Spatial Variability in Hydrologic Modeling Using Rainfall-Runoff Model and Digital Elevation Model

A rainfall-runoff model based on a digital elevation model was employed for investigation of spatial variability in hydrologic modeling in a small catchment (3 km2) in South Australia. The study improves an existing model, THALES, by further developing the time-variant, spatially distributed watershed moisture representation, and by also developing spatially distributed rainfall as input rainfall data. A time-variant threshold or boundary wetness index is developed as a function of antecedent baseflow of the storms. The boundary wetness index was used to distinguish and represent spatially and temporally variable saturation and nonsaturation areas of a watershed at the beginning of and during a storm. Spatially distributed rainfalls were developed to reduce the impact of single-gauge rainfall on runoff prediction results. The representation of moisture distribution was found to be the most important factor for runoff prediction in this study, while spatial rainfall was the second most important. The study suggests that runoff prediction errors are closely related to the lack of spatial resolution in input data, as well as the lack of effective tools to describe spatial variability, particularly under dry field conditions.