Changes are needed in 80-year-old water treaty to accommodate the drying climate.

Water levels at Amistad Reservoir, one of the main water storage reservoirs for the Rio Grande along the U.S.-Mexico border, fell to record lows in February 2024. Photo courtesy of Alex Demas/USGS

By Brett Walton, Circle of Blue – March 19, 2024

Reservoirs sink to record lows. Farmers lament shortage of water for irrigation. Senior officials, buffeted by partisan disruption, haggle over the terms of new management plans.

These scenes define life along the Rio Grande, a major river the United States shares with Mexico that is withering in a hotter climate. By most measures, the iconic waterway is in serious trouble.

Relentless warming from the buildup of greenhouse gases in the atmosphere is sapping the 1,900-mile river, from its headwaters in Colorado’s San Luis Valley all the way to the Gulf of Mexico. Unregulated groundwater extraction in both countries adds to the basin’s water stress, so much so that Texas has taken New Mexico to the U.S. Supreme Court over the matter.

To the south, conditions are no better. Mexico is required by name treaty here to deliver an average of 350,000 acre-feet to the U.S. from Rio Grande tributaries every five years. The current cycle ends in 2025. Once again, Mexico is behind. It’s roughly 1 million acre-foot deficit puts it farther behind at this point in the cycle than ever before.

That could mean big trouble, and not just for the river. The last time Mexico was delinquent, in September 2020, two people died in Chihuahua, a state in northern Mexico, when the Mexican National Guard fired at farmers protesting water releases from La Boquilla dam that were meant to satisfy the country’s downstream water delivery obligation.

At the center of the controversy is the 80-year-old treaty that governs water supplies from the Rio Grande and two more border rivers — the mighty Colorado, which drains much of the Southwest, and the tiny Tijuana River in northwestern Mexico. Like many octogenarians, the treaty is showing its age, struggling to adapt to the realities of a hotter era in the arid Southwest.

U.S. and Mexican negotiators have worked out a deal for small adjustments to how the treaty is implemented. The U.S. is ready to sign, according to Maria-Elena Giner, commissioner of the International Boundary and Water Commission (IBWC), the binational organization that oversees the 1944 treaty. But Mexico, she says, is still consulting with state governments before granting its approval.

The changes are necessary, says Stephen Mumme, a scholar who closely follows the workings of the IBWC. But they will likely fall short of the substantial regulatory, administrative, and technical overhaul that is required for the river and its users to have a sustainable future as the basin dries and its population and industry grows.

“These trends in the basin are going to make it very, very difficult for Mexico to be meeting its formal obligation to the U.S. in quite the same way that it has in the past,” Mumme says.

The Rio Grande flows through Big Bend Ranch State Park. Photo courtesy of Flickr/Creative Commons user CMy23

The emblems of the current crisis are Amistad and Falcon reservoirs, twin water storage facilities downstream of Big Bend National Park on the river’s main stem. They are the Mead and Powell of the lower Rio Grande – sentinel reservoirs that indicate, with a glance, the vigor of the river system.

A quick check reveals ill health. Amistad set a record low last month. Falcon, the smaller reservoir, is only 15 percent full. The Texas Commission on Environmental Quality reckons that only 22 percent of irrigation demands from the river can be met this year.

Though the river’s severe water depletion is plainly evident, Rio Grande negotiations are complicated by border politics, which is heavily contested terrain. Migrants crossing from Mexico are arriving in the U.S. in record numbers, thrusting immigration to the center of state and national debate. To counter the migrant surge, Texas Gov. Greg Abbott launched Operation Lone Star, seizing land on the banks of the Rio Grande and dispatching patrol units from the state police and Texas National Guard.

Elected officials play to their constituencies. When Mexico falls behind in its deliveries, Texas politicians are quick to complain. “The Mexican government bears a responsibility to honor the terms of this treaty,” Rep. Monica De La Cruz, whose district abuts the Rio Grande, said in the House of Representatives last September. “American farmers and ranchers should not bear the burden of Mexico’s failure to uphold its end of the bargain.”

But water negotiators are trying to set the partisan rancor aside, according to Gabriel Eckstein, a Texas A&M University law professor. The International Boundary Water Commission is helping. Together with its Mexican counterpart CILA it implements the treaty through a series of negotiated agreements called “minutes,” a process that, by design, is incremental.

Minutes are a clever work-around, Eckstein says. In a legal sense, they are not amendments, which need to be ratified by national legislatures. But they achieve the same ends: updating the treaty to new conditions. “It’s extremely flexible and effective,” he says. “It’s one of those things that, why didn’t we do this on every treaty?”

Minute 325, the most recent declaration related to the Rio Grande, was signed in October 2020 in response to Mexico’s late payment in the last five-year cycle. That minute used some creative accounting – Mexico shifted water it already had in storage in Amistad and Falcon to the U.S. – to resolve the crisis.

Giner, the IBWC commissioner, said the new minute under negotiation would build on Minute 325. It would ratify existing hydrology and policy working groups while adding new groups on environment and infrastructure, which would discuss ways to stretch and expand supplies through conservation and wastewater recycling. More importantly, it would enshrine new accounting tools to incentivize Mexico not to delay its deliveries. CILA representatives did not respond to requests for comment.

Future minutes could be even more difficult to negotiate. Mumme and other observers point out three glaring omissions in the 1944 treaty that ought to be corrected.

One is a failure to account for climate change. Understandable when the document was ratified, but increasingly an untenable position today for water availability.

“The assumptions that were around in 1944 about how much water the basin would be able to supply haven’t turned out to be true,” Giner says.

A second challenge is the schedule for water deliveries. Mexico is supposed to send an average of 350,000 acre-feet a year from six tributaries. The deliveries, however, are measured across a five-year cycle. And if Amistad and Falcon are filled, at any point, the cycle resets.

This accounting method inspires procrastination, Mumme says. He jokes, with some truth, that “it’s a system that encourages Mexico to pray for a hurricane.” A week of drenching rains late in Year Five could bail out four years of dawdling on deliveries.

The third major omission is groundwater. It is not mentioned in the 1944 treaty, says Rosario Sanchez of the Texas Water Resources Institute. She calls the failure to correct this mistake “a ticking bomb” as the river declines and more people and industries turn on their pumps to cover the surface water shortfall.

Groundwater shared by the two countries, by and large, is a mystery, according to Sanchez, who is one of the few researchers studying groundwater in the border region. “It is not accounted for, it’s not monitored, it’s not quantified,” she says.

If a creek is dry, groundwater might seem like an easy tradeoff. It’s not. Groundwater moves beneath the surface, eventually flowing into arroyos and rivers, sustaining these waterways during dry periods. Pumping groundwater, in many cases, steals water from the river.

From the few available monitoring reports, Sanchez has put together rudimentary maps of border aquifers, not just in the Rio Grande region but across the international boundary. Half show a deficit, she says. In general, these water sources are a black box. “We just don’t know how much water has been extracted.”

At this point, the Rio Grande needs all the water it can get. Mumme thinks that the treaty will eventually be adjusted so that each side takes a cut during times of extreme deficit. An agreement to share shortages between the U.S. and Mexico already exists on the Colorado River. A main obstacle on the Rio Grande, Mumme says, are Texas representatives, who want all that the treaty grants them.

A treaty that mandates fixed volumes of water is fine – as long as that water is available. It falters, Sanchez says, when those fixed volumes exceed what nature provides.

“Even if Mexico wants to comply with the treaty, where is the water going to come from?” she asks. That is a question future negotiators must answer.