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<br />. <br /> <br />SECTION IV. PRESE~T STATUS OF TEC~~OLOGY <br /> <br />Since the late 1940's. numerous e%perimental anc operationaL weather <br />modification programs have been conducted to increase precipitation <br />in the mountains of the uestern United States. Although they were <br />conducted over a wide range of topographical and meteorological <br />conditions, they all traced their beginnings to the studies of <br />Bergeron 10/ and LudLam 11/. They were designed either co produce <br />additionar-precipitation O;-to investigate the means by which addi- <br />tional precipit4tion could be produced. All of these projects were <br />based on the physical concept of making the natural precipitation <br />process more efficient by ice-phase seeding. <br /> <br />Proiect Back~round <br /> <br />Of tbe numerous projects conducted in the western United St~tes, <br />four have had the most impact and are of most interest in the <br />pl~nning of this Colorado River Basin Program. They are the <br />Climax experioent, the ~olf Creek Pass experiment, the Colorado <br />River Basin Pilot Project, and the Sierra Cooperative Pilot Project. <br />These projects were conducted under different criteria and in <br />different locations. A brief description of each program and a <br />summary of the initial and reanalyzed results are presented to <br />provide an historical perspective for the proposed program. <br /> <br />Climax Experiment <br /> <br />The Climax experiment consisted of two consecutive 5-year phases <br />(Climax I, 1960-1965, and Climax II, 1965-1970) conducted by <br />Colorado State University to investigate mountain clouds and the <br />modification of their precipitation processes. The experimental <br />area was located in the central Colorado Rockies near the town of <br />Leadville. The experimental design consisted of randomized blocks <br />of seeded and nonseeded 2~-hour experimental units. The suitability <br />of any experimental unit was based upon a forecast made by the <br />National Weather Service of precipitation at Leadville. Seeding <br />was conducted with ground-based silver-iodide/acetone generators <br />located varying distances upwind of the Fremont Pass target area. <br /> <br />. <br /> <br />the evaluation was based on precipitation data froo 65 project- <br />operated sites in the target area and eight National Weather <br />Service control stations outside the target area. Three statistical <br />methods -- a two-sample Wilcoxon test, a two-sample sum of squared <br />ranks, and a parametric test described by Tham ~/ -- were used <br />to evaluate the difference in precipitation between seeded and <br />nonseeded periods. The ~o phases of the experiment were evaluated <br /> <br />IV-l <br />