The United States and Mexico are tussling over their dwindling shared water supplies after years of unprecedented heat and insufficient rainfall.
Sustained drought on the middle-lower Rio Grande since the mid-1990s means less Mexican water flows to the U.S. The Colorado River Basin, which supplies seven U.S. states and two Mexican states, is also at record low levels.
A 1944 treaty between the U.S. and Mexico governs water relations between the two neighbors. The International Boundary and Water Commission it established to manage the 450,000-square-mile Colorado and Rio Grande basins has done so adroitly, according to our research.
That able management kept U.S.-Mexico water relations mostly conflict-free. But it masked some well-known underlying stresses: a population boom on both sides of the U.S.-Mexico border, climate change and aging waterworks.
1944 to 2021
The mostly semiarid U.S.-Mexico border region receives less than 18 inches of annual rainfall, with large areas getting under 12 inches. That’s less than half the average annual rainfall in the U.S., which is mainly temperate.
The 1940s, however, were a time of unusual water abundance on the treaty rivers. When American and Mexican engineers drafted the 1944 water treaty, they did not foresee today’s prolonged megadrought.
Nor did they anticipate the region’s rapid growth. Since 1940 the population of the 10 largest pairs of cities that straddle the U.S.-Mexico border has mushroomed nearly twentyfold, from 560,000 people to some 10 million today.
This growth is powered by a booming, water-dependent manufacturing industry in Mexico that exports products to U.S. markets. Irrigated agriculture, ranching and mining compete with growing cities and expanding industry for scarce water.
Today, there’s simply not enough of it to meet demand in the border areas governed by the 1944 treaty.
Three times since 1992 Mexico has fallen short of its five-year commitment to send 1.75 million acre-feet of water across the border to the U.S. Each acre-foot can supply a U.S. family of four for one year.