Scientists See Looming Water Crisis in Western US

Will Dunham, PlanetArk 1 Feb 08;

WASHINGTON - A water supply crisis is looming in the western United States thanks to human-caused climate change that already has altered the region's river flows, snow pack and air temperatures, scientists said.

Trends over the past half century foreshadow a worsening decline in water, perhaps the region's most valuable natural resource, even as population and demand expands in western states, researchers led by a scientist at the Scripps Institution of Oceanography wrote in the journal Science on Thursday.

Up to 60 percent of changes in three key factors affecting the West's water cycle -- river flow, winter air temperatures and snow pack -- are due to human-caused climate change, they determined using multiple computer models and data analysis.

"Our results are not good news for those living in the western United States," wrote the team led by Tim Barnett, a climate expert at Scripps Institution, part of the University of California at San Diego.

"It foretells of water shortages, lack of storage capability to meet seasonally changing river flow, transfers of water from agriculture to urban uses and other critical impacts."

Barnett said computer models point to a looming crisis in water supply in the coming two decades.

It has been clear for some time that the climate has been changing in the western United States, and the question was whether it was due to natural variability or driven by climate change related to human-produced greenhouse gases and aerosols, the scientists said.


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While the western United States has experienced natural wet and dry cycles in the past, current water flow trends differ in length and strength from past natural variations, the scientists found. The changes match those expected from the impacts of human activity on climate.

The researchers tracked water flows in three major western river systems -- Columbia, Colorado and Sacramento/San Joaquin rivers.

Changes over the past half century have meant less snow pack and more rain in the mountains, rivers with greatly reduced flows by summer and overall drier summers in the region, they noted.

"At this point in time, there's not much we can do to change that," said Barnett, who worked with experts at the US government's Lawrence Livermore National Laboratory, the University of Washington in Seattle and the National Institute for Environmental Studies in Japan.

"We're going to have to adapt our infrastructure and some of our societal needs to fit the way the world is changing," Barnett said in a telephone interview.

"Water shortages throughout the west, hydroelectric power reductions, heat waves -- the whole litany of things that go with global warming."

Another group of researchers, writing in the same journal, said leaders who set water policies worldwide must take climate change into account when planning for the future.

Until now, water policies have relied on the premise that historical water patterns could be counted on to continue. But human-induced changes to Earth's climate have begun to shift the averages and the extremes for rainfall, snowfall, evaporation and stream flows, Christopher Milly of the US Geological Survey and colleagues said.

"Our best current estimates are that water availability will increase substantially in northern Eurasia, Alaska, Canada and some tropical regions, and decrease substantially in southern Europe, the Middle East, southern Africa and southwestern North America," Milly said in a statement.

(Editing by Maggie Fox)

U.S. Western Water Supplies Already Altered by Global Warming
Andrea Thompson, LiveScience Yahoo News 31 Jan 08;

When it rains, it sometimes still pours out West. But it's not enough.

Changes in the western U.S. water supply, such as a declining snowpack and rivers running dry in the summer, can mostly be attributed to human-caused climate change, a new study finds. These changes will require a new approach to water management in the West in the future, scientists say.

Water supplies for much of the West come from winter snowfall that accumulates in mountainous regions and melts throughout the spring and early summer, flowing into the rivers that wind throughout the western states.

Over the past 50 years, researchers have noted significant changes in this system of water flow, which a new study, detailed in the Feb. 1 issue of the journal Science, attributes to global warming.

Warmer and drier

Over the last half-century, less snow has accumulated on mountains throughout the winter months. This snowpack is critical to maintaining the main sources of river water in the spring and summer months in the arid regions of the West.

The snowpack that does exist has been melting earlier than it did in the past as the spring thaw creeps backward. This forces all the water that would be available from the melt to flow through the rivers faster and earlier than it used to. So while water might once have flown from western rivers through June, leaving only July and August as dry months, the snowpack might now be gone by April, tacking on three more months to the dry season.

