Title: Below Average Rainfall Prompts New Look At Precipitation Enhancement
Full Citation
Permanent Link: http://ufdc.ufl.edu/WL00002532/00001
 Material Information
Title: Below Average Rainfall Prompts New Look At Precipitation Enhancement
Physical Description: Book
Language: English
Publisher: The Cross Section
Spatial Coverage: North America -- United States of America -- Florida
Abstract: Below Average Rainfall Prompts New Look At Precipitation Enhancement, Jan 1995
General Note: Box 10, Folder 22 ( SF Water Modification - 1981-83 ), Item 2
Funding: Digitized by the Legal Technology Institute in the Levin College of Law at the University of Florida.
 Record Information
Bibliographic ID: WL00002532
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.

Full Text

Below-average rainfall prompts new look at precipitation enhancement

No one knows when the first per-
son turned from the drought-stricken
land, wiped a sweat-soaked brow,
gazed up at the glaring sun, and
thought, "If only I could make it
rain." Since that time, there have been
numerous attempts at weather modi-
fication in order to encourage clouds
to produce more rainfall.
"It is certain that drought will
occur and reoccur in West Texas. This
gives us reason to consider again the
amount of available fresh water that
West Texans can tap; and with cli-
mate changes and the threat of drier
weather, we're going to need to
explore new, different ways of using
the water we have, as well as develop
additional fresh water resources,"
S says George W. Bomar, Senior
*i Technical Specialist, Water Planning
S And Assessment Division of the
S Texas Natural Resource Conservation
Commission (TNRCC) in Austin.
Bomar has assisted the TNRCC in the
regulation of weather modification
activities in West Texas during the
past 20 years.
Weather modification is the at-
tempt to change or control natural
development of precipitation cloud
forms in the lower half of the earth's
S atmosphere.
The typical large cumulus clouds
S that form in the High Plains area
have relatively few natural nuclei
(such as salt particles, sand particles,
or specks of dust) around which
moisture in the air can coalesce, or
grow together, to become raindrops.
Bomar says that this lack of nuclei
means that most of the cloud mois-
ture is never converted to raindrops.
S"Cloud seeding is designed to
increase the number of nuclei. You
want to cause five to ten times as
many tiny raindrops or water
droplets to form, which will then
interact with other droplets, colliding
, and coalescing to form larger and

larger raindrops," he says.
Silver Iodide (Agl) is the most
popular cloud seeding agent used
today, because it very closely approx-
imates natural ice crystals.
"By introducing silver iodide
through cloud seeding, you hope to
transform enough of the cloud mois-
ture into water droplets to generate
enough large raindrops to survive the
fall through the dry subcloud layer
and reach the surface as meaningful
He added that as cloud water is
transformed into water droplets,
the additional heat generated caus-
es the cloud to grow taller. As the
cloud system grows taller, its
updraft strengthens and imports

more moist air from the surface.
"The cloud system then becomes
more efficient. It will grow taller, last
longer, pull in more moist air, and
transform that air into more moisture
droplets," he says.
As the rainfall load increases, it
sinks in the cloud, overcomes the
updraft, and falls out of the cloud as
a rain shield, bringing with it a very
cold downdraft.
This, in turn, causes additional up-
drafts, which help create extra cloud
growth on the periphery of the sys-
tem. The resulting feeder cells on
each side of the thunderstorm can
cause rain to fall over a greater area,
may result in a longer life for the
storm system, and may cause more

26- 2

24.01 24.04
S224 99 23.12
ST \I \2239
o 22-4 0.0
= 20.82 1f *0

SA EP A (18.55 In 6 &U

13.7 1312 75
1 1 -

1974 1979 1984' 1989 1994
Lubbock received below-average precipitation during 10 of the 20
years shown on this line graph. Historical average precipitation for the
Lubbock area (1911-1994) is 18.55 inches.

rainfall to be produced.
Weather modification projects do
not increase rain in one area at anoth-
er area's expense. Bomar says clouds
are inefficient since they do not gath-
er and release all the moisture that is
available. Clouds only contain an
average of one percent of the total
atmospheric moisture at any time. If
cloud seeding doubled the efficiency
of a cloud formation, it would likely
only contain two percent of the avail-
able moisture-leaving 98 percent
available for other uses.
The Colorado River Municipal
Water District at Big Spring
(CRMWD) has operated a cloud seed-
ing program since 1971. The cloud
seeding project is conducted from
April to October in order to augment
rainfall runoff into the District's
reservoirs and increase water sup-
plies for irrigation purposes.
According to CRMWD officials,
the cloud seeding has increased aver-
age annual rainfall by 30 to 40 per-
cent (4 inches) in its target area.
The CRMWD, in conjunction with
the Plains Cotton Growers Associa-
tion, has been studying the effects of
weather modification on dryland cot-
ton yields in the target areas. Results
show that dryland cotton yields from
1970-1988 increased by 46 percent in
Borden, Scurry, Howard, and
Mitchell Counties after the cloud
seeding program began.
Additional information about pre-
cipitation enhancement is available
by contacting George W. Bomar,
Senior Technical Specialist, Water
Planning and Assessment Division,
Texas Natural Resource Conservation
Commission, PO Box 13087, Austin,
Texas 78711-3087, or by calling (512)

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January 1995

Page 4


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