Title: Cloud Seeding In Utah
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Permanent Link: http://ufdc.ufl.edu/WL00002541/00001
 Material Information
Title: Cloud Seeding In Utah
Physical Description: Book
Language: English
Publisher: NAWC
 Subjects
Spatial Coverage: North America -- United States of America -- Florida
 Notes
Abstract: Cloud Seeding In Utah
General Note: Box 10, Folder 22 ( SF Water Modification - 1981-83 ), Item 11
Funding: Digitized by the Legal Technology Institute in the Levin College of Law at the University of Florida.
 Record Information
Bibliographic ID: WL00002541
Volume ID: VID00001
Source Institution: Levin College of Law, University of Florida
Holding Location: Levin College of Law, University of Florida
Rights Management: All rights reserved by the source institution and holding location.

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^;" T., 1. WHAT IS CLOUD SEEDING
S.iAND WHAT HAS IT BEEN
.. .USED FOR?

'CLOUD Cloud seeding is the intention-
e E DuN -- al treatment of individual clouds or
S SEEDING storm systems to produce a benefi-
IN UTAH : cial effect. The basic principles
of cloud seeding were established
in 1946. Since that time numerous
~ .. research programs and operational
projects have shown its applicabi-
. -4 lity for many purposes, including
rainfall enhancement, hail suppres-
sion, fog dispersion, as well as
snowpack augmentation.

2. WHAT ARE THE PRINCIPLES
OF CLOUD SEEDING FOR
SNOWFALL ENHANCEMENT?
Clouds are composed of tiny
droplets of water. Although water
., normally freezes at 32oF, cloud
droplets are so small and relative-
S:* I ly free of impurities, they can re-
al.* main in the liquid state at much
S1colder temperatures. At least some
of these droplets must freeze in
order to form snow. Since these
droplets freeze upon impurities in
the atmosphere which are more plen-
tiful at colder temperatures, this
-_ ice-forming process may be enhanced
; -by introducing additional impuri-
:. ties, or seeding agents, to the
warmer portions of the cloud which
are below freezing. Particles of
silver iodide are typically used
as these seeding agents.




.1 I I i I


3. ARE ALL CLOUDS SEEDABLE?


Cloud seeding is simply the
stimulation of natural precipita-
tion producing processes, similar
to applying fertilizer to a field
to stimulate the natural crop grow-
ing process. In Utah, the majority
of the precipitation occurs during
the winter storms as snow. Some
storms (or portions of storms) do
not require seeding because they
contain enough natural impurities
to make them effective snowfall
producers on their own. Conversely,
very small clouds usually associated
with fair weather are not seedable
because they are typically incapable
of producing measurable precipita-
tion under any conditions. It is
the storm systems between these
extremes that can be effectively
seeded for snowfall enhancement.

4. WHAT HAPPENS ONCE. A
CLOUD IS SEEDED?
Tiny silver iodide particles
(released either from ground gener-
ators or aircraft) or dry ice (re-
leased from aircraft) transform
many of the cold cloud droplets
into ice crystals. The ice crystals
attract moisture from surrounding
droplets and grow large enough to
fall to the ground as snow. The
diagrams in Figure 1 illustrate how
a winter storm system can induce
more precipitation to fall out of
certain clouds.


5. WHAT EVIDENCE IS THERE
THAT CLOUD SEEDING
WORKS?

Since cloud seeding is only
feasible when there are clouds pre-
sent and usually only when the
clouds are near to or are already
producing precipitation naturally,
it is natural to ask whether the
seeding increased (or decreased)
the precipitation that was observed
and, if so, by how much.

This question has been address-
ed in research seeding programs in
the United States and elsewhere to
determine when seeding is effective.
Results from a number of research
programs have established that seed-
ing the right kind of storms is an
effective means of increasing pre-
cipitation. Historically, the most
significant seeding results have
been observed in wintertime seeding
programs in mountainous areas. The
apparent differences due to seeding
are on the order of a 10-20% sea-
sonal increase.

6. WHAT EVIDENCE IS THERE
THAT CLOUD SEEDING HAS
BEEN EFFECTIVE IN UTAH?
NAWC has conducted an operation-
al cloud seeding program in Utah
during a majority of the winter
months since January 1974. The in-
tent of this program has been to in-
crease winter snowfall over the
higher yield watersheds of central
and southern Utah.


