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<br />SUMMARY OF PREVIOUS EVALUATIONS ON PRECIPITATION ENHANCEMENT <br /> <br />The Western Kansas Weather Modification Program was put into operation in 1975 and <br />several evaluation efforts have been made prior to 1994. <br /> <br />First Evaluation <br /> <br />In February, 1978 the Colorado International Corporation released a report entitled <br />"Conclusions and Recommendations Derived from an Operations Analysis of Western <br />Kansas Weather Modification Program". Page 58 of this report contains the statement: <br />"We cannot put any quantitative measure to the rain increase effort. There is just not <br />any data base available to provide for such analysis." I This report indicates that the <br />average annual cost for the first three years of operation, i.e. 1975-1977, was about <br />$200,000. Based on an assumption that cloud seeding operations increased rainfall by <br />1" and using crop yield data from North and South Dakota, thereport contains the <br />estimate that a 1" increase in rainfall would produce about $16,660,000 of increased crop <br />production, which would be a 83 to 1 benefit;to cost ratio. <br /> <br />Second Evaluation <br /> <br />In October, 1981, a second evaluation study entitled "The Assessment of Statistical- <br />Physical Techniques for the Evaluation of Weather Modification Operations" was <br />prepared by the Illinois State Water Survey Division for the National Science Foundation. <br />The time periods studied were 1931-1971 (pre-seeding period) and 1975-1979 (seeding <br />period). Monthly and seasonal rainfall data from April- September were obtained from. <br />National Weather Service stations. The target area consisted of all 15 counties that <br />participated in the programs at least one year during the 1975-1979 time peripd. The <br />control area consisted of 12 neighboring counties in Colorado, four in New Mexico, 10 <br />in Texas, 12 in Oklahoma and 25 in Kansas. The report states that "the statistical <br />evaluation on the rainfall observations indicated that there was a non-significant reduction <br />of rainfall in the target area during the seeded period. "2 <br /> <br />The results from the October, 1981 report should be interpreted with great caution for <br />a number of reasons, such as: a) three of the 15 target area counties did not participate <br />in cloud seeding operations each year , b) additional cloud seeding operations were being <br /> <br />I Colorado International Corporation, "Conclusions and Recommendations Derived from <br />an Operations Analysis of Western Kansas Weather Modification Program," (February 1978), <br />p.58. <br /> <br />2 Hsu, Chin-Fei et ai, Illinois State Water Survey Division, The Assessment of Statistical- <br />Phvsical Techniques for the Evaluation of Weather Modification Ooerations, (October 1981), <br />p. 41. <br /> <br />4 <br />