WMOD00319

• Title: North American Interstate Weather Modification Council - Fiscal Year 2009 Request
• Prepared By: McClintock Associates, Inc.
• Date: 1/1/2007
• Weather Modification - Doc Type: General Information

Focal Points

DROUGHT AND WATER SHORTAGES

Growing season dryness and droughts typically reduce U. S. crop production between 10 and
15 percent, with losses exceeding 30 percent in extreme years like 1988. These reductions may
increase in some areas as a result of global climate change. Such water shortages also have serious
impacts on municipalities and industry.

The application of atmospheric resource management technology to enhance rainfall and
snowpack for water supplies, and to reduce the direct effects of drought has recently seen a
significant upsurge in much ofthe western United States. In just the past decade, rainfall enhancement
activities in west and south Texas have expanded from 2.2 million acres annually, to over 48 million
acres. Programs have recently started in Idaho and expanded in Colorado. New Mexico is also
considering expansion of its operation program.

As populations continue to increase steadily in many chronically water-short states, and as
agriculture is always water sensitive, cloud seeding may likely prove to be an economically sound,
environmentally- friendly means of moderating future shortfalls. Studies indicate precipitation can be
significantly increased through the seeding of winter clouds in the western United States. Initial
measurements indicate that snowpack accumulations and subsequent runoff is increased by an average
of 10-15 percent. A conservative economic evaluation of this effort suggests the cost of the
additional water is less than ten dollars per acre-foot.

Recent experiments have shown that timely and well-targeted treatment can yield sizeable
increases in rainwater from summertime cumuliform clouds. In addition, these efforts have begun to
document the physical processes within the vigorous, supercooled, cloud towers at the time of
treatment. It is now believed that a cloud's amenability to treatment is strongly dependent on cloud-
base temperature.

A recent assessment by Texas Tech University researchers of the four major crops in the
Texas High Plains indicates that a 21 percent increase in rainfall during the growing season would
result in an economic gain of $349 million each year. With a very large water-conservation district
spending about $500,000 annually for a cloud seeding program to enhance growing season rainfall in
the region, this gain in regional economic output represents a return of $700 for each dollar being
invested in weather modification technology. Recent estimates of the efficacy of rain-enhancement
cloud seeding in west Texas indicates a 21 percent increase is well within the capabilities of the
technology.

More fieldwork, coupled with computer modeling of cloud processes, is needed to
corroborate and further refine the recent findings. Ultimately this will result in the development of
decision trees, to aid those conducting operations in fine-tuning their methodology, and in ensuring
that untimely, ineffective, and/or inappropriate seeding be avoided. The research needs to be

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