Climate Change Impacts on Municipal Water Management in El Paso, Texas

Municipal water supplies for the City of El Paso include both surface water and groundwater, which are conjunctively managed: when surface water supplies are reduced due to drought conditions, groundwater pumping is increased in order to meet demands.  Water planners in the region have always understood the nature and consequences of climatic variability on managing water supplies.  Considerable investments have been made to assure adequate supplies under a wide range of climatic conditions.  This investigation assessed the vulnerability of El Paso’s municipal water supplies to historic variation of regional climate as well as to the consequences of predictions in the 2007 Intergovernmental Panel on Climate Change (IPCC) report. 
Runoff from northern New Mexico and southern Colorado represents the majority of Rio Grande flow that feeds Elephant Butte Reservoir, the major regulating reservoir for the area.   Based on the tree-ring data, annual inflow to Elephant Butte Reservoir was simulated for 1007 years (1001 to 2007).  These simulated inflows show that 50-year average Elephant Butte inflow has varied from about 600,000 AF/yr to over 1,200,000 AF/yr.  Current 50-year average inflow is about 800,000 AF/yr. 
This investigation included simulating 60 scenarios of various precipitation and reservoir evaporation conditions based on the historic variability and changes to historic variability based on IPCC predictions.  Due to limitations associated with GCMs in mountainous terrain, predictions range from a 25% decrease in precipitation to a 10% increase in precipitation.  Each of the 60 scenarios included 958 50-year simulations, for a total of 57,480 50-year simulations.  Based on the analysis, future demands can be met with the current infrastructure and under the current management approach though the year 2060 under all scenarios.  This analysis highlights the effectiveness of past investments made in water infrastructure and the efficacy of the current management approach to respond to climatic variability.