The relationship between catchment rainfall, evapotranspiration and runoff can be exploited to assess climate risk to water resources. National data regarding climatology and runoff were used to estimate the sensitivity of regional runoff to projected changes in precipitation and evaporation. These sensitivity factors were integrated with patterns of climate change from 12 different global climate model (GCM) simulations to project future annual runoff sensitivity per degree of global mean temperature change. Divergent runoff sensitivities were identified depending upon the selected GCM. Averaging among GCMs resulted in a robust pattern of runoff sensitivity suitable for estimating future climate risk.