The Implementation and Validation of Improved Landsurface Hydrology in an Atmospheric General Circulation Model

Abstract

New landsurface hydrological parameterizations are implemented into the NASA Goddard Institute for Space Studies (GISS) General Circulation Model (GCM). These parameterizations are: 1) runoff and evapotranspiration functions that include the effects of subgrid scale spatial variability and use physically-based equations of hydrologic flux at the soil surface, and 2) a realistic soil moisture diffusion scheme for the movement of water in the soil column. A one-dimensional climate model with a complete hydrologic cycle is used to screen the basic sensitivities of the hydrological parameterizations before implementation into the full three-dimensional GCM. Results of the final simulation with the GISS GCM and the new landsurface hydrology indicate that the runoff rate, especially in the tropics, is significantly improved. As a result, the remaining components of the heat and moisture balance show comparable improvements when compared to observations. The validation of model results is carried from the large global (ocean and landsurface) scale, to the zonal, continental, and finally the finer river basin scales. (Key words: Climate modeling, Global hydrology)