Many eyes on the Colorado River. The Rio Grande may be more urgent.

New study of river from headwaters in Colorado to the Gulf of Mexico demonstrates need for changes.

by Allen Best

In November 2023, I stopped by the office of Cleave Simpson, then (and still now, at least for a brief time more), the general manager of the Rio Grande Water Conservancy District.

There, in Alamosa, he shared with me his observation that the Rio Grande during the 21st century has had water declines parallel to those of the Colorado River.

Both rivers originate in Colorado, and neither river has been able to deliver the water assumed by any number of diversion projects. Problems began in the 20th century but have intensified greatly in the 21st century because of drought but also rising temperatures.

The Rio Grande has had 17% reduced flows since 2000. The Colorado River flows have declined 20%.

Of the two rivers, the Rio Grande is longer, at 1,900 miles but carries less water, 9.1 million acre-feet/year. The Colorado flows 1,450 miles and has been carrying an average 15.4 million acre-feet. Neither river has delivered water into oceans with any reliability in decades.

Sandhill cranes and a few mallard ducks roost at sunset on a sandbar of the Rio Grande in Albuquerque during January. Photo(and copyright)/WWF-us, Diana Cervantes. Top: The San Luis Valley near Del Norte. Photo/Brian Richter

Despite these parallels, the Colorado has received far more attention, as is pointed out in a new report by Brian Richter of the World Wildlife Fund and nine others from academic institutions in Arizona, California, and other states.

Why is that? The Colorado provides drinking water for about 40 million people compared to 15 million for the Rio Grande. In irrigated agriculture, it’s a similar story: 22,300 square kilometers in the Colorado River Basin vs. 7,800 square kilometers in the Rio Grande.

“However, the water crisis facing the Rio Grande Basin is arguably more severe and urgent than the Colorado River Basin,” Richter and his colleagues contend. They argue for some rethinking and institutional alignments to help ratchet water use down to sustainable levels.

The study is the first full accounting of how water is consumed across the entire Rio Grande Basin. Mexico calls it the Rio Bravo.

Doesn’t Colorado also have a strong accounting system, as necessary to meet requirements of the 1938 compact among states that share the Rio Grande?

Yes, says Richter. However, he adds a “but.” He reports difficulty in getting estimates of how much water is being consumed by each sector and by each crop. He believes he has succeeded.

“To my knowledge, nobody has laid out the numbers at the level of clarity and accuracy that we were able to accomplish,” he said.

Another major contribution of the paper is the estimation of the degree to which water consumption is unsustainable, he said.

“We estimate that 11% of water consumption in Colorado is unsustainable. Natural replenishment from snowmelt runoff, precipitation, and groundwater recharge supplies only 89% of the water being consumed; the remainder (deficit) is being met by depleting groundwater.”

“The Rio Grande basin is at a tipping point, and everyone needs to be part of the solution,” said Enrique Prunes, a co-author and the World Wildlife Fund Rio Grande manager. “These findings will help us rethink how we manage water to secure a future for everyone.”

For the second time in the 21st century, this segment of the Rio Grande in Albuquerque went dry, leaving this image of cracked sediment on a blistering afternoon on Aug. 7, 2025. Photo(and copyright)/WWF-us, Diana Cervantes

Dry cracked sediment from the Rio Grande on a blistering afternoon on Aug. 7, 2025 in Albuquerque, N.M. For the second time in the 21st century the Rio Grande has gone dry in the Albuquerque stretch. (TC) (EDITOR’S NOTE:
T/C, to fact check).

Agriculture uses 99.9% of the water in Colorado’s San Luis Valley and 87% in the basin altogether.

Dramatic declines in reservoir storage illustrate the scope of problem. Altogether, 12% of reservoir storage has been lost in the 21st century. The decline is most severe in New Mexico, where 71% less water was stored at the end of 2024 compared to 2002.

Groundwater depletion has been even more drastic. Roughly 15 times more groundwater has declined compared to surface storage. The two are coupled. As surface water supplies decline, groundwater mining grows.

Draining of aquifers has been a particularly vexing problem, as was explained in a story published in Headwaters magazine in June (and published in installments at BigPivots.com during July). See in particular 20th century expansion and 21st century realities in the San Luis Valley

“In the San Luis Valley of Colorado, diminished river flows and aquifer recharge have led to continued over-pumping, causing aquifers levels to decline,” Richter and his team write. “The Colorado state engineer has threatened to shut off hundreds of groundwater wells if the aquifer supporting irrigated farms cannot be stabilized.”

The San Luis Valley is famous for its potatoes as well as the barley to make Coors beer, but potatoes use just 7% of the water and barley 9%. The vast majority of water in the valley produces feedstocks for livestock: 47% for alfalfa, 27% for other hay, and 6% for pasture lands.

The study finds that groundwater in the San Luis Valley has been depleted at a rate of 89,179 acre-feet/year, equivalent to 11% of the annual average of direct water consumption in the valley.

What can be done? Large cities have done more with less. Albuquerque’s population grew 40% while its water use declined by 17%. However, municipal and commercial water consumption account for only 7% of all direct consumption in the three-state and two-country basin.

Strategies for reducing consumption in irrigated agriculture have been proven but must be rapidly deployed at sufficient scale and financially sustained by governments, companies, and credit institutions to rebalance the basin’s water budgets, state, and binational levels.

At the same time, water shortages have contributed to the loss of 18% of farmland in the river’s headwaters in Colorado, 36% in New Mexico, and 49% in the Pecos River tributary in New Mexico and Texas.

Strategies being embraced to curb groundwater drafting in the closed basin of the San Luis Valley have been controversial. A key case is likely to go before the Colorado Supreme Court. In Mexico, cutbacks have led to violence. One protestor died.

The study points to several strategies that could reshape how water is used in the basins. These include restoring river habitats, adjusting dam operations to better support seasonal flows, improving water-sharing agreements, and helping farmers switch to crops that require less water.

That effort to encourage crop-switching has been underway in the San Luis Valley, but with successes only at the margins.