Across the globe, humans are using freshwater resources faster than those resources can be naturally replenished. In the Western United States, for example, water extractions from the Colorado River have exceeded total river flow, causing rapid depletion of water storage reservoirs. In addition, as these water sources dry up, species of fish, plants and animals are also adversely impacted.
A new study published in Nature Sustainability shows that irrigation of cattle feed crops is the greatest consumer of river water in the Western United States, implicating beef and dairy consumption as the leading driver of water shortages and fish imperilment in the region.
Kyle Davis, assistant professor of Geography and Spatial Sciences and Plant and Soil Sciences, performed the crop water-use estimates for the study. He said the researchers wanted to understand what sectors within the U.S. economy and which crops contributed the most to unsustainable water use, as well as what regions of the United States were most vulnerable to that water loss.
"We looked at agriculture, industry, domestic use, and thermoelectric power generation and quantified what their water demand is on a monthly basis," said Davis. "Then we incorporated those estimates into a national hydrological model to understand how those human water uses within different watersheds in the United States would lead to reduced availability for people and aquatic species downstream."
Irrigation of cattle feed crops is the single largest consumptive user at both regional and national scales, accounting for 23 percent of all water consumption nationally, 32 percent in the Western U.S. and 55 percent in the Colorado River basin.
Alfalfa, for example, is a water-intensive crop that is planted on a large scale to support the beef industry in the Western U.S. In addition, a crop like corn, which on its own is pretty water use efficient, is produced on such a large scale to support the cattle industry that it ends up requiring a lot of unsustainable water use.
After identifying crops and sectors that were contributing to unsustainable water use, the researchers estimated the implications for aquatic species in the Western U.S.
"We made estimates of how many different types of fish species we would expect to have local or global extinctions as a result of this increased water use to support feed production for beef," said Davis.
Sixty fish species in the Western U.S. are at an elevated risk of global extinction due to flow depletion, and 53 of those are primarily due to irrigation of cattle-feed crops.
Summer water flow depletion in particular is responsible for nearly 1,000 instances of increased risk of local extinction of fish species in watersheds in the Western U.S. Of these 1,000 instances, 690 are estimated to have occurred primarily due to irrigation of cattle-feed crops, absent any other water uses.
As far as solutions to the problem go, the research points to fallowing programs, specifically ones that are practiced in a couple of irrigation districts in California.
"The idea is that you pay farmers not to cultivate anything in their field for a particular growing season and the water that they would have applied for irrigation can then be repurposed for other uses," said Davis. "It can be diverted to increase urban water availability or used to increase environmental flows and the water available for natural systems. We've found that fallowing programs are really effective in terms of saving water or effectively repurposing it."
Davis also said that the intent of the study is not to vilify farmers or ranchers, as they are at the heart of the solution to the water challenges.
"We see huge opportunities for farmers and ranchers to be appropriately compensated for helping resolve our water problems and thereby enhancing their incomes and benefiting their communities," said Davis.
The paper also showed how different regions in the U.S are reliant on western beef production to meet their demand. They did this to show that production - and the water resources to support it - often occurs in places geographically removed from where beef is actually consumed, meaning dietary decisions can impact places that are geographically removed from where those foods are actually produced.
In Delaware, consumers are contributing little to water scarcity in the West, as most of the beef in the eastern United States is not sourced from the western states. Beef consumers living in the Los Angeles, Portland, Denver and San Francisco areas, however, consume beef that relies on water resources in places where hydrological and ecological impacts are high.
"Consumers can be made more aware that by eating a lot of beef, they're potentially contributing to unsustainable water use in certain parts of the U.S. More importantly though, this information could be used by corporations and others with control over food supply chains to source beef and cattle feed from places where water is more abundant," said Davis.
Overall, Davis said that he doesn't want to give the impression that all beef is bad, noting that in many places, cattle are important for converting grasses that humans can't eat directly into edible material.
"Cattle play an important role in food security and nutrition, but their environmental impacts can be large. Ensuring that beef and cattle feed are produced in places where water resources are relatively abundant can help to achieve balance between satisfying our diets and protecting the environment," said Davis. "In all, it's good to have knowledge of where your food comes from and what natural resources it requires in order for each person to make more informed food choices."
This study was a multi-institutional effort between researchers at a variety of universities, government agencies, and non-governmental organizations. The lead author on the paper is Brian Richter, president of Sustainable Waters, a global water education organization, and research support for the study was provided by the FEWSION project founded in 2016 by a grant from the Innovations at the Nexus of Food, Energy and Water Systems (INFEWS) program which is sponsored by the National Science Foundation and the United States Department of Agriculture.