Most hydrologic models have been formulated to simulate the runoff and/or storm and base streamflow using point data such as rainfall as input. These models are also normally calibrated with streamflow data, which represent the integration of many of the processes to the basin scale. Therefore, often evapotranspiration (ET) is the residual term or is derived with very simple empirically-based approaches (e.g., Doyle, 1990). Furthermore, the moisture storage in the soil layers computed by these models often are one-dimensional and are not usually validated with observations. On the other hand, there have been efforts to utilize satellite and digital terrain data in hydrologic modeling at the mesoscale (Schultz, 1993), and thus move towards a three-dimensional representation of hydrological processes. Below are some examples where attempts have been made to improve hydrologic models by incorporating more realistic land-surface schemes and spatial information such as surface soil moisture from remote sensing (Engman, 1991).