WMOD00570

• Title: Precipitation Enhancement Effects of Sorghum, Using a Daily Growth Model
• Date: 4/1/1982
• Weather Modification - Doc Type: Report

assumed that the number of days that rain could be induced from nonpre-
cipitating clouds is approximated by one-third of the number of trace
days. Scenario 5A assigns 3 mm of rain to every third trace day, starting
with the first one. Scenario 58 assigns 6 mm to every third trace day.
In Scenario 5C, 3 mm are assigned to each of the first two of every three
trace days. This provides the same amount of additional precipitation as
Scenario 58, but increases the frequency with which the water is applied.

6. Scenario
variant of a
Huff (1971).
alone rather

6. - Is a combination of Scenarios lA, 2A, and 3A. It is a
precipitation enhancement scenario suggested by Changnon and
In the scenario used, rains greater than 25.40 mm are left
than decreased.

7. Scenario 7. - Is a combination of Scenarios 5 and 6; Scenario 7A
comblnes 5A wlth 6; Scenario 78 combines 58 with 6. These represent
situations in which precipitation is increased for most natural events and
induced on some days when rain would not naturally occur.

8. Scenario 8. - Is a combination of Scenarios 18 and 5A, and represents
a situation ln which the smaller natural events are affected and rain is
induced on some days on which precipitation would not naturally occur.

9. Sc~nario 9. - Increases all rains of 25.40 mm or less by 10 percent.
This scenario assumes that all but the largest natural precipitation
events are susceptible to precipitation enhancement.

These scenarios assume that precipitation enhancement activities will
have no effect on either temperature or solar radiation. While we realize
that additional precipitation and subsequent evaporation can affect tempera-
tures and that weather modification may extend the duration of storms,
thereby reducing solar radiation, the primary purpose of this study was to
assess the direct effects of the additional water on yield.

Amount

Natural Conditions. - The Spearman rank correlation method (Siegal, 1956)
was used to test quantitatively the relationships between yield and amount
of precipitation for the total period and for the various stages of plant
growth and development. At the two Texas sites, the correlation between
total precipitation and yield is greater than 0.90 (table 3). The correla-
tion is moderate at Goodland and low (not statistically significant) for both
Oklahoma City and Concordia. The correlations between yield and growing- ~
season precipitation were lower than those for total precipitation at
Goodland, Lubbock, and San Angelo, suggesting the value of pregrowing-season
precipitation. The growing-season correlations at Concordia and Oklahoma
City are higher than the total-precipitation correlations, but.only Oklahoma
City's is significant.

Linear regression techniques were also used to explore the relationship
between total precipitation and yield. Figure 1 shows the regression line
for Lubbock and the scatter of the data points. Figure 2 shows the regres-
sion lines and coefficients of variation for all five sites; the data points
were omitted to reduce clutter. All sites indicate that the greater the

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