The Southwest will continue to face costly water shortages over the next century if leaders in the region fail to take more aggressive steps to cut water use, especially as climate change further shrinks already limited supplies, according to a new study from an environmental think tank.

Even now, water demand in the Southwestern states -- Arizona, California, Nevada, New Mexico and Utah -- threatens to exceed available supplies in some areas, and groundwater is being pumped "well beyond the sustainable rate," according to the report, "The Last Drop: Climate Change and the Southwest Water Crisis."

Meanwhile, climate models predict warmer and drier conditions in the coming decades at the same time more people flock to the sun-drenched region.

"Add the impacts of growing population and incomes, and the Southwest will face a major water crisis in the coming decades," the report's authors warn, noting that people with higher incomes tend to use more water. "Current trends in water use cannot possibly be continued," they added.

A new report predicts that the Southwest will continue to experience water shortages regardless of policy steps taken to reduce the impacts of climate change. Photo courtesy of the Arizona Department of Water Resources.

As climate change turns the region even drier and hotter, water demand will rise even further, according to the report from the U.S. Center of the Stockholm Environment Institute, a nonprofit research affiliate of Tufts University.

"Climate change could be adding 25 percent to the total shortfall of water over the next century, which is quite a lot of water," said Frank Ackerman, who co-authored the report with fellow SEI economist Elizabeth Stanton.

If the five Southwestern states do not "take prompt action" to scale back water usage, the region will face a combined shortfall of 1,815 million acre-feet of water from population and income growth alone. When the effects of climate change are factored in, that figure jumps by another 282 million to 439 million acre-feet, warns the report.

"Over the coming century, unchecked climate change would worsen the Southwest water crisis, imposing additional costs on the region of up to a trillion dollars," the report's authors conclude. "This is, of course, only one part of the worldwide impacts of climate change -- but it is one that could make all the difference for the communities of the Southwest."

The researchers drew upon dozens of studies from the last decade and three new computer models to analyze water usage, shortfalls and water costs into 2110 for the five states. The region relies primarily on the Colorado River and groundwater to meet their water needs.

All of the models show "water demand outstripping water supply in the near future," according to the report.

"Climate policy choices we make today are not just about exotic environments and far-future generations -- they will help determine how easy or hard it is to create a sustainable water system in the most arid region of the country," Ackerman said.

Solutions

Echoing similar studies, the report concludes that the five states should implement major conservation and efficiency measures for both urban and agricultural water users. They also suggest phasing out low-value crops, some of which are worth less than the water used to grow them, according to the report.

Increasing groundwater extraction is not feasible because there is not enough groundwater available, and building desalination plants or importing water is too expensive and impracticable in many areas, the report says.

But as the threat of water scarcity looms, water managers are already starting to see those more expensive options as increasingly attractive. For instance, Nevada has a project underway to import groundwater from the Nevada-Utah border, and Arizona and the federal government hope to restart the Yuma Desalting Plant near the Mexico border (Land Letter, May 6, 2010).

"When it comes to water supply, how much is too much [to pay]?" said J.C. Davis, a spokesman for the Southern Nevada Water Authority, which supplies water for the Las Vegas area.

Technological advances will continue to make desalination plants and state-of-the-art water treatment plants, which can recycle effluent, more cost-effective in the future, said Mitch Basefsky, a spokesman for the Central Arizona Project, which distributes 1.5 million acre-feet of Colorado River water to urban and agricultural users in three Arizona counties.

"That's not to say a crisis isn't going to come," he added. "There may be shortages in parts of the Southwest, and with climate change, there may be a new normal on the Colorado River. But there's really no way to know for sure what's going to happen in the next 100 years."

And both cities and farmers are already taking steps to stretch existing water supplies, primarily through conservation and improved efficiency, Basefsky added.

"If you look at the period between 2002 and 2010, Las Vegas's population grew by about 400,000, but our water use dropped by 26 billion gallons a year," Davis said.

Basefsky pointed out that in Arizona and elsewhere, state and federal water managers are already encouraging farmers to increase efficiency through measures such as lining irrigation canals and timing diversions differently.

Whatever solutions states adopt, they must act quickly if they are to avoid the worst consequences of climate change, the report's authors conclude.

"The cost of inaction, of waiting for unplanned shortages, is difficult to predict in advance, but it would be large and painful; it would involve unexpected, unplanned disruptions and losses," they wrote.

Click here to read the report.

Reese writes from Santa Fe, N.M.