A distributed model for estimation of runoff volumes and peak rates of flow from small semiarid watersheds is shown to produce reasonable estimates for mean runoff and flood frequency distributions. The model is simplified and constructed to require a minimum of observed data for calibration. The model simulates runoff volume and peak discharge rates for individual storm events. It can also be used to estimate water yield and a surface water balance incorporating transmission losses in ephemeral stream channels. Experimental data are compared with the simulation model predictions. Individual components of the model could be improved with further research and data. However, based on available information contained in soils and topographic maps and published sources, the distributed model can be used to estimate runoff rates and amounts from ungaged watersheds in semiarid regions.