WMOD00438

• Title: HIPLEX: A Cooperative Program on Rain Augmentation in the High Plains
• Date: 6/1/1984
• Weather Modification - Doc Type: Report

presence of large numbers of supercooled drops.
along with the lack of ice in the updrafts. suggests
ice-phase seeding as having a potential to affect the
precipitation process.

As noted above. the ice-phase precipitation proc-
esses in the later stages of cloud lifetime appear to
be relatively efficient. while the coalescence process
appears to dominate the early stages to cloud devel-
opment. especially at low levels. Takeuchi (1980)
therefore concluded that a greater potential for ice-
phase seeding lies in the treatment of smaller clouds
at a time prior to major precipitation development.
The duration of the seeding window was estimated
at about 1 3 minutes before the cloud evaporated or
became filled with natural ice particles. In order to
take advantage of the adequate liquid water content
(1 gm-3) and low ice particle concentration
k 1 0 L-l) during this brief seeding window. Takeu-
chi recommended seeding the clouds from above
with droppable agents rather than cloud base
seeding.

In order to have seeding targets big enough to pro-
duce substantial showers. Jurica et al. (1981) sug-
gested seeding days when natural echoes would
occur. As natural radar echo tops nearly always
exceeded 8.7 km. they suggested that operations be
conducted on days when airmass structure would
permit clouds to reach at least that height.

Several authors have written about the possibility of
making clouds larger through dynamic seeding
effects. thereby obtaining major rainfall increases.
Since small clusters generate only about 5 percent
of the total convective rainfall. a 20-percent increase
in their rainfall due to seeding would yield a very
small increase in the total rainfall (about 1 percent).
However, since large clusters are responsible for
27.5 percent of the total rainfall. Jurica et al. (1980)
concluded that if small clusters could be induced to
develop into large clusters. then the increase in rain-
fall through cloud seeding would be substantial. Con-
sequently. the study suggests that "Further
investigation should be directed toward discerning
the feasibility of inducing small clusters to intensify
into large clusters."

Discussion of the above suggestions and of other
possibilities for modifying convective clouds to
increase rainfall in Texas is deferred to section 6. fol-
lowing a presentation of HIPLEX findings from Kan-
sas and Montana.

3.7 Economic Studies

Support for HIPLEX on the part of the State of Texas
was based on the realization that Texas has long-term
water problems and that rain augmentation by cloud
seeding is one possible. but partial. solution to those

problems. Major needs exist for municipal water and
for water to satisfy the demand created by irrigated
crops. such as cotton, and by oil well extraction
techniques.

In west Texas, the Ogallala aquifer, a major source
of municipal and irrigation water. is being exhausted.
It supplies irrigation water for 23900 km2 (5.9 mil-
lion acres); however, at the current rate of draw-
down, it is estimated that only 37 percent of that
land can be supplied by the year 2000 (Riggio et aI.,
1983).

Exploratory studies by Texas DWR of the operational
program that preceded and was colocated with
Texas HIPLEX in the Big Spring area showed that the
net economic benefits of a 10-percent increase in
rainfall due to seeding in a 33 000-km2 (8.1 million
acre) project area would be an overall expansion in
regional output of $ 3.68 million and an expansion
in net regional income of $ 2.3 million.

Additional studies were carried out as part of Texas
HIPLEX. Estimates of the effects of increases of pre-
cipitation on crops and rangeland Wl9re developed
using multiple linear regression techniques. Crop
yields were estimated based on precipitation, tem-
perature. and previous range forage condition. Table
3.3 shows the estimated monthly impact of a
1 O-percent increase in rainfall on re!~ional income
from cotton. grain, sorghum, and wheat crops. In the
Kengla et al. (1979) study, projected increase in
annual growing season precipitation for each county
was calculated and multiplied by each county's aver-
age annual irrigated acreage in years 1971 to 1975
to determine the extent to which additional rainfall
could be expected to replace ground-water pump-
age. The department's economic studies revealed
that the additional rainwater would have the follow-
ing net economic effects on the Big Spring-Snyder
west Texas Region:

a. A reduction in ground-water pumped irrigation
requirements of 28.2 million m3 (22 800 acre-ft)
per year, which would reduce irrigcltion costs by
approximately $547,000 in 1977 dollars and
expand regional personal income by about
$371,000.

b. The additional rainfall in the study area would
expand dryland crop and livestock production,
thereby increasing net farm income by approxi-
mately $1.6 million. Due to economic multiplier
effects, this would eventually expand regional
output by about $3.9 million and regional income
by over $1.9 million.

c. The net effect of the additional rainfall in the
dryland and irrigation crop sectors of the Big

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