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B-1 B. EVALUATIONS OF RECENT PROJECTS We were asked to do what we could to re~examine and discuss the most important experi- ments involving rainfall enhancement conducted recently. Earlier experiments were discussed in the reports of the National Academy of Sciences and National Research Council (MacDonald et ai, 1965) and (Malone et al, 1973). The material that follows covers those experiments in the list given us for which data was reasonably accessible. Without the support provided by three experienced meteorological statisticians -- Glenn Brier, Paul Mielke, a.nd Ronald Biondini -- who went over reports and papers in (;onsiderable detail and prepared summaries according to the outline given in Section 46 of the Appendix, we would have been unable to prepare the discussions that follow. At a late stage, we were asked, again with the aid of Drs. Brier, Mielke. and Biondiini, to also reconsider the Climax II experiment. The results will be found in Section 45 (in the Appendix) . 7. Skeletal descriptions * Florida area cumulus expl~riment * This randomized exploratory study , (FACE), conducted over a large area of south central Florida during the p,eriod 1970-1976, involved dynamic seeding of "suitable" clouds during each summer season. Throughout the course of the experiment, seeding entailed the firing of airborne AgI flares (but see 9. Operational Changes and Difficulties). Rainfall estimates were based upon radar rea.dings, in most years adjusted by measures from rain gauges'. The study was designed to be a "double-blind" experiment (but see 8. Dangers of Subjective Influences). Over the course of the study, there were 98 experimental days, 52 seeded and 46 not seeded. * national hail research exp1eriment * This study (NHRE) was planned to be conducted over the period 1972.1976.' Blocked randomization was employed, with block size two. The study was carried out during summer seasons in Colorado., Effects of cloud-based seeding within updrafts with AgI flares were assessed from hail-s~lparator and hail-pad records in the target area. NHRE was terminated prematurely, in 1974, since physical measurements colle(;ted prior to that time failed to sUPlPort the hypothesis of hail suppression due to seeding. The study embodied 57 experimental days, 27 seeded and 30 unseeded. * Colorado River Basin pilot project * This project, randomized by 24-hour days, was designed, among other objectivl~S, to confirm suggested efl'ects from Climax and Wolf Creek experiments, all of which were winter studies conducted in the San Juan Mountains of Colorado. The project was completed during five successive winter seasons -- 1970-71 to 1974-75 -- wIth a total of 306 experimental days. * Israeli cloud seeding experiment II * This confirmatory study was based upon findings of Israeli experiment I (1960-1967), that had suggested rainfall increases, due to seeding, of approximately 15 percent in the target area. The study was conducted during win.ter seasons, 1969-1975. Days were selected randomly for seeding or no seeding on a 50-50 basis, prior to each season. In data analysis, a day was (;On- sidered to be "seeded" if it had been (randomly) scheduled for seeding, whether or not seed- ing operations actually were conducted.