WeatherMod Cloud Seeding Guidelines

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"The long-term irreversible effects of weather modifica- tion on circulation patterns and the weather itself should be negligible. Weather patterns develop and move in systematic fashion and are dominated by the effects of the oceans and the continents. The effects of weather modification activities are local and transient - there is no evidence that cloud seeding causes anything more than generally small and short-term weather changes. StUdies have indicated that most of the seeding material is recovered in the immediate precipitation area - the remaining material is rapidly diluted by the normal diffusive turbulence in the atmosphere - and that the effects of cloud seeding activities should not be expected to 'extend any great distance from the target area. Consequently, the very small changes in local weather caused by cloud seeding should have no effect on the forces driving the general atmospheric circulation and its associated weather systems". (17) One of the most important goalS of both researchers and operational users in weather modification is to obtain more accurate estimates of the precipitation increases obtainable through cloud seedi,ng. It has been demonstrated that seeding can increase precipitation from certain cloud types. Theoretical models of cloud development with simulated seeding have provided results that agree with field exp~riments for certain classes of clouds. Although there has not been a definitive research program to confirm final results, estimates of precipitation from commercial seeding projects range from increases of more than 100 percent over a period of a month to decreases of 20 percent or more. Notwithstanding frequent criticism of these estimates, there is a consensus among scientists that there is a potential for seasonal increases of 10 to 30 percent (18). 2.3.2 Impacts of Mammals. The impact of weather modifica- tion of mammals can occur in two ways. The first and most 2-l0