Assessing the Effects of Climate Change on Middle Rio Grande Surface Water Supplies Using a Simple Water Balance Reservoir Model

The Middle Rio Grande is a vital source of water for irrigation in the region. Climate change is impacting regional hydrology and is likely to put additional stress on a water supply that is already stretched thin. To gain insight on the hydrologic effects of climate change on reservoir storage, a simple water balance model was used to simulate the Elephant Butte-Caballo reservoir system (Southern New Mexico, USA). The water balance model was forced by hydrologic inputs generated by 97 climate simulations derived from CMIP5 Global Climate Models, coupled to a surface hydrologic model. Results suggest the percentage of years that reservoir releases satisfy agricultural water rights allocations over the next 50 years (2021-2070) will decrease compared to the past 50 years (1971-2020). The modeling also projects an increase in multi-year drought events that hinder reservoir management strategies to maintain high storage levels. In most cases, changes in reservoir inflows from distant upstream snowmelt is projected to have a greater influence on reservoir storage and water availability downstream of the reservoirs, compared to changes in local evaporation and precipitation from the reservoir surfaces.