SiB2 of Sellers et al. (1996) was used in the land surface sub-model. In SiB2, satellite data was used to describe the vegetation phenology of a given DBHM grid area. A realistic canopy photosynthesis- conductance model was incorporated to describe the simultaneous transfer of CO2 and water vapor into and out of the vegetation. The hydrological part of the SiB2 simulated the surface runoff of the given DBHM grid area and calculated the interlayer exchanges within the soil profile and interaction between soil water and groundwater.
The hydrological sub-model is based on geomorphological characteristics of the river basin to modeling the surface and subsurface flow, mainly using DEM-based methodologies developed by hydrologists (Yang et al., 1998; Verdin and Verdin, 1999).
The surface runoff flowing to a river system was described by one dimensional kinematic wave model (Lighthill and Whitham, 1955; Chow, 1959). An approach from Rushton and Tomlinson (1979) was used to estimate groundwater and river water interaction. Realistic watershed map and river way map were used to delineate sub-river basins and river network. The sub-river basins were coded following Pfafstetter method (Verdin and Verdin, 1999; Pfafstetter, 1989). The runoff was then accumulated and routed to outlet using kinematic wave approach.
The incorporation of land surface model SiB2 with its most critical processes, evapotranspiration, derived from satellite observations and heat flux simulation in the SVAT processes represents the major improvement in DBHM over other distributed hydrological models. Subsequent sections provide the details of the DBHM.