Assessing Potential Implications of Climate Change for Long-Term Water Resources Planning in the Lower Colorado River Basin

摘要

The Lower Colorado River Authority (LCRA) – San Antonio Water System (SAWS)Water Project is being studied to conserve water, develop conjunctive groundwatersupplies, and capture excess and unused river flows to meet future water needs fortwo neighboring regions in Texas. Agricultural and other rural water needs would bemet on a more reliable basis in the lower Colorado River basin through waterconservation, surface water development and limited groundwater production.Surface water would be transferred to the San Antonio area to meet municipal needsin quantities still being evaluated. The project is in its sixth year of detailed studiesaddressing environmental, agricultural, socioeconomic, and engineering aspects ofthe project. Tools are being developed and used in project planning includinginstream flow criteria, water quality assessments, bay freshwater inflow criteria,surface water availability models and operating approaches, agricultural conservationmeasures, groundwater models, and economic models.Models used to calculate water availability and environmental flow requirementshave been developed largely within existing frameworks based on hydrologic dataavailable from historical events. This is a standard approach used by water plannersacross the country as well as by many regulatory agencies for permit review. In viewof the project’s eighty-year planning horizon, contractual obligations associated withthis particular project, comments from the project’s Science Review Panel andincreased public and regulatory awareness of climate change issues, the project teamis exploring predictions of climate change in the region and methods to assesspotential impacts on the LCRA-SAWS Water Project during the project’s expectedlife.After qualitatively assessing system vulnerabilities potentially resulting from changedclimate conditions, the project team initiated a quantitative evaluation of possiblefuture climate scenarios. Using a scenario approach identifies a broad range ofpossible future implications for the watershed and its various systems. Twoatmosphere-ocean general circulation models and two carbon emission scenarioswere selected from which to generate potential climate scenarios for future timeperiods of 2050 and 2080. Global-scale changes in key climate parameters (i.e.,temperature, precipitation, evaporation and sea level rise) were then translated to thelocal watershed scale. The Variable Infiltration Capacity hydrology model was thenused to simulate historical runoff, river flow and evaporation under future climate