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<br />1. INTRODUCTION <br /> <br />Background <br /> <br />There is an ongoing debate as to the efficacy of cloud seeding as a means of precipitation <br />enhancement. Although much money has been spent over decades in support of cloud <br />seeding to increase precipitation, science has been able to conclusively demonstrate <br />strong evidence of which seeding techniques produce positive effects in only a limited <br />number of weather situations. In the over half-century since cloud seeding <br />demonstrations began, substantial progress has been made in understanding the natural <br />processes of weather. Some voice concern that the scientific challenges of proving <br />seeding effects have been found to be significantly more formidable and complex than <br />initially perceived and proof is elusive (National Research Council (NRC), 2003). <br />However, many others believe that despite the difficulty in objectively quantifying the <br />absolute values of seeding effects, it has been established that certain aspects of the <br />weather, specifically cloud microphysical and precipitation processes, can be <br />intentionally modified with beneficial effects and without detrimental environmental <br />effects. The large body of positive indications reported by many (Weather Modification <br />Association (WMA), 2004) references in this paper, as well as a multitude of analyses in <br />the literature constitute a collective positive signal. The overarching premise of this <br />paper is that cloud seeding does work, but both sides of the argument are provided here <br />for consideration by decision makers. <br /> <br />There are several reasons why WxMod has been pursued: fog and stratus dissipation; <br />hurricane strength reduction; lightning reduction, hail suppression, and precipitation <br />augmentation. This document focuses on the use of winter orographic WxMod for <br />precipitation enhancement to augment water supply. <br /> <br />History <br /> <br />The first laboratory and field experiments by Vince Shafer, Irving Langmuir, and Bernard <br />Vonnegut began in the mid-1940s and were known as the "Cold Box" experiments. <br />There was much enthusiasm and the positive results from cloud seeding and the potential <br />for producing rain were widely distributed. The combination of excited scientists, an <br />interested media, and a receptive populous resulted in a worldwide commercial industry <br />focused on cloud seeding, and an era of great interest among scientific organizations and <br />government. By 1951, weather modification programs were operating in about 30 <br />countries. <br /> <br />Wild claims of effectiveness led to differences in opinion as to the economic benefits of <br />cloud seeding and Congress held hearings on the matter between 1951 and 1953. It was <br />learned that millions of dollars were being spent annually by fanners, utilities, ranchers <br />and other users on weather modification activities covering approximately 10 percent of <br />the nation's area. As a result, the Advisory Committee on Weather Control was <br />established by an Act of Congress of August 13,1953. <br /> <br />-1- <br />