|
<br />~J J'. ~ r--
<br />v ~: .;;. "! J a
<br />
<br />regular part of water resource management in Gunnison County, depending on results from the 2002-2003 season's operation,
<br />which will take place January through April, and November through April for the four years of the program, The program cost is
<br />$85,000 for the 2002-2003 season,
<br />To "seed" clouds, silver iodide is introduced into the clouds where super-cool water droplets adhere to the silver iodide
<br />particles and freeze, These ice embryos begin to grow, and if conditions are favorable, may turn into snowflakes, This part of the
<br />process is called the static seeding effect. The process mimics natural processes in which substances in the air, such as soil particles,
<br />can act as ice-forming kernels that initiate the freezing process, Cloud seeding has been used for about fifty years to answer
<br />agricultural needs; ski resorts like Vail have been seeding clouds for twenty years, A secondary effect of cloud seeding can occur
<br />as welL As the water droplets freeze, they release latent fusion heat, invigorating the clouds, Under the right circumstances, this
<br />can cause clouds to grow large and last longer than they would have had they not been treated, This part of the process is called
<br />the dynamic effect.
<br />According to studies by the Weather Modification Association, the American Meteorological Society and the World
<br />Meteorological Organization, additional precipitation resulting from cloud seeding operations is between five and twenty percent.
<br />Studies conducted by North American Weather Consultants on similar projects in Utah and Idaho show an increase of about ten
<br />to twenty percent.
<br />How can you tell if it would have snowed just as much without cloud seeding? Quantifying exactly how much it might have
<br />snowed during a certain year without intervention is "a difficult thing," admitted North American Weather Consultants
<br />meteorologist Dave Yordy To calculate results, meteorologists focus on "Snotel" sites, places where measurements have historically
<br />been taken, They average those measurements of precipitation for as many years as possible, and compare them to similar areas,
<br />Not all meteorologists advocate cloud seeding, Art Rangno is a research meteorologist in the Atmospheric Sciences
<br />Department of the University of Washington, and a former forecaster with the Colorado River Basin Pilot Project in Durango,
<br />Colorado, In the December 8, 2002 Durango Herald, Rangno wrote, "There is no evidence gained through rigorous scientific
<br />'randomized' experiments that snowfall is increased through cloud seeding,"
<br />The ability to detect the effect of cloud seeding on snowfall has been precluded by three crucial facrors, Rangno continued,
<br />"We still do not know how many ice crystals are already present in clouds; much less do we have the ability to predict how many
<br />there are going to be in advance, a requirement for cloud seeding success,"
<br />Furthermore, according to Rangno, it is virtually impossible to release the highly concentrated seeding "crystals" from the
<br />ground and have them arrive in the right clouds in the right concentrations, Nor can the clouds be over-seeded or under-seeded,
<br />and they must be seeded at the right temperatures so the seeding crystals will prosper, And if those requirements are not
<br />demanding enough, all this must happen at the right location upwind of a target so that the crystals and snow fall out on it.
<br />lastly, said Rangno, we cannot predict the amount of snow a storm will naturally produce; therefore when a storm is seeded,
<br />no one knows what seeding did, if anything, "Unfortunately," asserted Rangno, "this makes it easy to claim seeding effects that
<br />may not have occurred,"
<br />In Gunnison County, the silver iodide will be introduced at between eighteen and twenty different locations, spread out to
<br />maximize exposure, When conditions are deemed right, trained residents will turn on the propane-fueled cloud seeding
<br />generators that will spray silver iodide solution into a flame, The cylindrical generators are about three feet high and a foot and a
<br />half wide, and will be filled with about eight gallons of solution, The generators do not blast the solution into the clouds, rather,
<br />the flames vaporize the solution and winds carry the silver iodide up into the atmosphere, The silver iodide generally needs to
<br />reach an altitude of about 10,000 feet above sea level to be effective, The number and timing of releases depend on weather
<br />conditions. "Conditions have to be right," said North American Weather Consultants' Dave Yordy "We do the best we can judging
<br />things like wind current and wind direction,"
<br />What happens to the silver iodide after it snows? The silver iodide returns to the earth in tiny concentrations, The typical
<br />concentration of silver iodide in precipitation from seeded clouds is less than ,1 micrograms per liter, The US Public Health
<br />Service's acceptable concentration is 50 micrograms per liter,
<br />At a December 2002 public hearing for the cloud seeding permit, ranching interests expressed concern that seeding too early
<br />in the fall and too late in the spring could have a negative impact on cattle operations, To fully utilize north valley grazing, cloud
<br />seeding will not start until mid-November and will end early if there is good snowpack so as not to interfere with calving season,
<br />
<br />39
<br />
|