WMOD00545

• Project Name: Colorado River Basin Pilot Project
• Title: Test of Runoff Increase Due to Precipitation Management for the Colorado River Basin Pilot Project
• Date: 3/3/1973
• Weather Modification - Doc Type: Report

327

JOURNAL OF APPLIED METEOROLOGY

440

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VOLUME 12

400

It:'

360

320

,., Seeded Season
. Unseeded Season

280

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":9

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19,6 1953
1967.. 1950 ~961
1955 .1939
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\1963
Target: Son Juan River ot Pagosa Springs, Colorado
Control: Lake Fork at Gatevlew, Colorado
RegreSSion Line Bo,sed on 27 Years of Record '
Significance Level: 95% (one~tailed lest)
Apparent Relatll/e Increose: 27 %
Apporent Mean Seasonal Increase: 58.000 acre-ft.

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00 80 120 160 200 240 280 320
Conlrol Seasonal (April - August) Flow in Thousands ot Acre - Feet

FIG. 3. Regression line between target seasonal runoff
and control seasonal runoff.

target control LV. but a global pair, i.e., total target
runoff and total control runoff. That it works is demon-
strated by an analysis of the effect of weather modifica-
tion on nmoff in the Wolf Creek Pass area. Under
sponsorship of the State of Colorado and the direction of
Prof. Grant of Colorado State University, the area was
seeded during the years 1965, 1967 and 1969. The
target-control conditional Student's t-test was applied
to several pairs of target-control LV. and to the global
paiL The results are displayed graphically in Figs. 3-9.
For the global pair (Fig. 9) an apparent relative increase
of 20% is shown to be significant at the 99% (one-
tailed) or 98% (two-tailed) level, the highest signif-
icance level shown in all the figures, whereas for an
apparent relative increase of 27% (Fig. 3) the signif-
icance level is only 95% (one-tailed) or 90% (two-
tailed). Note that in Prof. Grant's experiments all
seedable storms were seeded. In the Colorado River
Basin Pilot Project they will not be. Had the global
apparent increase been only 10%, given the hydrologic
characteristics of the watersheds involved, the signif-
icance level attained in three years of experiments
would have been less than 95%. Nevertheless the
results are encouraging.
Clearly the global (or total) target runoff is a partic-
ular linear combination of the elemental (or component)
target runoffs, i.e., a combination where all the weights
in the combination equal unity. This remark suggests
an additional possibility of minimizing N by considering

II