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<br />- <br />{~; FAQs about Cloud Seeding to Augment Mountain Snowpack <br />"u" <br /> <br />Q. Wh)' do we need 10 augment ~nowpa('k'! <br />A. Snowmelt contributes 50-80% of Western reservoir water storage. Western snowpack has been declining <br />over the last 50 years. There is a growing body of evidence that air pollution is contributing 10 this decline. <br />Winter cloud seeding otTers a means to compensate for this trend. <br /> <br />Q. I)ocs cloud seeding for snowpack augmentation reall)' work'! <br />A. Yes! The Weather ;..1odification Association. World Meteorological Organization, American .\lclcorological <br />Society and the ~ational Academy of Sciences Report all slate that there is strong evidence for seasonal <br />precipitation increases over nalural precipitation on the order of 10%. To achieve such increases, well.designed <br />projecls 11Il1St be operaled 011 aiong-tam alld comilllling ha.\'is, /lUtjtt.\"t during drallghlS. Such projects will help <br />fill reservoirs for use during times of .b'Teater need, such as droughts. <br /> <br />Q. What are the em'ironmental and health effects or seeding material and its effect on clouds and <br />precipitation? <br />A. Minimal. The most common seeding material. silver iodide. is used in very small amounts. The typical <br />concentration of silver in rainwater or snow from a seeded cloud is less than one 0.1 microgram per litre (one <br />pan in 10.000.000.000). 111is is well below the acceptable concentration of 50 micrograms per litre. set by the <br />U. S. Public Ikalth Service Many regions have much higher concentrations of silver in the soil than are found in <br />precipitation from seeded clouds. The concentration of iodine in iodized salt used on food is far above the <br />concentration found in precipitation from a seeded stonn. An alternative seeding technology is the expansion of <br />liquid propane gas 10 freeze water in clouds: the amounts of this gas are also very minute. National <br />Environmental Policy Act compliance for all cloud seeding environmental impacts has been demonstrated by <br />past studies. <br /> <br />Q. Docs cloud sccdin~ decrease precipitation downwind. i.e.. "rob Peter to pa)" I'aul?" <br />A. ;-";0. The idea that rainfall illcreases in one area must be offset by decreases elsewhere is a misconception. <br />11\e amollnt of atmospheric moisture passing over a mountain barrier Ihat is convened to precipitation is usually <br />10% or Icss. If this natural precipitation is increased by 10% by cloud secding. only 1% of the original <br />atmospheric moisture supply is depicted. Moreover. winter cloud seeding is done on clouds on the upwind side <br />of mountain ranges. These clouds usually dissipate on the downwind or lee side of the range. via a nalural <br />process called the "rain shadow." This is the reason that lee side areas like the Colorado Front Range and <br />Nevada arc mllch drier than on the upwind side of the mountains. So the atmospheric moisture supply on the lee <br />side of the mountain range \vill not likely precipitate anyway. Finally, precipitation data from a number of long- <br />teon cloud seeding projects have been examined in detail for evidence of "extra-area" effects. There have been <br />no significant indications of precipitation decreases dowm...ind from any of these projects, in consonance wilh <br />what wc would expect from the rain shadow etYec!. <br /> <br />Q, 110" much does cloud seeding ('osr: <br />A. The cost of cloud seeding programs are on the order of SIO per acre-foot of water, varying slightly wilh the <br />value of water and the llses 10 which it is PUI. This eost makes it an attracli\"(' alternative to desalinization and <br />constmclion of new reservoirs. Given typical costs of water for agricultural purposes. cloud seeding lIchie\'l!s <br />benefit.to-coSI ratio.~ approaching 40 10 i. <br /> <br />Adapted in pan from the Weather ~Iodification Association's Facts Brochure. <br />http://weathennodific3Iion.orglfacts.hun <br />