Evapotranspiration from Irrigated Agriculture and Phreatophyte Shrubs in Nevada, and Role of Surface and Groundwater Interactions on Projected Baseflows in Snow Dominated Regions

Abstract

Assessments of water resources are becoming more important as population grows and climate warms in the western U.S. and beyond. Accurate assessment of current and future water resources relies on accurate estimation of the water and energy budget component of evapotranspiration, ET. In this research, a method is adapted and refined to update irrigated agriculture ET and irrigation water requirement estimates for Nevada using recently published standardized methods and detailed soil water balance accounting. Estimates of irrigated agriculture ET and irrigation water requirements are made for several crop types throughout Nevada to evaluate the spatial distribution and magnitude of irrigation water requirements. Additionally, a complementary relationship approach based on near surface boundary layer feedbacks derived from changes in humidity and temperature is applied to estimate ET from phreatophyte shrubs. A combined total of ten years of micrometeorological data collected over phreatophyte shrubs in eastern Nevada are used to evaluate the complementary relationship and refine the approach. Assessing climate change impacts on surface and groundwater interactions in snow dominated watersheds is of great importance for evaluating future water supplies for development and agriculture in Nevada and the western U.S. An integrated surface and groundwater model was constructed for three snow dominated watersheds tributary to Lake Tahoe and Truckee Meadows, Nevada and California, and Global Climate Model (GCM) projections of temperature and precipitation from six different GCM and two carbon emission scenarios are used to develop ensemble predictions of hydrologic impacts, while specifically focusing on impacts to groundwater and surface water interactions. Results of this work indicate that simple and robust models can estimate ET with reasonable accuracy, and a better understanding of climate change impacts on baseflows can be obtained through the use of integrated surface and groundwater models