WMOD00294

• Project Name: Project Skywater - Sierra Cooperative Pilot Project
• Title: The Design of SCPP-1 - A Randomized Precipitation Augmentation Experiment on Winter Cellular Convection in the Central Sierra Nevada
• Date: 11/1/1983
• State: NV
• Weather Modification - Doc Type: Report

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I. INTRODUCTION

The mission of Project SKYWATER, the Bureau of Reclamation's precipitation
management research program, is to develop a practical, scientifically sound,
and socially acceptable technology of cloud seeding for enhancing the
Nation's supply of clean water. This mission is pursued in part in the SCPP
(Sierra Cooperative Pilot Project), a winter cloud seeding research effort in
the central Sierra Nevada. The SCPP is conducted by the Bureau in coopera-
tion with the States of California and Nevada, local agencies, and the
public.

The major objectives of the SCPP are to identify the conditions under
which seeding winter clouds in a prescribed manner leads to precipitation
increases, precipitation decreases, or no effect, and to learn how much water
may be produced if increases result. Also, the area and magnitude of the
effects, including environmental, social, and economic responses, are to be
determined.

This document describes a revised design of SCPP-1, the first in a series of
exploratory experiments planned during the SCPP. SCPP-1 began during the
wi nter of 1982-83, a year of record snowpack. Because of prolonged suspen-
sions, only one experimental unit was collected, along with one deliberate
seeding experiment. Analysis during the past year has led to a significant
rethinking of our ideas about SCPP-1 including the physical hypotheses, the
~ treatment, and evaluation design mechanisms.

This document updates the current thinking and documents our current knowl-
edge on the study of convective cloud types by SCPP scientists over the past
7 years. It is believed that this type of experiment on the selection
and treatment of initially nonprecipitating convective cloud elements may
provide the clearest evidence or incl ination of a treatment effect as an
exploratory experiment is designed to do (Flueck, 1982). The proposed new
design is felt to be more consistent in both the conceptual model proposed
and in the prospects of reaching a more scientifically plausible and statis-
tically credible experiment.

Increases in runoff expected from the treatment of SCPP-1 cloud types are now
expected to fall short of the originally proposed 5 percent. This is due to
the anticipated reduction in the number of experimental units available for
selection each season as well as the limited area and reduced time of the
treatment effect for these initially nonprecipitating convective cloud
types. Thus the anticipated benefit cost ratio, assuming operational seeding
by water users, would fall below the 3.5:1 value shown in table 11-1 for a
2.5 percent increase.

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Again we would state, however, that the biggest benefit from such an explora-
tory experiment will be in developing the technology and the understanding
that will help treat and evaluate other, more potentially significant convec-
tive as well as nonconvective cloud types that would show a more substantial
benefit-to-cost ratio from cloud seeding.

In this vein, work is continuing on designing future exploratory experiments
on more complex and/or extensive cloud systems (SCPP-2). This might include

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