Landsurface Hydrology Parameterization for Atmospheric General Circulation Models: Inclusion of Subgrid Scale Spatial Variability and Screening with a Simple Climate Model

Prepared under the support of the National Aeronautics and Space Administration. NAG 5-743Parameterizations are developed for the representation of subgrid hydrologic processes in atmospheric general circulation models. Reasonable a priori probability density functions of the spatial variability of soil moisture and of precipitation are introduced. These are used in conjunction with the deterministic equations describing basic soil moisture physics to derive expressions for the hydrologic processes that include subgrid scale variation in parameters. The major model sensitivities to soil type and to climatic forcing are explored offline of the climate model. For more comprehensive sensitivity analyses, a one-dimensional model equipped with GCM physical parameterizations is used. The dynamic heat and moisture convergence are parameterized. The advantages of online sensitivity analyses with this one-dimensional model is that the major model climate landsurface-atmosphere feedbacks are essentially reproduced in this simple GCM analog. The climate model is then used to screen various alternatives and sensitivity simulation experiments