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<br />Dlinois. Data were obtained for the years the project was in the field and for the preceding years <br />back to 1948. Most rainfall and crop-hail data were obtained on magnetic tape to facilitate <br />processing by computer, but some crop-hail data were available only in printed form and had to be <br />entered into the computer by hand. <br /> <br />The rainfall and crop-hail data were processed on a Perkin-Elmer 3245 computer at the DARR. <br />Two foons of the rainfall data were studied: (1) the observed values of precipitation at sites with <br />reasonably long observation periods and (2) interpolations from the observed data fitted to a grid. <br />The seeding data and the crop-hail data were fitted to the same grid. The grid extends from 35.5 <br />to 41.0 ON and from 96.0 to 104.0 oW. It includes much of Kansas and parts of five adjoining <br />states. The grid spacing is 15 minutes of latitude by 15 minutes of longitude (approximately 28 km <br />by 22 kIn, but the width increases from north to south). <br /> <br />The results of the statistical analyses of rainfall patterns show that the changes in rainfall due to the <br />seeding program, if they exist at all, are much smaller than the natural variations that took pJace. <br />Much of the target area had less growing-season rainfall during the seed years (1975-85) than <br />during the no-seed years (1948-74). This fact should not be attributed to the seeding, however, <br />because the same tendency was noted over much of the surrounding, unseeded, study area. <br /> <br />The results of the analysis of crop-hail data are more favorable than those for the rainfall data. <br />Although they do not prove that the seeding has suppressed hail, they are consistent with the <br />hypothesis of a hail suppression effect. The evidence suggests that the apparent effect is <br />concentrated in the eastern part of the target area and extends beyond its northeastern boundary, <br />The suggested suppression effect is a reduction in crop-hail damage of some 25 to 50 percent. <br /> <br />The part of the target area with the most favorable hail experience during the seed years also shows <br />a tendency toward drier weather during those years. However, an analysis of hail/rain ratios <br />indicates that the tendency toward drier weather was not sufficient to account for the lessened hail <br />damage. <br /> <br />Comparison of the hail damage pattern with the location of the actual seeding operations shows the <br />area of most favorable results to be centered about 100 kilometers (60 miles) east of the area <br />receiving the highest amounts of seeding materials. This distance corresponds to over 2 hours of <br />travel of a typical seeded storm. <br /> <br />The final section of this report discusses the Kansas results in the light of results from other rainfall <br />stimulation and hail suppression projects and makes some conunents on possible future courses of <br />action. <br /> <br />2.PROffiCTOPERATIONS <br /> <br />The Western Kansas Weather Modification Project has the dual purpose of rainfall increase and <br />hail suppression (Smith [3]). It was designed to use the latest techniques for cloud seeding, and <br />the operational procedures were subject to revision each year. The seeding devices, seeding <br />materials, and seeding rates changed several times in the 1975-85 study period. The target area <br />also changed as counties elected whether or not to participate on a year-to-year basis. Figure 2.1 <br />shows the western third of Kansas and names the counties that participated at any time during the <br />11 years used in this study. Table 2.1 indicates the participating counties for each year. <br /> <br />... <br /> <br />3 <br />