ALBUQUERQUE, N.M. — Farms in the Rio Grande Valley of central New Mexico consume nearly six times as much water as the region’s cities, according to a new analysis by a team led by a University of New Mexico professor.
And bosque plants, dipping their roots into groundwater and exhaling the water through their leaves, consume nearly three times as much water as cities, according to the study.
There are uncertainties in the numbers. Other experts say the analysis may overstate farm consumption, that agriculture consumes only four times as much water as cities, not six times, and that the bosque may consume as much as five times as much water as cities, rather than three.
But that should not obscure two central issues pointedly revealed by the new analysis.
First, farms and the bosque each use a lot more water than cities, and any water policy discussion in this water-scarce region must take that reality into account. Second, the uncertainty in the numbers should be troubling. The fact that we don’t have a clearer picture of our consumption of this scarce and important resource is a problem.
The numbers come from UNM engineering professor Bruce Thomson, former head of the university’s Water Resources Program. Working with a team of experts, Thomson built a “water budget” for the valley – how much water flows into the valley in the Rio Grande and its tributaries, how much falls on the valley as rain, and what the best available data say about how it is used.
The exercise, the first attempt at building a valley water budget in a decade, was done under the auspices of the Middle Rio Grande Water Assembly, a local nonprofit group. Thomson will unveil the study’s details at a public forum scheduled for Saturday.
Thomson’s effort calculates consumption – how much is actually lost to the sky through evaporation and plant use. Water returned to the river by cities via their sewage treatment plants for downstream use is not counted against cities. Farm water that soaks into the ground, recharging aquifers, is not counted against agriculture’s share.
While differing in detail, the study has a basic message consistent with previous efforts in 1999 and 2004 – farms and the river ecosystem itself, followed by evaporation from the river and Elephant Butte Reservoir, are far and away the biggest water users in the valley, significantly larger than city use, which is often the most noticed and most frequently talked about.
David Gensler, the hydrologist for the Middle Rio Grande Conservancy District, the valley’s primary farm water agency, thinks Thomson’s numbers overestimate farm water use. Thomson acknowledges the uncertainty in the numbers, saying the purpose of his study was to provide a foundation for a discussion, not a definitive answer.
But even if Gensler is right, farms still use far more than cities – four times as much by Gensler’s calculation, instead of Thomson’s six. Either way, the water policy discussion that needs to follow is largely the same.
The farm-city split should not be surprising. This was farm country before cities grew up in their midst, and state water law (and a sense of fairness) says the people who were here first are entitled to use of the water to do the things they’ve always done with it – in this case, to grow crops.
Numbers vary, but the latest figures from the Middle Rio Grande Conservancy District and the U.S. Department of Agriculture’s Census of Agriculture suggest there is roughly 60,000 farmed acres in the river valley stretching from Sandoval to Socorro counties.
In more rural areas, especially in Valencia and Socorro counties, the impact of the agricultural economy is substantial. According to the Census of Agriculture, total farm sales in Socorro County in 2012 totaled $77 million. In Valencia County, they totaled $56 million.
“It’s historic,” Thomson said in an interview. “It’s cultural. They’ve got the water rights. Who’s going to shut them off? You can’t.”
It also benefits city folk. All that farm water spread in the network of irrigation ditches across the valley floor, along with the water sucked up by bosque trees, is a key part of what makes this such a beautiful place to live. “Everyone wants there to be a green valley,” Thomson said.
But with population growing and climate change projected to reduce the amount of water available in coming decades, something has to give.
It is easy to look at the numbers and suggest a solution. One easy one: Cities have to stop growing, or maybe even go away. They make no sense in this desert environment. Another easy one: Farming makes no sense here.
But the problem is that neither of the obvious or simplistic solutions above has even a remote chance of coming to fruition. And, no one is in charge of the decisions. As Thomson put it, there are no knobs to turn to dial down city water use or dial down farm water use. Instead, the solutions have to arise through community conversations. What kind of community do we want, and how do we figure out how to share the water to get there?
That is the focus of Saturday’s Middle Rio Grande Water Assembly discussion, “Our Water Imbalance – Creating Adaptive Strategies Together,” according to Elaine Hebbard, one of the conference’s organizers.