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<br />Fourth Evaluation <br /> <br />In 1987, a fourth evaluation study entitled "Evaluation of Operational Cloud Seeding in <br />Western Kansas'" was prepared by the U.S. Bureau of Reclamation. The seeding time <br />period for this study was 1975-1985 and the no-seed time period chosen was 1948-1974. <br />It should be noted that cloud seeding operations were being conducted during 1972-1974 <br />in Northeastern Colorado, Northwest Kansas and Southwest Kansas; hence there were <br />some cloud seeding activities occurring in the study areas during the last three years of <br />the no-seed time period. <br /> <br />Seasonal precipitation was obtained for May through August each year'- since cloud <br />seeding during this time period always started on or before May 1 and always extended <br />until at least August 31. The primary data set for precipitation data was from the. <br />National Climatic Data Center. <br /> <br />The target area included ali 16 counties that had participated in the Western Kansas <br />Weather Modification Program for at least one year during the 1975-1985 time period. <br />A total of 14 target area weather stations, with at least an 18-year record of precipitation <br />between 1948 and 1974, were selected to represent the target area. However, five of <br />these 14 stations were located in counties that did not participate in one or more years <br />of cloud seeding activities during the 1975-1985 seeding period. <br /> <br />Three control areas were selected for the study. Because the majority of storms affecting <br />the target area move from a generally northwest or southwest direction, the researchers <br />apparently decided that only weather stations west of 10l"W would be considered for <br />selection in order to minimize the potential of downwind CODmmination occurring in <br />control area counties. A northwest control area consisting of counties in Northwest <br />Kansas, Southwest Nebraska and Northeast Colorado was selected. Precipitation in this <br />control area would have been impacted by other cloud seeding operations which were <br />discussed above and occurred from 1972-1979. A western control area located in <br />Southwest Colorado, Northeast New Mexico and Northwest Oklahoma was also selected. <br />A third control area was selected, which consisted of a group of 16 stations located west <br />of 101"W for which the correlation coefficient between each station's seasonal <br />precipitation and the mean seasonal target area precipitation was 0.67 or greater, based <br />on data from 1948-1974. lbis third control area included stations from the two other <br />control areas. <br /> <br />The sndy results showed that precipitation in the target and control areas was less during <br />1975-1985, when Western Kansas weather modification activities were occurring and the <br />precipitation deficiency in the target area was more pronounced. Their ultimate <br /> <br />· Dennis, Arnett S., Richard L. Eddy, and Roy M. Rasmussen, Evaluation of Ooerational <br />Cloud Seeding in Western Kansas. Final Reoort, November 1987. <br /> <br />6 <br />