Severe AZ water shortage possible

Since the middle 1980s, many climatologists, hydrologists and other scientists have predicted that global warming and other forms of climate change will mean less water for the Colorado River and, by extension, the Central Arizona Project, the $4 billion collection of canals and pipelines that is Arizona's water lifeline.

But few experts have belted that message as forcefully as Barnett, a marine physicist at Scripps Institute of Oceanography in San Diego.

His warnings have been met with doubt by some of the West's water managers who have long felt they could plan, design, engineer and manager their way out of a future water crisis caused by the collision course between population growth and the region's aridity. Some scientists questioned Barnett's first study, which predicted that Lake Mead and Lake Powell had a 50 percent chance of drying up by 2021 due to human-caused climate change. In the second study, like the first co-authored with fellow Scripps researcher David Pierce, he predicts that by 2050 the river could see water flow cut in half in some years due to human-caused climate change and natural variation in precipitation.

Since Arizona has the lowest priority of any of Southwestern state for Colorado River water — California is legally entitled to get its entire share before Arizona gets any — that kind of shortage could curtail CAP deliveries to Tucson and Phoenix by one third to one-half for up to 10 years in a row.

Barnett has been a messenger of global-warming gloom for years. Four years ago, he told the now-defunct Knight-Ridder newspaper chain: "The debate is no longer whether there is a global warming signal," after his analysis of ocean-temperature and salinity readings showed that the oceans had heated at rates predicted by computer models, two-thirds of a degree Fahrenheit from 1969 to 1999. "The debate is what are we going to do about it."

The Star talked with Barnett last week after the release of a new study published in the Proceedings of the National Academy of Sciences:

Q: Why did you do this latest study?

A: We looked the first time at the reservoirs going dry. Well, that's a fairly esoteric notion. Some water people said you didn't include this and you didn't account for that in making your conclusions. We went back this time and we included all that stuff, and the answers don't change. Well in the process, we really thought that this time we really oughta look at deliveries of water.

Q:. Why?

A: It's a much more people-oriented kind of result than an abstraction. What does the average person say, "Hey, Lake Mead will go dry?" That's something. But when you say, people will be on water rations, that's a different story. We tried to do something socially more important.

Q: What makes this question of global warming's impact on water so important?

A: It's this population growth and what that means in terms of additional water. You've got the scenario of Mother Nature coming back to normal, with a lower flow in the river, after so many wet years. You've got human-induced climate changes in the water budget in the West that will reduce runoff into the river. But according to the census, the seven states in the Colorado River Basin will have nearly 24 million more people in 2030 than they did in 2000.

Q: What will that mean?

A: One acre foot of water supports two families of four. With 24 million more people living here, we're looking at the need to pull three million acre-feet out of today's supply. Where is that going to come from?

Q: Is your new paper a retreat from your earlier prediction that Lake Mead could dry up by 2021?

A: I'd say the new numbers are simply refinements. You'll recall from paper one that the 2021 number for Lake Mead was at one extreme of a range that depended on several assumptions which we said were poor, for example, the dumb water-manager assumption that they would do nothing to mitigate their problems in advance of the reservoir drying up. The point is that there is a range in the times, dependent on assumptions. You should not be stuck on a single number.

Q: What should officials do to prevent a water crisis?

A: They should start now and get together a group of water managers and say, "What if these two guys are right?" In my book, the best solution is to reduce development, put a cap on it. No politician I talk to wants to talk about that.

Q: State officials are looking hard at other solutions, like desalination of brackish groundwater and cloud seeding. Do they deserve any credit for that?

A: With desal, what do you do with the salt slurry left over in the middle of the desert? These other sources -- has anyone put a cost estimate on them? It might be very sobering to do.

Q: Do you feel optimistic that we'll heed your warnings here in the Southwest?

A: Do I think anyone will get off their butt in the next five years, take the initiative and do long-range planning? No. In the long term, five to 10 years and out, anyone who knows anything will know there is a problem and we have to do something about it.

some of the findings from the new study:

• The planned future deliveries of Colorado River water to the seven river basin states, including Arizona, generally aren't possible by 2050 because of global warming and a return to historical river flows after unusually high levels during the 20th century.

• If climate change reduces river runoff by 10 percent, the requested water deliveries to the states will exceed the amount that can be delivered sustainably by 2040. If runoff is off 20 percent, the water demands will start exceeding supplies by 2025.

• Lake Mead, previously predicted to have a 50 percent chance of going dry by 2021, now is seen as having a 50 percent chance of being 8 percent full by 2025 or 2042, depending on various assumptions about river flows and water deliveries.

• Depending on how much runoff is reduced, the amount of river water available for delivery by 2050 could be cut to as little as 8.4 million acre feet*, compared with about 15 million acre feet in most of the 20th century.

• The water shortfalls could be managed with reuse of sewage effluent, conservation, transfers between users and other measures, but continued population and economic growth will aggravate the problems and make balancing water demands and supply much harder.

* An acre-foot is 325,851 gallons or enough water to serve one to three families for a year.

Source: "Sustainable water deliveries from the Colorado River in a changing climate," by Tim Barnett and David Pierce, Scripps Institute of Oceanography.