WMOD00597

• Project Name: Sierra Ecology Project
• Title: The Sierra Ecology Project - Volume II - Workshop IV, Workshop V
• Date: 7/1/1980
• Weather Modification - Doc Type: Report

INTRODUCTION

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The Water and Power Resources Service, U.S. Department of the Interior, is conducting, as
part of its Project Skywater, a multiyear study of the effects of weather modification by seeding
winter orographic clouds over the American River Basin in California's Sierra Nevada. The
SCPP (Sierra Cooperative Pilot Project) is designed to determine the effects of cloud seeding
upon the water yield and the ecology of the basin. At the request of the Water and Power
Resources Service, Cooper et al. [1]1 recommended certain investigations needed to assess the
ecological impacts of the pilot program. The Service then contracted with the Pacific Southwest
Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture, Berkeley,
California, to study the effects of cloud seeding upon the ecology of the affected area. Forest Ser-
vice personnel will also study effects upon snowpacks and subsequent water delivery to streams.
The study will use data from within the basin and from the Forest Service CSSL (Central Sierra
Snow Laboratory), north of the basin.
Part of the research, particularly that dealing with possible effects upon the basin's human
population, will be done under contract by others. For example, the study of the effect of addi-
tional snowfall upon highway traffic movement has been coordinated with the California Depart-
ment of Transportation.
The ecology of an area is the result of the long-term interaction of parent geologic material,
climate, vegetation, and animals. Cooper et al. [1] recognized the problems inherent in trying to
study the ecological responses to a short-term change in precipitation. The evaluation is further
complicated because the effects of increased precipitation and snowpack are superimposed upon
an enormous mosaic of natural and man-caused disturbances.
The effect of a 5- to 7 .5-percent increase (estimated 10 to 15 percent increase reduced by 50 per-
cent randomization) in the annual precipitation on the ecology of the area from a 7- to lO-year
program will not be detectable through normal plot-type studies. Due to the overall complexity of
the problem, a preliminary "best estimate" assessment of the prospective ecological responses to
weather modification was needed before any research was conducted. As part of its studies, the
Forest Service brought together teams of scientists to assess the impacts of snowpack augmenta-
tion upon five fields, including vegetation, deer and their habitat, forest insects and diseases,
hydrologic processes, and lake and stream biota. Experts in each of the necessary academic
disciplines examined the problem areas for: (1) an assessment of the probable impact of
snowpack augmentation upon their area of interest, and (2) an evaluation of research and
monitoring needs for assessing impacts.
This report is the result of a 4-day workshop which evaluated the potential for weather
modification to alter hydrologic processes within the American River watershed in the region
above 1220 m (4000 ft) elevation. It is expected that cloud seeding will be conducted from the
1220-m (4000-ft) elevation level to the crest of the Sierra. The workshop was held September 5-8,
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1978, at Berkeley, California, and was attended by six scientists familiar with weather modifica-
tion techniques, soils, water, and nutrient relationships in the American River Basin.
Biographical data on the participants are listed in the appendix.
Following a discussion of the assumptions under which this analysis was made, three main sec-
tions evaluate,: (1) the alteration of inputs to the watershed - including particulate matter,
macronutrients, heavy metals, and other constituents; (2) changes in water movement and the

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INumbers in brackets refer to items in the bibliography included as part of the appendix at the
end of this report.

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