Study finds unsustainable water use across the Rio Grande

Across the Rio Grande–Bravo basin, which runs from Colorado to Mexico, water stress has been building for years.

Reservoirs that once relied on steady snowmelt are now noticeably lower. Aquifers that supported farming communities for generations continue to decline, dropping faster than they can recharge. In some stretches, the river, which runs nearly 3,000 kilometers, disappears into dry sand before reaching its endpoint.

Despite this growing strain, a full, basin-wide picture of how the river’s water is used and how much is being lost didn’t exist. People could see the symptoms, but the underlying patterns and specific drivers of water decline were not well understood.

That is beginning to change. Landon Marston, associate professor of civil and environmental engineering at Virginia Tech, is part of a group of researchers that have completed the first comprehensive assessment of the Rio Grande–Bravo basin, using decades of data from 14 sub-basins across the United States and Mexico. This multi-institutional effort, led by Brian Richter at Sustainable Waters, offer the clearest look yet at how limited water supplies are being allocated and where the system is breaking down.

One result stood out. More than half of the water consumed across the basin is effectively being used unsustainably, pulled from reservoirs and aquifers much faster than natural processes can replace it.

“For the first time, we can see a complete, binational view of how water is being used across the entire Rio Grande–Bravo basin,” said Marston. “This accounting is essential because it lays bare the reality of the basin’s situation. More than half of the water people are using isn’t sustainable, putting the long-term health of farms and cities at serious risk.”

What the new analysis reveals

In the basin-wide assessment, which relied on satellite observations, detailed water use records, crop models, and hydrologic modeling, the research team worked to understand every major way that water is used. This included irrigated agriculture, municipal supplies, industrial needs, power generation, even losses from reservoir evaporation and thirsty riverside ecosystems. When researchers combined all of these data sources, a clear pattern emerged.

Only about 48 percent of the water people use in the basin is naturally replenished each year. The other 52 percent is coming from reserves that are steadily running out, such as groundwater that drops a little lower each season, reservoirs sitting at historic lows, and river stretches that no longer carry enough flow to stay connected.

The reservoirs tell the story plainly. By late 2024, New Mexico’s largest reservoirs were only 13 percent full, meaning just one or two very dry years could push them to empty.

A river running on empty

The Rio Grande–Bravo has never been a high-flow river, even though it covers a huge distance. But the factors behind today’s water shortages started long ago. As early as the late 1800s, heavy irrigation in Colorado’s San Luis Valley was already reducing the amount of water moving downstream. By the 1950s, some sections, now known as the “Forgotten Reach,” were drying up completely, well before climate models were part of public planning.

Today, the pressures are even greater. Only about 15 percent of the river’s natural flow makes it to the lower basin near the Gulf of Mexico. A prolonged, two-decade megadrought has cut snowmelt by 17 percent since 2000, and scientists no longer view it as a short-term dry spell but as a shift toward a more arid climate. Looking ahead, projections show the river could lose an additional 16 to 28 percent of its flow in the coming decades.

“Nature is providing less water,” said Marston, “and human demand continues to grow.”

A narrow window for transformation

If the basin continues on its current path, the challenges will only grow, according to the study. More farmland could be lost, aquifers could collapse further, and cities could face even greater water stress. Traditional solutions, such as desalinating water or importing it from elsewhere, are unlikely to be realistic for the farmers and communities who rely on local supplies.

The study points to several possible paths forward, all related to agricultural water use.

Agriculture uses nearly 90 percent of the water in the basin, so changing what and how crops are grown will be critical. Farmers might switch to crops that need little or no irrigation, or they could adopt deficit irrigation practices, carefully reducing watering while still producing viable harvests. In the most water-stressed areas, some farmland may need to be repurposed entirely for habitat restoration, solar farms, or other uses that require far less water.

Reimagining the future

Even in a basin shaped by scarcity, the current water crisis offers an opportunity to imagine a more sustainable future, Marston said. Across other water-stressed communities in the western United States, programs and scenario-planning efforts are helping residents rethink how to manage land and water more wisely. The Rio Grande–Bravo could follow a similar path, using these lessons to guide decisions and explore new possibilities, he said.

This comprehensive accounting does more than show how far the basin has fallen out of balance, Marston said. It highlights where change is possible and where it is urgent.