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May 2014

Energy and Environment

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Adapting to a changing Colorado River ... Studying the Colorado River Basin: interview with David Groves and Jordan Fischbach

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Adapting to a Changing Colorado River

map of the Colorado River Basin

The Colorado River system is a critical resource for the southwestern United States, providing power and water for nearly 40 million people in seven states and 22 tribes. However, in part due to 14 years of drought, the River's reservoirs are being rapidly depleted, threatening curtailment in water deliveries and power production. In the River's Lower Basin, which includes California, Arizona, and Nevada, demand for water already exceeds its legal allocations, and demand in the Upper Basin states--Colorado, Utah, Wyoming, and New Mexico--is growing.

Together these demands will soon exceed available supplies even in non-drought periods. Climate change further threatens to exacerbate this imbalance.

In response to directives in the 2009 Secure Water Act, the Bureau of Reclamation and water-management agencies representing basin states undertook a study to evaluate and address these supply and demand imbalances over the coming 50 years. RAND joined the study mid-way, in January 2012, to help define the key Basin vulnerabilities and identify strategies to reduce those vulnerabilities.

The study team used a sophisticated simulation model of the Colorado River and found that the Basin is vulnerable to many plausible future conditions, particularly when considering the potential effects of climate change.

The study team then identified dozens of different options for increasing supplies or reducing demand. These options were grouped into a small number of portfolios reflecting different approaches for addressing the imbalance. Each portfolio included a subset of prioritized options that would be implemented over time as needed.

All of the portfolios were successful in reducing system vulnerability.

  • Portfolios that emphasized options with favorable environmental characteristics, such as water banking, were found to be more effective in addressing Upper Basin vulnerabilities.
  • Portfolios that included options designed to reliably increase supplies, such as seawater desalination or imports from other basins, were more effective in addressing Lower Basin vulnerabilities.
  • Costs to implement the needed options could reach between $2 billion and $7 billion a year (in 2012 dollars) by 2060, and were higher for portfolios emphasizing supply reliability.

One of the most important lessons gleaned from the study was that a number of different options are needed now, regardless of the strategy chosen or plausible future conditions.

  • In more than 90 percent of all futures considered, increases in municipal and industrial water conservation are needed in both the Upper and Lower Basins.
  • Options to augment supply, such as desalination, are also needed under nearly all plausible future conditions.

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Interview

Studying the Colorado River Basin

David Groves

David Groves, Ph.D., is a senior policy researcher at the RAND Corporation and a core faculty member at the Pardee RAND Graduate School. He specializes in the development and use of exploratory modeling and robust decisionmaking methods for long-term policy analysis. His primary practice areas include long-term natural resource planning in the water resources, energy, and coastal ecosystem restoration and flood risk mitigation sectors. He is currently leading a portion of the technical analysis evaluating potential climate impacts on Africa's infrastructure plans for the World Bank. Recently, Groves co-led RAND's two-year long effort to support the U.S. Bureau of Reclamation's Colorado River Basin Study. He also led the RAND team that developed the planning framework and decision support tool that was used to support Louisiana's 2012 Comprehensive Master Plan for a Sustainable Coast. He has worked with numerous other water agencies in the United States to develop climate adaptation plans, including the California Department of Water Resources, the Metropolitan Water District of Southern California, Colorado Springs Utilities, and the New York City Department of Environmental Protection.

Jordan Fischbach

Jordan Fischbach, Ph.D., is a policy researcher at the RAND Corporation and a core faculty member at the Pardee RAND Graduate School. His research focuses on climate change adaptation, risk analysis, infrastructure planning, and developing and applying exploratory modeling and robust decision methods to better manage long-term uncertainty. He recently led a two-year storm surge and damage assessment for Louisiana's 2012 Comprehensive Master Plan for a Sustainable Coast, for which he was awarded a RAND President's Choice Award.

What challenges did the Basin Study Team face when trying to assess the River's supply and demand imbalances over the coming 50 years?

A key challenge was that future Colorado River flows and water demands are deeply uncertain. Due to climate change, the historical record of flows is not a reliable guide to future conditions. Therefore, the Study Team developed six demand scenarios and thousands of supply projections to describe how the system could play out over the next 50 years. The RAND team helped apply a new method for decisionmaking under uncertainty, called Robust Decision Making, to identify and describe the key vulnerabilities and then evaluate how different strategies could reduce those vulnerabilities.

What are the key vulnerabilities to the Colorado River Basin?

While the full study estimated the future performance of the River system using over 30 different metrics, just two key metrics were found to characterize the main vulnerabilities well.

A Lee Ferry Deficit--which occurs if the 10-year average flows past the border between the Upper and Lower Basins (in Arizona) falls below a critical level--would trigger reductions in water use in the Upper Basin. Estimating how frequently such a deficit would occur in the future is an excellent indicator for the Upper Basin conditions. We found that in many of the climate change futures such an event would happen frequently.

The elevation of the surface of Lake Mead, on the other hand, is a critical metric for the Lower Basin. If the Lake Mead pool elevation drops below another critical threshold, deliveries to Lower Basin users would be dramatically curtailed. We found that this condition would happen even in futures in which hydrologic conditions are similar to those in the recent history.

What strategies were examined to reduce these vulnerabilities?

The Basin Study evaluated dynamic water management strategies--those that implemented different options over time depending on how severe the Basin's imbalance was estimated to be. Each future led to a different set of options to be implemented and thus different costs. By modeling strategies in this innovative way, we were able to provide a better estimate of which options would be needed and different future conditions than modeling traditional static strategies. For example, in extremely dry futures, the strategies would implement more options than in wetter futures.

The RAND team developed a decision support tool to help the stakeholders define strategies that included only those options that had the characteristics desirable for different stakeholders. One strategy included options that would augment supply even during dry periods, whereas another excluded options that required significant amounts of energy.

What are the next steps for addressing the Colorado River management challenges?

The analysis showed that there are several options that are needed right away, including additional municipal and industrial water conservation and wastewater reuse. There are other options, such as desalination of various non-freshwater sources and agricultural conservation with transfers, that are needed in the coming decade but those will require significant planning and investment. Toward that end, Reclamation and the Basin State study partners are exploring implementation issues in working groups. If the current drought continues another year, however, one can expect that the barriers to implementation will start to fall.

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Robert J. Lempert

Applying Robust Decision Making: Planning for Water and Flood Risk Management

Robert J. Lempert

graphic from robust decsion making video

Robust Decision Making: Enabling Policymakers to Plan for the Future

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