Overconsumption gravely threatens water security in the binational Rio Grande-Bravo basin

The Rio Grande-Bravo basin shared by the United States and Mexico is experiencing a severe water crisis demanding urgent attention. In recent decades, water storage reservoirs, aquifers, and annual streamflow volumes have been substantially depleted, leaving little buffer for continued over-consumption of renewable water supplies. Despite the great scarcity of water and intensifying water shortages in this basin, a full accounting of the river’s consumptive uses and losses has never been undertaken. In this study we assemble detailed water consumption estimates from a broad array of sources to describe how surface and ground water were consumed for both direct uses (agricultural, municipal, commercial, thermoelectric power generation) and indirect uses (reservoir evaporation and riparian evapotranspiration) in each of 14 sub-basins during recent decades. We estimate that only half (48%) of water directly consumed for anthropogenic purposes is supported by renewable replenishment; the other half (52%) has been unsustainable, meaning that it is causing depletion of reservoirs, aquifers, and river flows. The over-consumption of renewable water supplies is primarily due to irrigated agriculture, which accounts for 87% of direct water consumption in the basin. At the same time, water shortages have contributed to the loss of 18% of farmland in the river’s headwaters in Colorado, 36% along the Rio Grande in New Mexico, and 49% in the Pecos River tributary in New Mexico and Texas. Farmland contraction in the US portion of the basin has resulted in lowered irrigation consumption and many cities have been able to reduce their water use as well, but irrigation in the Mexican portion of the basin has increased greatly, causing basin-wide consumption to remain high. This severe water crisis presents an opportunity for envisioning a more secure and sustainable water future for the basin, but a swift transition will be needed to avoid damaging consequences for farms, cities, and ecosystems.