Potential influence of climate change in the water budget variables related to the conjunctive use in the Transboundary Rio Grande

Changes in population and agricultural development are increasing demands on available water resources in the Transboundary Rio Grande (TRG), an area defined by the Rio Grande River and the Mesilla aquifer between New Mexico, Texas, and Mexico. Due to the continued drought, surface water availability is continuously declining, increasing the reliance on groundwater to satisfy the water demands (mainly for agriculture and domestic uses). To simulate the conjunctive use and management of the surface water and groundwater in the TRG, a groundwater flow model implemented on Modflow-OWHM called the Rio Grande Transboundary Integrated Hydrologic Model (RGTIHM) has been previously developed. In this study, the RGTIHM model is used to assess the historical conditions and to project climate change driven scenarios on the water budget variables related to conjunctive use of surface water and groundwater in the TRG. The historical conditions were simulated from 1940-2014, while the future scenarios were simulated for the period 2015-2065 considering: i) inputs of precipitation and temperature from global climate change models, ii) management scenarios of land use and water demands for agriculture. The historical period of the model shows that due to the aquifer depletion, the river is permanently becoming a losing stream and at the same time is becoming a source of recharge for aquifer storage, the recharge from irrigated fields has a significant weight in the total recharge, and the diffuse recharge from precipitation is a small source compared to the previous two. The future period shows that maximum and minimum temperatures tend to increase, as well as the real evapotranspiration; precipitation does not change significantly, diffuse recharge decreases, and runoff increases. Water availability in the Rio Grande River decreases due to reduced snowpack in the Rocky Mountains, increasing the reliance on groundwater and posing uncertainty in future water supply management in the TRG.