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Immigration and border security will be the likely focus of U.S.-Mexico relations under the new Trump administration. But there also is a growing water crisis along the U.S.–Mexico border that affects tens of millions of people on both sides, and it can only be managed .

Climate change is in the southwestern U.S. Higher air temperatures are increasing evaporation rates from rivers and streams and intensifying drought. Mexico is also experiencing .

Growing water use is already overtaxing limited supplies from nearly all of the region's cross-border rivers, streams and aquifers. Many of these sources are contaminated with , further reducing the usability of available water.

As Texas-based scholars who study and of water policy, we know that communities, farms and businesses in both countries rely on these scarce water supplies. In our view, water conditions on the border have changed so much that the current legal framework for managing them is inadequate.

Unless both nations recognize this fact, we believe that water problems in the region are likely to worsen, and supplies may never recover to levels seen as recently as the 1950s. Although the U.S. and Mexico have moved to address these concerns by the , these steps are not long-term solutions.

Growing demand, shrinking supply

The U.S.-Mexico border region is mostly arid, with water coming from a few rivers and an unknown amount of groundwater. The main rivers that cross the border are the Colorado and the Rio Grande—two of .

The Colorado River provides water to , including seven U.S. and two Mexican states, 29 Indian tribes and 5.5 million acres of farmland. Only reaches Mexico. The river once emptied into the Gulf of California, but now so much water is withdrawn along its course that since the 1960s it typically .

The Rio Grande supplies water to , including 22 Indian tribes, three U.S. and four Mexican states and 2.8 million irrigated acres. It forms the 1,250-mile (2,000-kilometer) Texas-Mexico border, winding from El Paso in the west to the Gulf of Mexico in the east.

Other rivers that cross the border include the Tijuana, San Pedro, Santa Cruz, New and Gila. These are all significantly smaller and have less economic impact than the Colorado and the Rio Grande.

—underground rock formations that contain water—also traverse the border. With a few exceptions, very little information on these shared resources exists. One thing that is known is that many of them are .

Nonetheless, reliance on aquifers is growing as surface water supplies dwindle. Some 80% of groundwater used in the border region . The rest is used by farmers and industries, such as .

Over 10 million people in 30 cities and communities throughout the border region for domestic use. Many communities, including Ciudad Juarez; the sister cities of Nogales in both Arizona and Sonora; and the sister cities of Columbus in New Mexico and Puerto Palomas in Chihuahua, .

A booming region

About 30 million people live on both sides. Over the next 30 years, that figure is .

Municipal and industrial water use throughout the region is also expected to increase. In Texas' lower Rio Grande Valley, .

At the same time, , scientists project that snowmelt will decrease and evaporation rates will increase. The —the portion of its volume that comes from groundwater, rather than from rain and snow— in the next 30 years.

Precipitation patterns across the region are projected to be . This trend will fuel more extreme weather events, such as droughts and floods, which could cause widespread harm to crops, industrial activity, human health and the environment.

Further stress comes from growth and development. by pollutants from agricultural, municipal and industrial sources. Cities on both sides of the border, especially on the Mexican side, have a long history of into the Rio Grande. Of the 55 water treatment plants located along the border, 80% reported as of 2019.

Drought across the border region is already stoking domestic and bilateral tensions. Competing water users are , and the U.S. and Mexico are straining to for sharing water.

Cross-border water politics

Mexico and the United States manage water allocations in the border region mainly under two treaties: a 1906 agreement focused on the and a 1944 treaty covering the .

Under the 1906 treaty, the U.S. is obligated to deliver 60,000 acre-feet of water to Mexico where the Rio Grande reaches the border. This target may be reduced during droughts, which have . An acre-foot is enough water to flood an acre of land 1 foot deep—about 325,000 gallons (1.2 million liters).

Allocations under the 1944 treaty are more complicated. The U.S. is required to deliver 1.5 million acre-feet of Colorado River water to Mexico at the border—but as with the 1906 treaty, reductions are allowed in cases of extraordinary drought.

Until the mid-2010s, the U.S. met its full obligation each year. Since then, however, regional drought and climate change have severely reduced the Colorado River's flow, requiring substantial allocation reductions for both the U.S. and Mexico.

In 2025, states in the U.S. section of the lower Colorado River basin will see a reduction of from prior years. Mexico's allocation under the 1944 treaty.

This agreement provides each nation with designated fractions of flows from the Lower Rio Grande and specific tributaries. Regardless of water availability or climatic conditions, Mexico also is required to deliver to the U.S. a minimum of 1,750,000 acre-feet of water from six named tributaries, averaged over five-year cycles. If Mexico falls short in one cycle, it can make up the deficit in the next five-year cycle, but cannot delay repayment further.

Since the 1990s, extraordinary droughts have caused Mexico . Although Mexico repaid its water debts in subsequent cycles, these shortfalls raised diplomatic tensions that led to and large-scale water transfers from Mexico to the U.S.

Mexican farmers in Lower Rio Grande irrigation districts who had to shoulder these cuts felt betrayed. In 2020, they protested, confronting federal soldiers and .

U.S. President Donald Trump and Mexican President Claudia Scheinbaum clearly appreciate the political and economic importance of the border region. But if water scarcity worsens, it could supplant other border priorities.

In our view, the best way to prevent this would be for the two countries to recognize that conditions are deteriorating and so that it reflects today's new water realities.

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