Incorporation of physical hydrology in a land-surface process model for climate modeling.

There is a need to improve hydrology in land-surface process models for weather and climate modeling. In this study, physical runoff processes were added to the Biosphere-Atmosphere Transfer Scheme (BATS). Runoff is important in both global modeling and regional impact analyses. It impacts soil moisture distribution and feeds back to the atmosphere through its influence on the moisture and energy budgets. General circulation models (GCM's) do not incorporate wetlands and small lakes into their radiation and moisture budgets. These ecosystems have been shown to affect the regional precipitation pattern that GCM's try to reproduce. Hortonian overland flow and the "variable contributing area" concept were incorporated into BATS in a model called BATS/HYDRO. Precipitation that reaches the surface is stored in surface detentions (puddles). When the maximum storage is exceeded, sheet flow commences. Water is routed through a hierarchy of channels to the edge of the grid cell where it is considered surface runoff. Overland and return flow are functions of terrain, vegetation type and soil type. The saturated area of the grid cell is calculated by assuming soil moisture is normally distributed. Return flow is calculated to exit the ground in saturated areas, and saturation overland flow is produced when precipitation falls on saturated areas. BATS/HYDRO has been developed further by coupling overland flow horizontally into a three-dimensional land-surface model, BATS3D. The models were tested on the Saline River in Southeast Lower Michigan, a temperate watershed. It contains extensive wetlands and shows the feasibility of using the models on similar watersheds. Daily streamflow observations for the Saline River were compared with runoff from the models. The influence of subgrid-scale heterogeneity and runoff routing on smaller grid size were also investigated to determine the model's accuracy. The physical hydrology in BATS/HYDRO and BATS3D produced more realistic runoff than BATS. This, in turn, increased the soil moisture and latent heat flux eliminating the summer dryness problem inherent in BATS.PhDAtmospheric and Space SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/104609/1/9542822.pdfDescription of 9542822.pdf : Restricted to UM users only