work everywhere, and there are indications that sometimes seeding produces decreases in snowpack. The Bureau's research program is making progress in clarifying just what the conditions are under which seeding can increase snowfall.

This requires knowing more and

more about the conditions of natural cloud formation, how the natural precipitation mechanism works, the condition under which it is deficient, and the condition under which seeding can be effective.

Skywater winter seeding projects have been conducted to find the strands of commonality of the physics that exist across differences in geographic location, terrain features, and types of storms. Concepts of how precipitation management works in winter mountains have developed substantially since the times when these experiments were performed.

The theoretical background and development of winter orographic seeding techniques have shown that the amount of water present in a cloud, the concentration of ice crystals in the cloud and the trajectories of snow and ice crystals relative to a mountain barrier are the most important factors needed to produce additional precipitation when artificial

cloud seeding techniques are utilized.

Because of their importance,

there is a requirement that measurable parameters be identified which

reflect these factors.

Results of various cloud seeding projects have reinforced the

theoretical concepts through the comparison of precipitation in seeded situations and nonseeded situations with the measured ranges of the physical parameters.

The Climax experiments conducted in central

Colorado under National Science Foundation sponsorship showed a 10 to 20 percent overall increase in precipitation due to seeding. Larger positive seeding effects (or increases in precipitation) were observed in a relatively warm range of estimated cloud-top temperatures with decreases for colder cloud-top temperatures.

The Colorado River Basin Pilot Project was conducted to show that selective seeding of clouds, based on seeding criteria developed from past projects, could produce useful quantities of additional snowpack over large areas. The analysis of data from this project verified many of the theoretical and physical factors and criteria developed in other projects for successful snowpack augmentation from cloud seeding.

When only those days that truly met the seedability criteria (based on all available data) were considered, seed-day precipitation exceeded no-seed-day precipitation by an important amount. Analysis of the experiment indicated that increases in the mountain snowpack were not at the expense of precipitation in the downwind valley. Rather, precipitation at the downwind valley gages apparently was increased under conditions conducive to increases at higher elevations.

The Western U.S. Water Plan report titled "Critical Water Problems Facing the Eleven Western States" recommends weather modification as the best immediate source of additional water for the Colorado River region. Behind this recommendation was much study of other alternatives. The report indicates spot water shortages can be expected in the Basin by 1985 and major shortages are anticipated by the 1990-1995 period.

A Project Skywater report prepared for the Western U.S. Water Plan provides estimates of the potential increases available in 12 major western river basins. The following map includes a summary of the study estimates of annual water increases for the Colorado Basin and bordering areas.

A meeting on the future of weather modification research in the Colorado River Basin with representatives of the governors of the basin states was held in Denver in December 1975. The importance of the Bureau continuing and expanding its research role was emphasized by those present. There was recognition that the actual increases still had to be confirmed and important questions in downwind effects, environmental impacts and identification of benefits to be resolved before major permanent commitments to operational cloud seeding could be made. Since the additional electrical generation by the cloud seeding water could produce an increase in power sales that could finance a large part of the Federal research costs, the possibility

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of including a research or "demonstration" project as an Upper Basin Participating Project was suggested. For this to be done, the

States would share by committing parts of the Upper Basin fund.

In response to locally perceived requirements for additional water in the northern Sierra Nevadas of California, a cooperative winter orographic cloud seeding experiment is now being planned and designed. Cooperation in the planning phase on social, environmental, hydrologic, and meteorologic studies has involved State agencies such as the Department of Water Resources, Department of Transportation, and the Highway Patrol, as well as the U.S. Forest Service and the Sacramento River Forecast Center.

The Bureau cosponsored an American Meteorological Society meeting in San Francisco in November 1975 to obtain the scientific community's input to the proposed program. It was concluded that a carefully designed, measured, controlled precipitation augmentation experiment in the Sierras is the most logical next step for a major effort in weather modification for both scientific and practical reasons.

V. Economic and Societal Interactions

Increasing recognition of the responsibility for assessing the economic and societal implications of technology led to inclusion in the Skywater program of studies of economic impact and utility of weather modification and of societal institutions and attitudes affecting and affected by its implementation.