditions and scenarios in the region with an emphasis on water resource output variables. Validation of CHARM, driven by historic lateral boundary conditions, against observed basic climatic variables in the historic record will be presented. One change from CHARM's basis in the Regional Atmospheric Modeling System that has influenced its validation is a change in the surface evapotranspiration scheme that eliminates the spurious persistence of fog. The fog is a very persistent feature of the model that affects the planetary albedo enormously, resulting in reduced near-surface air temperatures and suppressing convective and even stratiform precipitation. Another change is one in the soil model that reduces the amount of surface runoff. This allows more water to infiltrate into the ground and thus increases the evaporative fraction, which in turn causes a slight increase in precipitation, bringing the result closer to the observed.