Document Type

Report

Publication Date

12-1991

Abstract

The Bureau of Reclamation conducted a feasibility study of seeding winter mountain clouds as a possible means of enhancing the water supplies of the Sevier River Basin of Utah. A considerable body of pertinent meteorological observations from in or near the basin is examined. The evidence indicates that Utah winter mountain clouds often have more supercooled liquid water available than is naturally converted to snowfall. Thus, the needed "raw material" for cloud seeding to be effective is frequently available. Much of the excess liquid water has been found in the lowest kilometer or less over the mountain barriers, a region that can be seeded with properly located ground generators. This zone is too warm for silver iodide seeding during some storms and other agents, such as propane, should also be considered. Past operational and experimental seeding projects in the region are examined. There are suggestions from some analyses that seeding has produced about 10 percent more precipitation on a seasonal basis. However, other analyses have disputed these suggestions and it is concluded that the question of the effectiveness of current seeding practices is still an open one. It is recommended that a two phase demonstration program be conducted to place the emerging technology of winter cloud seeding on a firm scientific foundation. Physical experiments should be emphasized which document all key links in the chain of physical processes following seeding. Benefit-cost ratios for an operational seeding program are estimated with the caveat that a number of assumptions need further testing. However, if seeding could produce additional snowfall even approaching 10 percent per winter, the value of the additional water would likely exceed, and perhaps far exceed, the cost of seeding operations.

Comments

R-91-10

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