"The rivers get rid of the water they have for the year earlier," said study leader Tim Barnett at the Scripps Institution of Oceanography in San Diego.

The study used climate and hydrological models to pin down the cause of these changes and found that the length and strength of the changes over the last 50 years can't be explained by natural variations, the authors say. Instead, human-caused global warming is the culprit.

Mega-droughts have struck the West in the past, but these droughts have been caused by the onset of climate conditions that decreased the amount of precipitation falling over the area. But global warming has created a wholly different scenario, driven by increasing temperatures, not decreasing precipitation.

The warming atmosphere is causing precipitation to fall over the mountains as rain rather than snow. The rain runs straight off into rivers, so instead of having water stored as snow into the summer, water availability peaks earlier in the year.

Another effect of global warming has been to push back the start of spring so that snows begin to melt earlier in the year.

The models Barnett and his team ran show that up to 60 percent of the trends in water flow observed from 1950 to 1999 can be attributed to human effects, mainly global warming.

Growing drier

The authors write that their "results are not good news for those living in the western United States."

Previous studies using climate models have projected that even more arid conditions will become the norm for the Southwest over the course of the next 100 years, which will only compound water woes, the authors of the new study say.

In another article in the same issue of Science, a group of hydrologists call for the need to revise the way water management is done in the West.

Currently water resources are allocated based on the idea that water flow in the future will be just like it was in the past, with some natural fluctuations. But the observations over the past 50 years and the predictions for the future now require a shift in the way water management is done.

"Water management needs to take on some new ideas and methods in the way it does business," said one of the authors, Christopher Milly of the United States Geological Survey.

Accounting for the shifting distribution of water over the seasons and the region's increasing dryness will require change on a number of fronts, Milly says, including changing the computational tools water managers use, changing some of the existing water infrastructure, shifting water use from agriculture to urban areas, conservation, and possibly even slowing the rapid development of some southwestern cities.

People blamed for water woes in West
Erica Werner, Associated Press Yahoo News 1 Feb 08;

Human activity such as driving and powering air conditioners is responsible for up to 60 percent of changes contributing to dwindling water supplies in the arid and growing West, a new study finds.

Those changes are likely to accelerate, says the study published Thursday in Science magazine, portending "a coming crisis in water supply for the western United States."

The study is likely to add to urgent calls for action already coming from Western states competing for the precious resource to irrigate farms and quench the thirst of growing populations. Devastating wildfires, avalanches and drought have also underscored the need.

Researchers led by climate expert Tim P. Barnett at the Scripps Institution of Oceanography at the University of California, San Diego, studied climate changes in the West between 1950-1999. They noted that winter precipitation falls increasingly as rain rather than snow, snow melts faster, river flows decrease in summer months, and overall warming is exacerbating dry summer conditions.

The researchers used statistical modeling to compare climate changes that would have happened with natural fluctuations over time, to climate changes with the addition of human-caused greenhouse gases and other emissions from vehicles, power plants and other sources.

They found that most changes in river flow, temperature and snow pack between 1950 and 1999 can be attributed to human activities, such as driving, that release emissions including carbon dioxide and other greenhouse gases into the atmosphere.

The changes they observed differed significantly from trends that could be attributed to natural fluctuations between wet and dry periods over time, they said.

"The climate's changing in the West. We've known that. The question is why, and no one's really addressed that," Barnett said in an interview. According to his study, "The answer is it is us."

"The picture painted is quite grim so it's time to collectively sit down and get our act together," Barnett added, suggesting the need for conservation, more water storage, and a slowdown on development in the desert Southwest.

"The building is just going crazy, so it would be a pretty good idea to put a curb on that unless they can figure out how to get more water," he said.

The study also included researchers from Lawrence Livermore National Laboratory, the University of Washington, Seattle, and the National Institute for Environmental Studies in Japan.

"Our results are not good news for those living in the western United States," they conclude. The research "foretells of water shortages, lack of storage capability to meet seasonally changing river flow, transfers of water from agricultural to urban uses and other critical impacts."