ON THE SIMULATION OF INFILTRATION-EXCESS AND SATURATION-EXCESS RUNOFFUSING RADAR-BASED RAINFALL ESTIMATES - EFFECTS OF ALGORITHM UNCERTAINTY AND PIXEL AGGREGATION

The effects of uncertainty in radar-estimated precipitation input on s imulated runoff generation from a medium-sized (100-km(2)) basin in no rthern Texas are investigated. The radar-estimated rainfall was derive d from Next Generation Weather Radar (NEXRAD) Level II base reflectivi ty data and was supplemented by ground-based rain-gauge data. Two type s of uncertainty in the precipitation estimates are considered: (1) th ose arising from the transformation of reflectivity to rainfall rate a nd (2) those due to the spatial and temporal representation of the ''t rue'' rainfall field. The study explicitly differentiates between the response of simulated saturation-excess runoff and infiltration-excess runoff to these uncertainties. The results indicate that infiltration -excess runoff generation is much more sensitive than saturation-exces s runoff generation to both types of precipitation uncertainty. Furthe rmore, significant reductions in infiltration-excess runoff volume occ ur when the temporal and spatial resolution of the precipitation input is decreased. A method is developed to relate this storm-dependent re duction in runoff volume to the spatial heterogeneity of the highest-i ntensity rainfall periods during a storm.