Thursday, July 6, 2006 | 7:24 a.m.
The elusive dream of making rain may still be impossible, but decades of research is proving that a once-maligned technology really can pump up how much precipitation comes from the clouds.
Researchers believe that "seeding" clouds with chemicals may be a way to increase precipitation and augment depleted Colorado River reservoirs, the main source of Las Vegas' drinking water.
The Southern Nevada Water Authority in May authorized spending $750,000 on two consultants, CHM2Hill and Black & Veatch, to investigate different ways to augment the drought-struck river. The options would include such relatively humdrum methods such as removing salt-cedar, a pernicious weed taking over the banks of wetlands throughout the river's basin.
Cloud seeding is also getting a fresh look.
"We can't dismiss out of hand some of these new technologies," said Ken Albright, Water Authority resource director. "We think it's a viable option for further research."
The study should be done next summer.
Cloud seeding actually has been around for at least 60 years. Essentially, the idea is to add tiny particles - usually silver iodide - into clouds. Ice forms around the particles, and the growing seeds of ice eventually fall to Earth as snow or rain. The particles can be added to clouds from aircraft, by ground-fired rockets or from remote-controlled sites high on mountains.
The effectiveness of cloud seeding, however, is debated. The federal Bureau of Reclamation, which controls the giant reservoirs at lakes Powell and Mead and the lower half of the Colorado River, says that cloud seeding would have only limited effect on the huge river system.
Assistant Interior Secretary Mark Limbaugh, who heads the bureau, cautioned against "weather modification" efforts at a June 20 conference in Boulder, Colo.
"While we are looking at ways to increase water supplies, we are considering a cautious approach to the use of weather modification," Limbaugh said at the conference, which was devoted to weather modification technologies, particularly cloud seeding. "The scientific work so far has not been able to measure - and therefore has not been able to demonstrate - that weather modification activities effectively produce additional water supplies."
Limbaugh noted that the Colorado River and its reservoirs are less than 60 percent full, and water managers fear the return of sustained drought. Nonetheless, the federal government has to be careful where it spends its money, he said, and the uncertainties of cloud seeding make it a poor candidate for federal dollars:
"We are in a time of limited federal funding - that is a reality that we all have to deal with. We have to get the most 'bang for the buck' in terms of stretching water supplies in the Colorado Basin."
The federal focus will be on conservation, storage agreements called "banking" among river states, infrastructure investments to stop unintended water loss and continued research, Limbaugh said.
"Even though some are suggesting that weather modification may show promise as a management tool, we must continue to focus on the tools that are working for us today," he said.
Others believe the research shows more promise.
A study for the Upper Colorado River Commission, which manages the Colorado River from Lake Powell north, finds that cloud seeding in the Rocky Mountains could provide five times the water Las Vegas uses. The study, delivered in March and prepared by the private North American Weather Consultants Inc., a member of the Weather Modification Association, suggests that areas targeted for the technology could see increases in precipitation from 5 percent to 15 percent - with a total potential payoff of almost 1.4 million acre-feet.
Las Vegas draws 300,000 acre-feet from the Colorado River to satisfy most of the urban area's water needs. One acre-foot is about 326,000 gallons.
The seeding cost, according to the Upper Colorado River Basin study, would be $7 million annually, or about $5 per acre-foot. In contrast, the Water Authority spends about $300 to bring an acre-foot to municipal distributors in the Las Vegas Valley.
In October, the Metropolitan Water District of Southern California, which supplies most of Southern California, found similar results. Cloud seeding could produce between 1.1 million and 1.8 million acre-feet in the upper basin and another 830,000 acre-feet in the lower basin, the agency reported.
Other groups and scientists, including the American Meteorological Society, agree that at a minimum, cloud seeding needs more research.
The positive chorus is no surprise to Arlen Huggins, a Desert Research Institute scientist who has been working on the technology for 19 years.
Nevada has funded research into cloud seeding as far back as the early 1960s, said Huggins, who works at the institute's Reno campus. The DRI's ongoing efforts include seeding to increase Nevada's mountain snow pack, especially to increase spring flows in the Truckee River and to Pyramid Lake.
Huggins said it has been difficult to quantify how much cloud seeding has contributed to the Northern Nevada effort, but the DRI also is participating in a $8.8 million, one-year study in Wyoming that could help put numbers to the cloud-seeding operations.
So far, the results "have been quite promising," he said. "We'd like to show a 10 (percent) to 15 percent increase in precipitation."
Huggins said research also is countering some past concerns.
One concern of those who depend on precipitation downwind of cloud seeding is that water claimed in one area is lost to another. But Huggins said the total amount of water carried in storm clouds is huge, with only a small portion of that coming down as precipitation.
"You're taking a little bit of the cloud water vapor, 1 percent of the total amount of water in a storm," he said.
And, Huggins said, the silver in the silver iodide used for cloud seeding isn't an environmental concern: "We've pretty much put to rest the issue of environmental effects from silver in the snow. Even after doing cloud seeding for years, we've not added significantly to the silver that's in the streams and ground water in the West."
Most cloud-seeding efforts, such as the ones in Nevada, are very local, but Huggins sees potential in activity on a multistate level.
"The projects that are there now are seeding just a fraction of the watersheds that could potentially contribute," he said. "What we'd all like to see, those of us in this area of research, is that some agency of the federal government gets on board with the research."
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