WMOD00470

• Project Name: Project Skywater
• Title: Environmental Impacts of Precipitation Management: Results and Inferences from Project Skywater
• Date: 6/6/1977
• Weather Modification - Doc Type: Report

...

[Reprinted from BULLETIN OF THE AMERICAN METEOROLO(;ICAL SOCIETY, Vol. 58, No.6, June 1977]
Printed in U. S. A.

Environmental Impacts 01
Precipitation Management:
Results and Inferences from
Project SkYWater

Wallace E. Howell

Division of Atmospheric Water Resources
Management
Bureau of Reclamation
Department of the Interior
Denver, Colo. 80225

Abstract

Recent completion of several research projects into weather
modification impacts on the environment provides an op-
portunity for placing this subject in a new perspective.
Studies of physical and biological processes relating precipi-
tation and ecosystem changes show relatively few discernible
effects, all of them minor in nature and magnitude. Direct
effects of nucleating agents no longer appear consequential.
Since no acute problems have surfaced, the focus is likely to
shift to possible long-term effects on ecosystems as a whole,
where changes associated with natural precipitation gradients
and climatic fluctuations provide a model for those to be
expected from precipitation management. The weakness of
environmental impacts of weather modification compared to
the consequences of other human actions renders it unlikely
that these impacts will be decisive within a behavioral frame-
work.

1. Introduction
Following issuance of the report of the Special Com-
mission on Weather Modification of the National Science
Foundation (1966), investigation of environmental im-
pacts became a recognized part of Project Skywater's
program for developing an acceptable as well as an
effective technology of precipitation management. A
problem analysis undertaken for Skywater by Cooper
and Jolly (1969) was followed by three major field pro-
grams of environmental research-one completed in
1975 (Knight, 1975) and two in 1976 (Steinhoff and Ives,
1976; Armstrong and Ives, 1976)-and by several ana-
lytical studies of agricultural and economic impacts. In
addition, a Programmatic Environmental Statement for
Project Skywater (Bureau of Reclamation, 1976a) is
scheduled for distribution in mid-1977.
These several reports provide the basis for a new
assessment not only of the environmental impacts of
the Skywater program but also of the widespread and
prolonged application of the two precipitation manage-
ment technologies with which it is concerned-winter-
orographic snowpack enhancement and summer-convec-
tive shower stimulation in the mountains and the Great
Plains of the western United States, respectively. The
review that follows is addressed to the impacts of these
two technologies (which are jointly referred to as pre-
cipitation management) as distinguished from other de-
veloping and potential technologies, such as hail suppres-
sion and the modification of tropical maritime clouds,
and from other precipitation technologies, such as
winter-nonorographic cloud seeding.
Field activities of Project Skywater with potential for
environmental impacts have run at a typical rate during

488

the past decade of 100-300 modification-days per year
(summed over all projects) over study areas typically
from 3000 to 10000 km' in extent. The most important
have been the San Juan, Pyramid Lake, Wasatch,
Bridger, and Jemez winter-orographic projects and the
North Dakota, South Dakota, and High Plains Co-
operative Program (HIPLEX) summer-convective proj-
ects. Other field activities were of shorter duration, less
intensive operation, or smaller extent and dispersed
relatively small quantities of seeding material.
Environmental studies under Skywater, totaling nearly
$3 million, are shown in Table 1. Following the prob-
lem assessment by Cooper and Jolly, two groups of
studies were planned. The first, addressed to physical
and biological effects, was planned in cooperation with
a group of advisors assembled under the leadership of
Colorado State University (Teller et al., 1970) and led
to the establishment of three major field investigations-
the San Juan and Medicine Bow Ecology Projects and
the Avalanche Research Project-and a few minor ex-
perimental projects of a supporting nature. The second
group of studies was addressed to economic and social
impacts, necessarily of a more analytic nature since di-
rect intervention with the economic and social systems
that might be affected by precipitation management was
not possible.
In addition to these programs, minor studies have
been completed in support of the Sierra Cooperative
and HIPLEX programs. In November 1976, Skywater
sponsored a week-long interdisciplinary conferen.ce at
Vail, Colo., devoted to all major aspects of precipitation
modification impact, which included a nested conference
on seeding agents cosponsored by the National Science
Foundation.

2. Impact of widespread and prolonged
applications of precipitation management
Far less concern has been expressed over the effects of
Skywater and other field experiments than over the pos-
sible impacts of the widespread and prolonged precipita-
tion management programs that would presumably fol-
low successful conclusion of them. Indeed, the greater
part of current studies focuses upon this broader ques-
tion, even though Skywater has been and continues to
be a program of technological development without
authorization for operational applications.
Expectations of impact from widespread and pro-
longed application are based on a set of explicitly stated

Vol. 58, No.6, June 1977