<1.3/




__L 1 6 H .1 4 1 .1 I ,W I IW I- I ,I I J I k N L I


This project was not designed
to be a research program, and it is
therefore difficult to determine the
effects of seeding. However, it is
possible to estimate these seeding
effects by comparing the amount of
precipitation that fell in the seed-
ed area to that which fell in a
nearby unseeded area. The western
part of the state was designated
the "unseeded" control area. A
third area, east of the major moun-
tain barrier was designated the
"eastern downwind area". Historical
precipitation data for the period
from 1956 through 1973 (before any
seeding) were compiled for each of
these areas for the months of
January, February, and March. This
three-month period was consistently


NATURAL MOUNTAIN CLOUD
(Top temperature 140 to -22 F)


seeded each year during the 1974-78
period. Using this information, it
was possible to predict the amount
of expected precipitation in the
target area during the seeding pro-
gram based upon the amount observed
in the control area.
Results of this analysis indi-
cated four of the five seeded years
received greater precipitation in
the target area than was predicted.
An overall increase of about 18% was
indicated for the five years. The
odds of an increase this big occurr-
ing naturally are approximately one
infifty. These results compare
favorably with results obtained in
other winter seeding programs. Fig-
ure 2 graphically portrays these
results for each seeded year and the
five years combined.


SEEDED MOUNTAIN CLOUD
(Top Temperature 140to -22 F)


15 to 50 minutes required
for snow crystals to grow
and fall out


SILVER
IODIDE
Relatively few snow crystals form and GENERATOR Many snow crystals form in seeded
fall out. Most cloud water remains aloft clouds, thus depositing most of the
in the form of tiny supercooled droplets cloud water on the ground
Figure 1


II


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43--"




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Figure 2
Comparison of Seeded Years' Actual
Precipitation with Predicted Precipitation
for the January March Period.
"x- x'78
S10 -
C
Z
0 8
F 1974-78 7,

76
u 4 -
EL '77
-J
< 2


2 4 6 8 10
CALCULATED PRECIPITATION
(inches)
Note: Years above the slanted solid line
received more precipitation than
predicted. The 1974-78 average is
18% greater than predicted,

7. IS CLOUD SEEDING
LIKELY TO TAKE WATER
AWAY FROM SOME OTHER
AREA?

Recently, a group of leading
scientists met at a workshop con-
ducted by the National Science
Foundation to examine this problem.
In general, their conclusions were
that seeding effects in the area
"downwind" from a seeded target tend
to be of the same sign (increases
or decreases) and roughly of the
same magnitude as those observed in
the target area.


In the case of Utah, these con-
clusions are supported since it
appears that the "downwind" area
in east-central Utah received about
25% more precipitation than would
be predicted on the basis of the
control area precipitation during
S the five seeded years. This in-
crease would be expected to happen
S by chance in less than one case
in ten. There is currently little
evidence available to support the
"Robbing Peter to pay Paul" con-
cept that seeding in one area will
deprive some other area of its nor-
mal rainfall.

8. ARE THERE ANY NEGATIVE
ENVIRONMENTAL EFFECTS
FROM SEEDING CLOUDS?
No. The possibility of nega-
tive environmental impacts tox-
icity of seeding material, or
creation of severe weather condi-
tions, such as hail storms and
floods, have been considered and
studied extensively in several gov-
ernment research programs. All
evidence collected thus far, indi-
cates that there are no negative
environmental effects from seeding
clouds, provided the programs are
conducted properly by knowledgeable
organizations.

9. WHO ARE NORTH AMERICAN
WEATHER CONSULTANTS?
Since 1950, North American Wea-
ther Consultants has been a leader
in research and practical applica-







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tion of the new science of weather
modification. The firm has con-
ducted over 200 project seasons of
cloud seeding, to increase water
supplies throughout the United
States as well as several foreign
countries. Boasting the largest
permanent staff of commercial wea-
ther modification experts in the
world, North American leather Con-
sultants has been cond acting the
Utah Cloud Seeding Project since
its inception in 1973. The firm
maintains permanent offices in both
Utah and California.
10. HOW DOES UTAH BENEFIT
FROM CLOUD SEEDING?
Utah, which ranks as the second
driest state in the nation, relies
heavily upon snowpack from the
winter season to replenish its water
supply. Fortunately, the winter
storms which sweep into the state
from the Pacific Ocean are prime
candidates for precipitation aug-
mentation through cloud seeding.
The use of this technology as an
integral part of a total water re-
sources management program promises
to provide additional benefits to
all the residents of Utah at a rel-
atively small cost (estimates of
cost vary from $1-$10 per acre-foot
of additional water produced).
These increases in water supply may
be obtained without large time and
capital outlays necessary to build
new dams or diversion systems and
may be targeted to affect those
areas where existing storage and
distribution facilities have not
reached normal capacity.




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