WMOD00517

• Title: On the Use of Homoclimes for Estimating Environmental Effects of Precipitation Management
• Date: 8/2/1976
• Weather Modification - Doc Type: Report

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through the course of natural precipitation variations similar to those expected to result
from the precipitation management. Figure 3 shows that nature has herself repeatedly per-
formed the experiment of increasing or decreasing the two-year precipitation by amounts

15

I .
... / W DODGE CITY, KANSAS
/. . 2 - YR. RUNNING MEA NS OF
14 . ANNUAL AVERAGES
cr I 1875 - 1960
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II
200 300 400 500 600 700 800

PRECIPITATION. mm

Fig. 3 - Two-year running means of precipitation and temperature, Dodge City, Kansas,
1875-1960

exceeding the expected capability of precipitation management. The short-term consequences
are there to be observed and assessed. Several studies so far accomplished, such as those
of RogIer and !Iaas (1947) and Ilausle (1972), show that additional growing-season precipita-
tion results in increased growth and vigor of nearly all grasses, forbs, and shrubs, and of
some trees. Other trees, especially those on sites where minimum moisture needs are met,
lre relativel)' insensitive. Rate of decomposition is increased, as is rate of weathering
of parent soil material and release of mineral nutrients, but also the rate of leaching.
The larger, longer-lived animals likewise tend to thrive in wet years. There are marked
population changes among some annual plants and some small mammals. For agricultural crops,
moisture early in the growing season is generally more important than during the maturing
phase. Further research, with emphasis on consistency of approach and methods, would serve
to quantify the effects further.

Respecting middle-term variations, those spanning 10 years, the idioclime is still the best
homoclime even though there are fewer situations for which adequate data are available.
Figure 4 shows that Dodge City, Kansas, lias experienced several successive or nearly succes-
,sive decades the second of which had substantially more precipitation than the first. The
possibilities for studying the environmental changes that accompanied these episodes have
not been well exploited, and the opportunity for doing so appears to hold promise. From
relatively scanty observations, such as those of the Medicine Bow ecology program, certain
tentative conclusions can nevertheless be dralm. The increased growth and vigor noted for
short-term precipitation increases is sustained at the middle term, accompanied by a dis-
tinct change in species composition among annuals and fast-maturing perennials. In semi-
arid Climates, the percentage of soil covered by vegetation increases significantly after