WMOD00398

• Project Name: Project Skywater
• Title: Precipitation Management and the Environment - An Overview of the Skywater IX Conference
• Date: 9/1/1977
• Weather Modification - Doc Type: Report

IMPLICATIONS FOR THE SKYWATER PROGRAM
(W. E. Howell, Division of Atmospheric Water Resources Management)

The results of the Skywater IX Conference remain, at this time, to be better digested before
being converted into elements of research programs. The following remarks are therefore
preliminary and tentative in nature.
The conference has presented conclusions and recommendations on two levels. The first level
is that of the direct effects of precipitation management on rain, snow, and snowpack; and the
spread of these effects, by processes that are more or less well understood, through the complex
webs of life within the ecosystems involved. Here we have our work cut out for us and the road is
reasonably clearly marked. The issues on this level are suitable for incorporation more or less
directly into the Skywater Program, to be undertaken as priority and opportunity indicate.
The universal need, affecting all environmental impact assessments, is for more precise
expectation of just what changes precipitation management may bring about in the distribution
of precipitation in space and time, and in certain other important parameters of the precipitation
such as its duration and intensity. These objectives are inseparable from the main experimental
investigations of Project Skywater and do not constitute a separate environmental task. However,
a peculiarly environmentally oriented extension of this task may be identified. It is the
application of the experimental results to construction of a stochastic climatology describing
changes in the magnitude and frequency of occurrence of meteorological events of environmental
significance under a regime of precipitation management. The conference results highlighted the
importance of finding out whether seeding for snowpack augmentation at high altitudes affects
the precipitation at lower altitudes. It also identified the importance of determining the nature
and magnitude of offsite changes in precipitation, especially downwind of the primary
operational area.
In areas of snowpack augmentation, the most important link with the vegetational
environment has been pinpointed as the duration of snow cover. This factor has great variability
in both space and time, from place to place on a very fine scale, and from time to time on an
annual scale. Furthermore, snow cover duration is affected greatly by weather events that occur
after the precipitation-management season has ended, especially post-season snowfalls and
rainfalls and amounts of cloudiness and wind. It is affected to a lesser extent by in-season
weather variables that are independent of precipitation management such as the stratigraphy of
the snow resulting from a particular sequence of storm accumulations and redistribution of the
snow by wind. It appears feasible to model the melting of snow cover up to the time of its
disappearance in terms of mass and energy fluxes, and to verify the model's adequacy by
comparison with observations at a few representative sites. It would then be possible to calculate
the durations of snow cover, with and without snowpack augmentation, for a wide variety of
sites and for a wide variety of stochastically generated snowmelt seasons, thus generating an
expectation for the main statistical parameters of snow duration and the dependence of them on
snowpack augmentation.
. The aspects of vegetational gradients that can be associated directly with gradients in
precipitatron amount or snow cover duration are likewise approachable within the Sky water
context. The Uinta Ecology Program, begun last year under contract with the Utah Department
of Conservation and Natural Resources and Brigham Young University, and the studies being
pursued for Skywater by the Pacific Southwest Regional Forest and Range Experiment Station

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