Impacts of GCM predictions of climate change on water resources in the Upper Brazos River watershed

Climate models of earth-atmosphere interactions on a global scale are the most prominent among the approaches used by researchers to understand global climate change. Atmospheric models, termed General Circulation Models (GCMs), are currently used to model the entire globe on sub-hourly time scales with spatial scales of several degrees latitude and longitude. The computational grid scale used by GCMs is much larger than most watersheds. Therefore, means to transfer the large scale results from GCMs to the smaller watershed scale were required. This scale problem was compounded by the fact that GCM results for current climate conditions deviate from measurements made at ground stations. An approach was developed to statistically describe the predicted climate change and adjust the statistics of observed meteorologic data. A stochastic model was developed to simulate the observed meteorologic variables under current climatic conditions. Statistical analysis of the GCM output was used to indicate the magnitude and direction of change that might occur under doubled CO₂ conditions.; A hydrologic model was developed for the Upper Brazos River watershed in northwest Texas. The hydrologic model was calibrated using measured climatic data and used to simulate conditions resulting from doubled CO₂ conditions. The results of the changed climate conditions were compared to the existing climate results to assess the impacts of climate change on the water supply in the basin.