1Sustainable Waters, Crozet, VA, USA. 2University of Virginia, Charlottesville, VA, USA. 3Water Asset Management, San Francisco, CA, USA. 4USDA
Forest Service, Southern Research Station, Otto, NC, USA. 5Department of Geography and Spatial Sciences, University of Delaware, Newark, DE, USA.
6Department of Plant and Soil Sciences, University of Delaware, Newark, DE, USA. 7Data Science Institute, Columbia University, New York, NY, USA.
8Darden School of Business, University of Virginia, Charlottesville, VA, USA. 9Twente Water Center, University of Twente, Enschede, The Netherlands.
10Institute of Water Policy, Lee Kuan Yew School of Public Policy, National University of Singapore, Singapore, Singapore. 11Institute of Urban Development,
Nanjing Audit University, Nanjing, Jiangsu, China. 12Civil Engineering Department, Kansas State University, Manhattan, KS, USA. 13Department of
Environmental Science, Baylor University, Waco, TX, USA. 14Robert B. Daugherty Water for Food Global Institute, University of Nebraska, Lincoln, NE, USA.
15Northern Arizona University, Flagstaff, AZ, USA. 16Lehigh University, Bethlehem, PA, USA. 17University of Victoria, Victoria, British Columbia, Canada.
Water shortages have afflicted human societies for thou-
sands of years1. As population centres grow and farmlands
expand, freshwater consumption typically increases until
renewable water supplies are fully utilized (for example, in Fig. 1);
at this point, water users and freshwater ecosystems become highly
vulnerable to water shortages during drier periods2. Historically,
water shortages had local causes and consequences, involving only
the communities that were directly dependent on an overused river
or aquifer. Today, however, with trade networks encircling the globe,
demand for asparagus in the United Kingdom can contribute to the
depletion of an aquifer in the Peruvian desert3,4 and water shortages
in the Central Valley of California can affect the availability and price
of almonds and pistachios imported into the European Union5.
Climate change exacerbates water shortages by affecting both
water supplies and water demands. Higher temperatures increase
evapotranspiration, reducing aquifer recharge and watershed run-
off6. For example, Udall and Overpeck attributed one-third of recent
declines in Colorado River flows (19% below average during 2000–
2014) to temperature increases7. The Intergovernmental Panel on
Climate Change expressed high confidence that irrigation—the
largest water-using sector globally—will increase in coming decades
due to increased evapotranspiration6.
Human-induced depletion of river flows has deleteriously
affected freshwater species and ecosystems across the globe8,9 and
is a leading cause of fish imperilment in the US10–12. Richter etal.12
documented that 62% of sub-watersheds in the western US contain
at least one species endangered by flow depletion, with a total of 367
plant and animal species affected, including two-thirds of all native
fish species in the Colorado River basin. To protect species listed
under the US Endangered Species Act, water regulators have been
forced to curtail water use for irrigation in some watersheds, lead-
ing to severe political controversy and economic hardship13,14. The
annual cost of recovering Endangered Species Act-listed fish species
(more than US$800 million per year) now exceeds expenditures for
all other animal and plant groups combined15.
Water shortages have increased in both frequency and geographic
extent in the US and globally16,17. However, some recent water short-
ages have begun to stimulate policy responses. A severe drought in
California during 2012–2016 led to record levels of river and aquifer
depletion across the state and US$2.7 billion in agricultural losses in
2015 alone, provoking mandatory state-wide water use reductions
and legislation requiring preparation of sustainable groundwater-
management plans18,19. In recent decades, water extractions from
the Colorado River have exceeded total river flow, causing rapid
depletion of water-storage reservoirs (Fig. 1). In response, state and
federal water agencies are preparing demand-management plans to
stabilize reservoir levels and avoid mandatory reductions in water
deliveries to states sharing the basin’s water20–22.
For water-management plans and policies to succeed, they need
sufficiently detailed and accurate information that can enrich under-
standing of the causes of water shortages and help guide decision
making around potential solutions. Here we assess river flow deple-
tion across the US, identify direct and indirect drivers of this deple-
tion, and assess options to reduce vulnerability to water shortages.
Our findings led to closer examination of the water use and eco-
logical impacts associated with irrigation of cattle-feed crops. We
Water scarcity and fish imperilment driven by
Brian D. Richter 1,2 ✉ , Dominique Bartak3, Peter Caldwell4, Kyle Frankel Davis 5,6,7,
Peter Debaere8, Arjen Y. Hoekstra 9,10, Tianshu Li 11, Landon Marston 12, Ryan McManamay 13,
Mesfin M. Mekonnen 14, Benjamin L. Ruddell15, Richard R. Rushforth15 and Tara J. Troy 16,17
Human consumption of freshwater is now approaching or surpassing the rate at which water sources are being naturally replen-
ished in many regions, creating water shortage risks for people and ecosystems. Here we assess the impact of human water
uses and their connection to water scarcity and ecological damage across the United States, identify primary causes of river
dewatering and explore ways to ameliorate them. We find irrigation of cattle-feed crops to be 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. We assess opportunities for alleviating water scarcity by reducing cattle-feed production, finding
that temporary, rotational fallowing of irrigated feed crops can markedly reduce water shortage risks and improve ecological
sustainability. Long-term water security and river ecosystem health will ultimately require Americans to consume less beef that
depends on irrigated feed crops.
NATURE SUSTAINABILITY | VOL 3 | APRIL 2020 | 319–328 | www.nature.com/natsustain 319