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OTC launches new Colorado River Simulator

November 14, 2007
by John Weisheit

Two weeks ago the Bureau of Reclamation released its first ever plan for managing the Colorado River under shortage conditions. However, their strategy is based on a narrow set of assumptions that underestimate the potential for future shortfalls, and the risks to the region's $1.7 trillion economy.

Using the same techniques employed by Reclamation's forecasters, the Colorado River Open Source Simulator (CROSS)* has been developed to allow the public the opportunity to explore a more complete range of scenarios which nature may have in-store for Colorado River water users.

Click here to download CROSS

CROSS's simple interface is designed for anyone to use, whether familiar with the Colorado or not, says Niklas Christensen, who developed the simulator for OTC and is releasing it today at the American Water Resources Association's annual conference in Albuquerque. Most importantly, using the same inputs, CROSS outputs validate well against Reclamation's far more sophisticated and expensive model, making this a credible and valuable public tool in this era of Colorado River uncertainty.

As a leading scientist on assessing the impact of climate change on the hydrology and water resources of the Colorado River, Christensen is fully aware of the risks that may lie ahead for the watershed. Results from his research, funded by the Department of Energy, predict up to a ten percent reduction in flows by the end of the century. Findings by other scientists, such as Martin Hoerling from the National Oceanic and Atmospheric Administration, predict the change could be much greater and come more quickly, up to a 40 percent reduction in flows by the middle of the century.

None of us can say with precision what's going to happen, but what the science is telling us is that something very likely will, and it's quite surprising that such an important variable has been omitted from Reclamation's shortage forecasting, adds Christensen.

CROSS shows that a reduction in the middle range of predictions, 20% by the year 2100, would render it highly unlikely that Lake Mead, the nation's largest reservoir, would ever fill again, and a strong likelihood of being empty for good by 2050. By contrast, Reclamation's shortage assumptions have Lake Mead holding steady throughout their 2008 - 2060 forecast period. Worse still, should flows mimic what the basin has experienced so far this century, CROSS shows how Lake Powell, the Nation's number two reservoir, and Lake Mead would likely become operationally empty within the next five years.

"With the region in its longest recorded drought, and reservoirs at below 50% capacity, it's amazing that Reclamation modelers assume the Colorado of the future will likely mimic its high flow periods of the past," says Owen Lammers, Executive Director of Living Rivers. With every drop of water already allocated, and just a 2% mistake equivalent to losing Las Vegas' Colorado River water supply, providing the public with comprehensive forecasting is no trivial matter.

Even if climate change were not an issue, Reclamation's forecasts still errors toward the positive. Current estimates of the long-term annual flow of the Colorado River range from 13.0 to 14.7 million acre-feet (maf). Reclamation's forecasting is largely based on flows of 15.0 maf--the recorded average streamflow from 1900 - 2005. These 20th century flows, however, are now recognized to be among the wettest in 1,200 years. While Reclamation acknowledges this, and has conducted some alternative analysis with flows as low as 14.6 maf, it failed to examine the full range of variability offered by researchers.

CROSS illustrates how at 14.0 maf Reclamation's new shortage policy will be immediatly taxed, very likely requiring consultation with the Secretary of Interior to determine who gets what water and when, the precise action these polices were designed to avoid. At 13 maf, the new system collapses altogether with Lake Mead likely operationally empty by 2020, rising for only brief periods through the rest of the century.

"It's not that we feel such scenarios are any more valid than what Reclamation has offered, its just their omission misrepresents the potential for shortages that science suggest we ought to acknowledge", stresses Lammers. Fortunately with CROSS, anyone can explore the full range of possibilities, as well as the amount of water conservation we can employ to successfully navigate any uncertainty.

*CROSS requires the use of Microsoft Excel installed on a Microsoft Windows operating system. CROSS is designed to be a self-contained application and does not require the user have previous experience with Microsoft Excel.

We would like to remind everybody that a hydrological model is what humans have created, rather than what really happens in nature.

Additional information:

Comment letter and water budget of April 2007 by Living Rivers on the Draft EIS of Interim Guidelines

Scripps Institute press release of February 2008 "When Will Lake Mead Go Dry?"

Paper by Scripp's Pierce and Barnett

Reclamation web page: Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations for Lakes Powell and Mead


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