Estimating future runoff levels for a semi-arid fluvial system in central Arizona, USA

ABSTRACT: We developed a water budget runoff model for the Salt and Verde River basins of central Arizona and used the outputs of 6 global climate models (GCMs) to estimate runoff in the future under assorted emissions scenarios developed by the Intergovernmental Panel on Climate Change (IPCC). We used a statistical downscaling routine to refine the GCM outputs for the 2 basins, and we found that all model–scenario combinations simulate a mean temperature rise in the study area of between 2.4 and 5.6°C, using year 2050 greenhouse gas concentrations. Mean changes in precipitation vary substantially among the models and scenarios, and, as a result, changes in runoff vary from 50 to 127% of historical levels. Assuming equal probabilities associated with each scenario and model run, the overall results suggest that runoff from the Salt and Verde will have an approximately 85% chance of being less strong, the certainty of which is related to consensus on warming in the study area. The large variability among predictions of precipitation trends introduces substantial uncertainty.