WMOD00528

• Title: The Feasibility of Enhancing Streamflow in the Silver Iodide in the Sevier River Basin of Utah bt Seeding Winter Mountain Clouds
• Date: 12/1/1991
• Weather Modification - Doc Type: Report

1. INTRODUCTION

The Bureau of Reclamation (Reclamation) and the Utah DWR (Division of Water Resources) are mutually
interested in detennining the feasibility of enhancing the winter snowpack and subsequent runoff in Utah's
Sevier River Basin shown on figure 1-1. Reclamation investigated the potential of developing a
teclmically sound and validated snowpack enhancement program for the Sevier River Drainage. The
technology of weather modification, commonly called cloud seeding, was to be considered as the means
of snowpack augmentation. Much of the streamflow in the Sevier River is due to the spring and early
summer melting of the mountain snowpack in the basin.

The objectives of this investigation were (1) to detennine the meteorological feasibility of increasing the
water yield of the Sevier River Basin through the application of state-of-the-art winter cloud seeding to
mountain clouds, (2) to develop an experimental design to scientifically validate the effects of cloud
seeding in the basin, and (3) to provide reasonable estimates of the magnitude of the precipitation and
resulting streamflow increases that might be expected from operational seeding, and the benefit/cost ratio
of such application.

Investigations of winter snowpack enhancement by cloud seeding in Utah began in the late 1960's. Early
support of this wotX was provided to Utah State University by Reclamation's Project Skywater. Detailed
analyses of experimental seeding from the winters of 1969-70 through 1975-76 were reported by Hill
(1979).

Since 1981 a research program largely sponsored by NOAA (National Oceanic and Atmospheric
Administration) has investigated the effectiveness of the Utah operational seeding program (Reinking,
1985). This Utah/NOAA Atmospheric Modification Program has investigated the physical processes that
occur in both seeded and nonseeded winter stonns passing over the Tushar Mountains of south central
Utah. A series of comprehensive Final Reports has documented these studies. These reports and
associated publications in the scientific literature, reviewed in section 3, have provided infonnation that
has substantially contributed to this feasibility study.

In addition to reviewing the results of past research efforts in Utah, and similar stUdies from nearby states
in the Rocky Mountain region, this report examined precipitation data from Cedar Breaks, UT. Blowhard
Mountain radar, a site atop Cedar Breaks, provided high altitude data in the Sevier River Drainage with
a reasonably long-tenn record. ObseIVations from this site are assumed to approximate the snowfall
climatology for the higher elevations in the drainage which provide much of the streamflow.

Hydrological modelling studies have been provided by the NWS (National Weather SeIVice) River
Forecast center in Salt Lake City, using estimated increases in precipitation expected from cloud seeding.
From the NWS model results, a detennination of the benefits of cloud seeding was made by DWR
personnel. These estimates, along with probable costs of conducting an operational program, provided
infonnation for a preliminary benefit-cost analysis. However, a number of uncertainties exist in making
the benefit-cost estimates that can only be clarified by more definitive physical and statistical studies than
conducted to date.

The review in section 3 revealed several uncertainties concerning the effectiveness of winter cloud seeding.
Consequently, considerable attention is given to designing a weather modification demonstration program
for the Sevier River Drainage. These uncertainties are not unique to the Sevier Drainage or even to the
State of Utah, but many of them should be answered for the intennountain West in general in order to
place the technology of winter cloud seeding on a tinner scientific footing.