WMOD00287

• Title: The National Weather Modification Plan
• Prepared For: CAO Subcommittee on Weather Modification
• Prepared By: The Working Group of the CAO Subcommittee on Weather Modification
• Date: 2/13/1981
• Weather Modification - Doc Type: Report

are sim1lar to those of Montana and on other days are similar to those of
Texas. Results from the Montana and Texas programs can, therefore, be
extended to the Kansas cloud systems.

Several studies of the impact of additional rainfall in Montana, Kansas,
and Texas have demonstrated the importance to agriculture of timing and
frequency of rain as well as the total amount. In general, an increase in
growing-season precipitation increases agricultural production, but not every
crop benefits from additional rain at a particular time. Evidence indicates
that rainfall augmentation could alter the competitive advantages of crops
within a region and among regions". Consequently, benefits should be evaluated
on regional and even national scales. The information gained from this work
is giving direction to future development of the precipitation management
technology.

2. Sierra Cooperative Pilot Project CFY 1980--$2.4 Million)

The Sierra Cooperative Pilot Project is comprehensively investigating
maritime stonns in the Sierra Nevada to detennine the potential for increasing
precipitation and subsequent water supplies through cloud seeding.

Preliminary planning for the SCPP began in 1972 with initial focus on the
California Sierra. The area of interest was later expanded to include western
Nevada. This phase emphasized public involvement and the social and
environmental impacts of weather modification in the Sierras.

The research phase of the project began with a review of previous
experiments in the Sierra Nevada and a careful selection of the project study
area, which includes the American River Basin on the western slope of the
Sierra Nevada and the Truckee-Tahoe Basin on the eastern slope. Physical
studies of candidate cloud systems are being conducted to determine their
seedability and frequency of occurrence and to generate a testable
modification hypothesis for the experimental design. Tracing and diffusion
studies are being carried out with seeding tests to determine appropriate
seeding materials and rates. Limited analysis and interpretation conducted on
a 4-year data set indicate that seeding opportunities are much less frequent
and less apparent than had been expected.

Detailed analysis efforts, with limited field activity, are planned for
the 1980-81 period to assess the degree of seedability of various cloud types
and their frequency of occurrence. By the fall of 1981, the results of the
analyses will be incorporated into a design plan for future activities in the
field, expected to resume in the winter of 1981-82. With completion of the
calibration experiments and the experimental design, a randomized a~ploratory
study will be conducted on individual cloud types. Subsequent phases of the
project will include large-scale seeding and a rigid confi~atory test.

3. Colorado River Basin Project CFY 1980--$0.3 Million)

The technology of modifying wintertime orographic cloud systems to
increase mountain snowpack'has been developing over the past 30 years.

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