Orange County Register

Lake Powell levels fell in the 2004 droughts. Researchers say worse time ahead could be remedied with sound management. (Image courtesy of Clyde Mueller/AP)

Orange County continues to grow in population and in water demand, but a crucial supply of Southern California drinking water — the Colorado River — could have a 50% chance of collapsing by 2057, a new study says.

This is a worst-case scenario forecast by researchers from the University of Colorado at Boulder. The scenario will happen if global warming reduces the water flow of the Colorado River by 20%, and if the current water consumption by Southwestern U.S. cities does not slow down.

Double Impact

With continued global warming, and without any changes to our rising urban water demand, we will have a one-in-two chance of having insufficient Colorado River water supply when 2057 rolls around. Aggressive reductions in our water use will only decrease our chance of depletion to one-in-three.

California is now in its third year of drought. Depending on the year, Orange County draws anywhere from 30% to 70% of our water from the Colorado River. Half of the water consumed in Southern California comes from the Colorado, which itself was hit by drought between 1999 and 2005. Lake Powell levels dropped 140 feet during that time.

However, whether climate change really will slash the Colorado’s flow by 20% is not known. Climate scientists estimate that global warming could cause Colorado River annual flow to drop anywhere from 6% to 20%.

If climate change only drops the Colorado’s waters by 10%, the study says that aggressive water use management should keep the depletion risk down to a one-in-ten chance, which is closer to natural, non-climate change risks of depletion.

Aggressive water use management would include rationing Colorado River water deliveries to downstream cities.

Continuing Research

The Scripps Institution of Oceanography published similar research last year. However, the 2008 paper reported that the Colorado will reach that 50% chance of depletion as early as 2021.

Scripps professor Tim Barnett, the lead author of the 2008 study, says the University of Colorado study largely uses the same water forecast model, but changes an important number in the equation.

“When Colorado reservoir levels reach severe lows, it triggers the Bureau of Reclamation to reduces the amount of water delivered to municipalities,” Barnett said. “If you deliver less amount of water, you’ll have more left to be rationed in the reservoirs for future use.

“Our research used a delivery amount consistent with the bureau’s policy. The new study uses [a lesser] delivery amount. If you forecast the future with this lesser number, of course you will find that the 50% reservoir depletion risk will be delayed years later.”

Nevertheless, Barnett says the new study is valuable by focusing on how water managers can respond to the upcoming problems with the Colorado River. The scenarios in this new study, together with previous analyzed scenarios, should provide a good picture of future water shortages and facilitate long-range planning by Colorado River water managers, says Barnett.

– Story by Ben Young Landis

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