WMOD00570

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

Table 2 presents the mean precipitation for the study period, the mean and
median simulated natural yields for each of the five sites, plus the mean
normalized yields for the stress-relieved conditions and the percent of years
each stress was daninant. Water stress was domi nant almost every year at
Lubbock and was dominant most years at San Angelo and Oklahoma City. Tempera-
ture stress was more frequent than water stress at the Kansas sites, but, in
the mean, water stress had an equal or greater impact on yield. For most
years at all sites, no-water-stress yields exceeded simulated natural yields,
suggesting that additional precipitation could have increased production. At
the Kansas and Oklahoma sites, however, the increase was sometimes quite
small. Tables presenting results are found in appendix A.

EFFECTS OF AMOUNT AND TIMING OF PRECIPITATION ON YIELD

To examine the effects of amount and timing of additional precipitation, two
approaches were employed. Fi rst, the model-s imul ated result s for natur al
conditions were analyzed for all years at all five sites (129 years total).
We looked at natural conditions because the observed year-to-year variations
in precipitation characteristics should provide considerable insight into the
general effects of timing and amount (both total and per event). Precipita-
tion enhancement technology, however, may be more effective over some ranges
of natural precipitation characteristics than others. Therefore, nine types
of precipitation enhancement scenarios were used to modify the natural
precipitation characteristics at all sites for all years. Inclusion of these
scenarios is not meant to imply that all (or any) of them are feasible.
They are used-only to simulate the ranges of effect that weather modification
might achieve.

1. Scenario 1. - Assumes that moderate and large rain events are naturally
efficient, but small events can be strongly influenced. Scenario 1A
increases rains between 0.25 and 2.54 mm by 75 percent. Scenario 1B
increases these rains by 150 percent:

2. Scenario 2. - Assumes that moderate rains can be influenced but small
and large rain events are not affected. The scenario increases rains
between 2.55 and 12.70 mm by 30 percent.

3. Scenario 3. - Assumes that only large rains (those between 12.71 and
25.40 mm) can be influenced. Scenario 3A increases these rains by
10 percent. Scenario 3B increases them by 20 percent.

4. Scenario 4. - Increases only preplanting precipitation of 25.40 mm or
less to assess the effect of increasing soil water prior to planting.
Scenario 4A increases these events by 10 percent. Scenario 4B increases
them by 50 percent.

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5. Scenario 5. - Assumes that all natural rain events are efficient but
that precipitation can be induced on some days when rain would not naturally
occur. Days with a trace of precipitation were chosen as surrogates
because no data were readily available by which nonprecipitating days
suitable for weather modification could be identified. It was arbitrarily

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