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precipitation amounts. In California, one project's decision to seed was based on runoff and existing reservoir storage. Reservoirs, raingages, and streamflow stations were monitored to supply data on which to evaluate the potential for flooding by rainfall.

Comparison With Prior Year's Data

The analyses of the reported data for CY 1974 and 1975 have been compared to determine trends and salient features in weather modification activities. Table 7 shows this comparison. Even though the analyses are based on incomplete information, the partial lack of data is consistent and comparison is justified. Data for the two years are similar. Major decreases over the previous year were found in cumulative number of modification days, hours of airborne operations, and gallons of liquid propane used. Major increases showed up in the amounts of silver iodide and polyelectrolyte used.

Table 7.--Comparison of weather modification activity
data for CY 1974 and 1975

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The 72 nonduplicative weather modification activities reported to NOAA for CY 1975 have been summarized herein. Fourteen of these activities were Federally sponsored and 58 were nonfederal.

One commercial operator carried out about one-fourth of the activities. Analysis of the reports also shows that local community associations sponsored about one-third of the projects. Precipitation increase accounted for about one-half the activities, hail decrease and fog dispersal nearly one-sixth each, and research about one-sixth of the efforts.

During the year, weather modification activities were planned in 25 States; California and Oklahoma had the greatest number of activities with eleven and nine respectively. Total target area for all activities was

about 163,000 mi2, with South Dakota, Utah, and North Dakota having the largest target areas. Federally sponsored weather modification accounted for about 7 percent of the total target area.

The number of ground-based techniques and aircraft delivery methods were about equal. The liquid-fueled generator or burner continued to be the most commonly used weather modification apparatus for ground and air operations; the arc-type silver-iodide burner was operated solely at ground level. Silver iodide was the nucleating agent in 50 activities, while dry ice was used in 12.

During CY 1975, the total of modification days was estimated to be 1800; the total for fog modification was 88 days. Weather modification apparatus operated from ground level for about 47,000 hours and from aircraft for 1,662 hours. Nearly 1,600 kilograms of silver iodide were dispensed, a little more than half during nonfederal ground-based operations and about a third during nonfederal airborne activities. Nearly 21,000 kg of dry ice, 1,300 kg of polyelectrolyte, and about 5,600 gal of propane were expended during fog dispersal efforts.

Comparison of the data for CY 1974 and 1975 showed little change in overall level of effort. The number of reports, sponsors, operators, distinct projects, and States involved were about the same as were target area, hours of ground operation, and dry ice used. The major differences were a decrease in modification days, hours of airborne operations, and amount of liquid propane during CY 1975. About 50 percent more silver iodide was dispensed in CY 1975 than in CY 1974.

Consideration of project safety and environmental impact continued to be an important part of most reported activities. There were no indications of interference of a Federal research program by a nonfederal activity during the year.

REFERENCES

Charak, M.T. and DiGiulian, M.T., Weather Modification Activity Reports November 1, 1972, to December 31, 1973, National Oceanic and Atmospheric Administration, Rockville, Maryland, March 1974, 38 pp.

National Oceanic and Atmospheric Administration, Summary Report Weather Modification, Fiscal Year 1973, National Oceanic and Atmospheric Administration, Rockville, Maryland, December 1974, 154 pp.

National Oceanic and Atmospheric Administration, Weather Modification Activity Reports, Calendar Year 1974, National Oceanic and Atmospheric Administration, Rockville, Maryland, March 1975, 37 pp.

Interdepartmental Committee for Atmospheric Sciences, National Atmospheric Sciences Program, Fiscal Year 1976, ICAS 19-FY 76, National Science Foundation, Washington, D. C., May 1975, 82 pp.

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