CALIBRATING GROUNDWATER MODELS TO ESTIMATE THE IMPACTS OF FUTURE CLIMATE CHANGE ON WATER RESOURCES IN THE AMERICAN SOUTHWEST

Models of future climate change predict large increases in temperature and major decreases in precipitation in arid regions worldwide. As water resources are severely limited in many of these environments, the predicted droughts and extreme heat episodes are thought to cause large declines in water resources. However, in order to predict the impact of potential climate changes on water resources, it is necessary to employ sophisticated groundwater models that can quantify the impact of predicted climate changes. In the Death Valley region, several groundwater models have been constructed in conjunction with Yucca Mountain test project over the past 20 years. The early models from the 1980’s were simplified 2-dimensional, finite element models, but the most recent models are 3-dimensional representations of the hydrogeologic framework and groundwater flow systems. The modern models are highly detailed, and have a large range of applicability, from following contaminant flowpaths to analyzing the effects of water depletion caused by pumping. My work is to test these models of the American Southwest, to see if reproducing the known hydrologic conditions during the Last Glacial Maximum (~20,000 ka) is possible. Geologic data for the American Southwest is readily available, and the paleoclimate of the LGM is well known. Since the LGM climate of the American Southwest is well constrained, this is a good area to test the accuracy of these hydrologic models. The modeled paleoclimate results are compared to the accepted paleoclimate data (based on paleoproxies), and the accuracy of the model is determined.

Paleoproxies such as wetland deposits, packrat middens, and paleolakes allow for an assessment of the temperature, precipitation, and recharge rates that would account for the apparent high ancient water table. I will simulate conditions at several localities, in order to verify that that model parameters change by similar amounts for each locality, which will also help to prove that the model functions correctly. With a calibrated and functioning model, it is possible to extrapolate the data towards a future climate setting. As economic growth and climate change will continue to occur, it will allow for future predictions of available water and changes to the potentiometric surface.