Rainfall Enhancement Technique Tested In Drought-Ridden Mexico
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Scientists from the National Science Foundation-funded National Center for Atmospheric Research in Boulder, Colorado, are engaged in new research that will bring more credibility to the science of weather modification--and possibly some rain to the drought-ridden Mexican state of Coahuila.
Working with scientists from several Mexican universities, the researchers are beginning the first field trials in North America of a new technique for seeding clouds to enhance rainfall. Field trials are planned for June to October over the next four years in Coahuila. The researchers will also transfer cloud-seeding technology to Mexico and train Mexican scientists in its use and evaluation.
"The technique tested in Mexico this summer uses pyrotechnic flares mounted on aircraft to seed clouds," explains Jewel Prendeville, coordinator of NSF's lower atmospheric facilities section. "While the aircraft flies at the base of the cloud, moisture-retaining particles produced by the burning flares rise into the cloud. As the cloud's water vapor is attracted to the particles, droplets are formed, which then fall out as rain. The wide range of droplet sizes produced by the particles encourages and accelerates the precipitation process."
This method of cloud seeding was first tried in 1990 in South Africa. There it appeared to increase rainfall by 30 to 60 percent over what would have occurred without the seeding.
Cloud seeding has been practiced at various places in the world since 1946, but most experiments have produced inconclusive results. The initial optimism that soared in the 1950s and 1960s has given way to a much more cautious approach over the last 20 years. Although there have been many rainfall-enhancement programs around the world during the last two decades, most have lacked a solid scientific basis and have had no means to validate the results of the seeding. Because of the natural day-to-day variability of clouds across geographical regions, it has been difficult for scientists to isolate the effects of seeding.
Brant Foote, director of the center's research applications program, is coordinating the overall research program that will test and validate the new seeding method. He cautions that it is too early to tell whether the seeding technique will be broadly applicable to Mexico or any other rain-deficient area. "The results in South Africa are striking," says Foote, "but there is no guarantee of success elsewhere. These efforts are clearly still in an early phase. We anticipate that this research in Mexico will help us better understand the physical processes that lead to increased rainfall."
The research program includes the following components:
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