WMOD00011

• Applicant: Don Griffith North American Weather Consultants, Inc.
• Sponsor Name: City and County of Gunnison
• Project Name: Cloud Seeding Evaluation
• Title: The Development, Conduct and Evaluation of a Cloud Seeding Program for the Gunnison River Basin, Colorado During the 2003-2004 Season
• Prepared For: City and County of Gunnison
• Prepared By: North American Weather Consultants
• Date: 8/1/2004
• County: Gunnison
• Weather Modification - Doc Type: Report

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regression equations. The precipitation evaluations were based upon a 15 season period while the
snow pack evaluations \\'cre based upon 20 seasons.

If the indication of a 13-1-4% increase in 3vera2e snow water content is reasonably
accurate, the an'rage increase in the tar-get area would be approximately one inch.
Although 1.00 inch of water may nol sound significant at first thought. that amount of
additional water distributed equally onT the approximately 30DO-square mile \','atershed
would equal approximately 160,000 acre feet of additional water. There would likely be
some losses of some of this additional water to evaporation/ground water recharge. If half
of this estimated amount resulted in surface runoff (80.000 acre feet), the cost of this
additional streamflow \'muld be approximately SI per acre foot. This analysis would
perhaps provide a conservative estimate of the potential impact of the program since these results
are from a below nonnal water year. The results. assuming that the 13-14% increases are
representative. would be higher in average and abovc average water years.

The precipitation (and snowpack) in much of western Colorado has bcen below nonnal
for the past seven winter seasons. Because of this drier-than-nonnal period. ground water has
been depleted. The western United States is known for its frequent periods of drought. In
addition. in many areas of the west, water supplies even in "nonnal" years do not meet the
demand for water in these areas. Consequently. we usually recommend that our clients consider
conducting cloud seeding projects on a routine basis each year. This has proven to be very
effective approach in southern and cenLral Utah. where operational cloud seeding has been
conducted in 24 of the past 25 winter seasons. Contractual provisions can be made to suspend or
tenninate the cloud seeding projects in very high water years. when additional water may not be
beneficial. \Ve recommend this approach for several reasons:

. No one can accurately predict if precipitation during the coming winter season will be
above or below nonnal. Having a cloud seeding program already operational will take
advantage of each seeding opportunity.

. Seeding m normal to above normal water years will result in a larger precipitation

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