CLOUD SEEDING IN THE AMERICAN TROPICS 
[o) 
A Florida 
a) TARGET AREAS 
AND 
metS 
RAIN GAGES 
Soke oumMaslON = 204 mis0 
> = Scale of kilometers 
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Fra. 1—Map showing rainfall stimulation tar- 
get areas and rain-gage locations in central and 
southern Camagiiey Province, Cuba 
a 15% increase in rainfall. In February and 
March of 1954, experiments were conducted on 
the spray seeding of warm clouds, but operations 
were suspended because of adequate field mois- 
ture. They were not resumed again until May of 
1956, because of sugar marketing and milling 
restrictions, but have been conducted much of 
the time since then. Operations were somewhat 
upset by local political disturbances late in 1958, 
and some of the generators were put to uses 
other than those intended by the sugar mill, in- 
cluding perhaps some connection with an iso- 
lated dry-season shower that bogged down a 
column of tanks as it was about to close in on a 
large rebel encampment located within the tar- 
get. Perhaps some future historian will be able 
to tell us if this was the first direct use of cloud 
seeding to discomfit an enemy. 
There were several rain gages located in vari- 
ous sections of the Francisco property, and the 
adjacent properties also each had several rain 
gages. It was therefore possible to assemble a 
considerable network of gages, as shown on Fig- 
ure 1, with at least ten years of record, 1941- 
1950, before the start of seeding. The first at- 
413 
tempt at an evaluation was made after the 1951 
season by comparing the percentage of normal 
rainfall received during the operating period on 
the target with the percentage normal received 
on the surrounding plantations, and it was esti- 
mated that an merease of 26% had been achieved. 
After the longer operations of 1952 over both 
Francisco and some adjacent plantations, the 
evaluation was improved by using a regression 
analysis using the seasonal total rainfalls for the 
operated portion of the year for each year of the 
historical record. This evaluation indicated an 
increase of 28% with significance for the group 
of operations well beyond the one per cent level. 
By this time we had thoroughly scoured the 
countryside for rain gages, and from then on the 
composition of the control data was not changed 
except to drop the Lugareno gages—located un- 
der the cartouche of Figure 1—when it was found 
that they had no useful degree of correlation 
with the target. The evaluation of later years, 
however, was further refined by basing the re- 
gression on individual monthly rainfall totals 
instead of seasonal, and by transforming them 
to normality. The two evaluations made subse- 
quently have shown respectively 15% and 25% 
increases. Figure 2 shows the regression with the 
results of the 1956 operations. The probabilities 
of chance occurrence are arrived at by a one- 
tailed t-test, allowing for the size of the sample 
and the departure of the control variable from 
its mean. Where several months of operation of 
a project have been tested against a single re- 
gression, the t-tests have been combined into one. 
Seeding of warm clouds has been carried out, 
30F Correlation coefficient r= .92 
- 20 Probable error of r f= .029 
3 15 r/f = 32 
= 
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ihe 
a 5 
°o 
a8 
cz 
x2 | 
o> 
ol 
5= j *unseeded month 
Lge gs © seeded month 
" 
Wk (e) 
" fo) | | 5 10 15 20 30 
> 
X=x3 = Control zone monthly rainfall, 
May to November 
Fic. 2—Regression diagram illus- 
trating the results of cloud seeding at 
Francisco, Cuba, May to November, 
1956 
