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<br />o <br />~ <br />Q') <br /> <br />'. ':} <br /> <br />~ <br /> <br />generator locations due to the limited population of the area, therefore, the effects <br /> <br />from those ground generators would be limited. In fact, ground generators were not <br /> <br />installed in Nevada (upwind of the area) until the second year of the project. <br /> <br />Aircraft seeding has also been utilized since 1975 but these seeding tracks are east <br /> <br />of the control. Finally, the previous NAWC evaluation suggested that little seeding <br /> <br />effect had been observed in the western desert regions since the ratio of observed <br /> <br />to predicted precipitation in that area was near unity (.96). <br /> <br />In spite of the above reasons, it is recognized that the use of this area as <br /> <br />a control could introduce a bias. However, unless seeding has caused a reduction <br /> <br />in the precipitation in the control area, by using this region ,as a control the <br /> <br />effect of the bias would be to reduce the apparent seeding effect in the targets <br /> <br />rather than enhance it. For all of the above reasons, therefore, this control area <br /> <br />was considered acceptable. The fact that the average precipitation observed during <br /> <br />the non-seeded historical period and the seeded period for the stations that make up <br /> <br />the control is nearly identical (1.69 inches'in the not seeded period to 1.68 inches <br /> <br />in the seeded period) would seem to indicate that the area selected is stable and <br /> <br />generally unaffected by seeding. <br /> <br />DEFINITION OF TARGET AREA <br /> <br />Those areas that were selected for evaluation were limited to the high yield <br /> <br />portion of the project near the control. It is recognized that seeding has been <br /> <br />conducted in southeastern Utah, but only since the 1975-1976 season and this area <br /> <br />is far removed from the western control area. Therefore, it has not been included <br /> <br />in this evaluation. An area in Arizona would probably be a more representative <br /> <br />control for southeastern Utah, although much of this region lacks stability in regard <br /> <br />to stations with long-term records. Portions of Tooele County have also been seeded <br /> <br />since the 1975-76 season, although this area has not been evaluated due to the <br /> <br />shorter period of operations (i.e., three years instead of five years of seeding). <br /> <br />- 4 - <br />