Water supply problems in the Middle Río Grande are increasing as New Mexico’s population grows and new demands are placed on finite amounts. Policy and decision makers require tools, such as hydrologic models, to assist in the management of water resources. To exacerbate the problem, anticipated variations induced by global warming will have an uncertain impact on water resources. In this work, we develop and test a semi-distributed watershed model for simulating hydrologic conditions in semiarid river basins. The model is applied to the Río Salado and tested at the point, regional and basin-scales using a range of different atmospheric forcings and a set of plausible climate change scenarios. The model performed well at simulating point-scale soil moisture and gave plausible results for other hydrological variables at the scale of different Hydrologic Response Units (HRUs). Reproducing historical streamflow in the Río Salado with the model was difficult due to an underestimation of high elevation precipitation in the basin. Nevertheless, forcing the model with stochastically-generated, coarse precipitation fields showed improved results during long-term simulations. More importantly, the climate change scenarios demonstrate the usefulness of the semi-distributed watershed model as a tool for assessing hydrologic impacts of seasonal precipitation and temperature changes.