Science in Action: The Colorado River Basin Study

Sunrise on the Colorado River at Lee's Ferry, Arizona.

Sunrise on the Colorado River at Lee’s Ferry, Arizona. Photo: L. Reynolds

By Lindsay Reynolds

The Colorado River supplies water to people and ecosystems in 9 western states in the US and Mexico, including almost 5.5 million acres of irrigated lands and nearly 40 million people1. The Colorado, with headwaters in the snowy Rocky Mountains and a path through some of the most arid regions in North America, is one of the most intensively managed river systems in the world. For many years now, research scientists have been warning of impending water shortages in the basin2,3. Last week, the non-profit conservation group American Rivers named the Colorado the most endangered river in the nation. Population growth in combination with limited water and the potential effects of a changing climate are leading down a road to a very dry future.

Just before the end of 2012, the US Bureau of Reclamation released the final study report for an impressive piece of government science: The Colorado River Basin Water Supply and Demand Study (CRB Study). This study was notable for a number of reasons: its technically detailed nature, its comprehensive scope, the collaboration between Reclamation and all the basin states, and the significant public outreach that was involved. It’s a good example of how relevant science has moved from academia to informing public policy at a key moment in time.

Colorado River Basin Study Figure 3: The Study Area

Colorado River Basin Study Figure 3: The Study Area

Where academics and stacks of white papers have failed to provide a common rallying point for water managers in the Basin States, Reclamation has been able to build on existing science to deliver a much-needed call-to-arms. As manager of the two largest reservoirs on the river (Lake Powell and Lake Mead) and the second largest wholesaler of hydropower in the US, Reclamation is a powerful voice in the basin. They have necessarily taken the lead on building the broad-scale river system models to guide basin water management. The CRB Study included several major components:

  • Develop future water supply and demand scenarios
  • Estimate future water supply and demand through 2060
  • Analyze potential  future supply and demand imbalances in the river system
  • Document and analyze options to resolve supply and demand imbalances

To estimate water supply over the next 50 years, Reclamation scientists relied on a hydrologic model they have been building and testing for years, based on work by Dennis Lettenmeier and colleagues at the University of Washington2. They ran several scenarios through the hydrologic model including recent-historical, paleo-historical and GCM future climate scenarios to produce estimates of future water supply. In the second phase of the study, Reclamation scientists estimated future demand through 2060, based on several scenarios of population growth, energy use, irrigated lands and technological advancements.

Reclamation found that water supply in the basin is likely to fall by at least 9 percent over the next 50 years (current water supply averages about 14.5 million acre feet4). Shortfalls between supply and demand will range between 3 and 8 million acre feet by 2060 (current water use in the basin is about 15 million acre feet). The CRB has already had shortfalls in recent drought years which have been buffered by storage in reservoirs, but Reclamation found that more critical imbalances could happen as early as 2025.

Colorado River Basin Study Figure 12: Historical water supply and demand on the left of the dashed line, model-projected supply and demand on the right of the dashed line.

Colorado River Basin Study Figure 12: Historical water supply and demand on the left of the dashed line, model-projected supply and demand on the right of the dashed line.

What about river-dependent ecosystems and environmental flows? The river is already so over-allocated that it runs dry before it reaches its outlet to the sea. In addition to all the human demands for water along the Colorado, Reclamation attempted to quantify the needs of fish, wildlife and riparian habitats; the amount of water allocated for environmental flows varied between scenarios. The estimates of environmental flows, although informed by scientific experts, wildlife refuge managers and conservation groups, were relatively coarse and near the end of the report Reclamation acknowledges these shortcomings. However, in an effort led by The Nature Conservancy, they are actively working on improving how they model environmental flow needs in the Basin.

Given the grave outlook for water imbalances in the basin, Reclamation set out to explore as many options as possible to resolve these imbalances. They conducted a huge public outreach effort soliciting input from stakeholders in the Basin: state and city water managers, federal land managers, private land owners, tribal leaders, conservation groups and the general public. They ended up with a list of more than 150 ideas for resolving shortfalls. These options included everything from water conservation projects in cities, to agricultural water conservation such as drip irrigation, to expensive and intensive ideas such as desalination plants in southern California and building a pipeline to transport water uphill from the Missouri River to major cities in Colorado. For most of these options, they quantified costs and benefits and provided robust comparisons between options. Simple water conservation measures came out on top in terms of the inexpensive, “low-hanging fruit.”

Fortunately, Reclamation it not just dropping these results and waiting for stake-holders to act, they are also following up with meetings this year between stake-holders. Also, the comment period for the report was extended to April 19 in order to gather more input. They hope to facilitate dialogue and action towards policy changes that can lead to a more sustainable Colorado River Basin.

From a nuts-and-bolts hydrologic model, to a social science survey of water-saving options and an economic cost-benefit analysis, the CRB Study is far-reaching in its scope. It’s exciting to see this kind of multi-faceted science put to work. Although the environmental flows component is still a work-in-progress, Reclamation is interested in finding the best river science to inform their models. Hopefully water management solutions can be reached before it’s too late for the Colorado River and all the ecosystems and people that depend on it.

Bonus: a 3 minute video of footage from along the entire length of the Colorado River

1 Bureau of Reclamation Colorado River Basin Supply and Demand Final Study Report

2 Barnett TP, Pierce DW. 2009. Sustainable water deliveries from the Colorado River in a changing climate. Proceedings Of The National Academy Of Sciences Of The United States Of America 106: pp 7334–7338.

3 Christensen NS, Lettenmaier DP. 2007. A multimodel ensemble approach to assessment of climate change impacts on the hydrology and water resources of the Colorado River Basin. Hydrology And Earth System Sciences 11: pp 1417–1434.

An acre-foot equals 325,851 gallons, about enough to meet the needs of two families of four for a year.

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