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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a wet decade and there may be some invasion of the habitat by more moisture-loving plant
varieties. Populations of most animals also tend to increase in a wet decade.

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PRECIPITATION, mm

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Fig. 4 - Ten-year running means of precipitation and temperature, Dodge City, Kansas,
1875-1960

4. Homoc1imes for Long-term Variations in Precipitation

Respecting the effect of precipitation changes lasting much longer than 10 years, the idio-
clime is no longer the best homoclime for the altered environment. Although large long-term
precipitation variations have doubtless occurred, few records of precipi.tation and fewer of
environmental parameters go back more than two centuries. One must look for a geograph-
ically separated homoclime.

In the midwestern United States, where the isohyets run nearly normal to the isotherms
(Fig. 5) a journey of only 60 km eastward along an isotherm brings an increase of 10 percent
in precipitation. In a dense raingage network in Illinois, there is an example of a
12-percent difference in IO-year mean precipitation over a distance of only 8 km, due