Reviving the Rio

The Rio Grande near the Colorado-New Mexico state line. Photo by Brian Richter

“There are few river systems in the world that have experienced such massive transformation so rapidly: in just 50 years, from the 1880s to the 1930s, the Rio Grande was converted from a largely natural, free-flowing river into a heavily depleted and laterally constrained channel fully harnessed for farm irrigation. That makeover has largely persisted throughout the last century.” 

And so begins the story we tell in our latest journal paper, “Opportunities for Restoring Environmental Flows in the Rio Grande–Rio Bravo Basin Spanning the US–Mexico Border.” It’s a hopeful tale, though, because even while the Rio remains severely depleted, farmers and conservationists are aligning in a search for solutions that can improve water security for farms and river ecosystems.

The Taming of the Rio

I’ve always been amazed at the determination, perseverance, and aspirations of past generations to get massive construction projects built, especially when those people lacked mechanized equipment such as bulldozers and backhoes. Anglo settlers began arriving in the San Luis Valley of southern Colorado in the 1870s, and by the early 1890s had built giant irrigation canals with enough capacity to divert every single drop of the snowmelt runoff rushing off the San Juan and Sangre de Cristo mountains each spring.

Still today, those canals continue to capture most of the river’s flow and route it onto farm fields, allowing only a small fraction to run downstream into New Mexico. In some years only one-fifth of the river’s water escapes the gauntlet of irrigation canals in the San Luis Valley. In some months, such as during the spring snowmelt pulse in May 2013, less than 5% of the river’s flow passed downstream into New Mexico.

This figure from the paper illustrates the drastic change in river flows at Lobato, Colorado, driven primarily by large-volume farm diversions in Colorado. The red line and shading indicate flows measured during 1975-2020, the blue line and shading indicates what ‘natural’ (undepleted) flows would have been.

New Challenges with Climate Warming

Thanks to an important interstate water-sharing agreement passed in 1938 (the Rio Grande Compact), Colorado must leave some portion of the river to flow downstream into New Mexico, and in turn, New Mexico must do the same for Texas.

New Mexico has for decades used its share of the Rio prosperously, enabling cities such as Albuquerque to grow and farmers to produce the state’s iconic chile peppers and protein-rich alfalfa for dairies. However, climate warming is already taking a heavy toll on river flows: since 2000, the river’s flow has been 16% lower than in the 20^th century. Worse yet, because the Rio Grande Compact’s water-sharing requirements vary according to the volume of runoff each year — requiring proportionately less water sharing during drier years — New Mexico has been receiving 40% less water in recent decades.

This dire situation has set up both a crisis and an opportunity. The crisis is three-fold: (1) there’s not enough water to sustain farm irrigation at pre-2000 levels; (2) New Mexico has fallen behind in its required deliveries of water to Texas, resulting in a lawsuit now before the US Supreme Court; and (3) the drying river has put greater stress on highly endangered species such as the Rio Grande silvery minnow and threatens the extensive cottonwood bosque (forest) lining the river’s course.

The opportunity is for farmers and conservationists to work together to resolve their mutual problem.

Seeking Solutions

In our new paper we explored some possible ways to bring water use back into a sustainable balance with the Rio’s climate-diminished river flows within New Mexico.

Importantly, we began by quantifying how much water is needed to support river ecosystems based on an environmental flow assessment. A coalition of conservation entities are presently discussing the full range of hydrologic conditions needed to support the species and ecosystems sustained by the river’s flow regime, and their recommendations should be available by June 2024. But for this pilot analysis, we looked only at the summer low flows that are most affected by irrigation diversions, focusing on the river segment from Albuquerque to San Marcial. Based on previous scientific studies we determined that the river needed an average flow of 350 cubic feet per second (10 cubic meters per second) during April-September at Albuquerque. Recent summer flows have averaged only 270 cfs (7.7 m³/s), leaving a ‘gap’ of 17,000 acre-feet (21 million cubic meters) during April-September.

Using detailed crop maps and mathematical formulas to estimate crop water needs, as well as optimization techniques and agricultural data on farmer profits, we were able to explore different arrangements of the crop mosaic that could sustain farmer profits while saving enough water to close the environmental flow gap. In this experimental pilot, we found that by increasing chile pepper production from 2% to 12% of the crop mosaic we can achieve the targeted level of water savings while also sustaining farmer profits (chile peppers yield 20 times more profit than alfalfa while using much less water). But this outcome would also necessitate transforming 18% of existing croplands into other uses, such as restored wildlife habitat.

We emphasize in our paper that our pilot analysis is for illustrative purposes only. Real solutions must be developed in close collaboration with farming communities, such that any changes in farm practices or crops grown can be done in a way that is preferred by farmers and achieves the financial results and food production they are seeking. But our initial results give us hope: there appear to be workable strategies that can secure the future of agriculture at a sustainable level of production while allowing more water to flow through the river system to benefit both the river ecosystem and satisfy Compact requirements.

We conclude our paper by pointing out that none of these desirable outcomes will likely be achieved without the ability to financially incentivize and reward farmers for driving these solutions. Thankfully, this great need has recently gained the support of US Senators from both Colorado and New Mexico, who joined together in a letter to Interior Secretary Deb Haaland that advocates for federal funding support for climate adaptation efforts in the Rio Grande.

The Rio Grande is at a critical breaking point that could change the landscape dramatically. Species lost to extinction are gone forever. When farmers go out of business because of water shortages, their farmlands are rarely recovered; already, 45% of farmlands along the Rio Grande in New Mexico have gone out of production since 2000. We need to foster adaptive changes in these agricultural landscapes at a pace fast enough to catch up with — and get ahead of — climate change, or many of the environments and habitats that have shaped our livelihoods and cultures could soon disappear. We hope that our work can help illuminate some possible ways forward.