WMOD00546

• Project Name: High Plains Cooperative Program
• Title: On the Sampling Variance of Raingage Networks
• Weather Modification - Doc Type: Report

a tendency for the precipitation gradient to be steepest, increasing rapidly
toway'd the storm preci pitation maximum, in short-duration convective storms
of small areal extent. More uniiform precipitation gradients tend to be found
in steady-type rains and large, long-lasting storms. Expressed in terms of
the percentage of storm area containing 50 percent of the preci pitation
volume, the precipitation gradiE!nt was found to vary from 15 to 30 percent.
It was also found that convective raincell patterns tend to be elliptical in
shape.

Finally, the relative importance' of sampling variance and natural storm
preci pitat i on va ri abi 1 ity was ex.ami ned in connect i on with the eva 1 uati on
of precipitation augmentation ex.periments. The sample sizes required to
evaluate such experiments due to sampling variance alone can be appreciable;
however, for reasonable gage densities, it only contributes about 10 percent
to the total sample size requirement. Methods of obtaining reductions in
sample precipitation variability through the use of covariates will have to
be found before the use of high,~r gage network densities is warranted.

Acknowledgments

The authors wi sh to thank John 11i ddl eton and Robert Pritchard for thei r
assistance in obtaining the radar precipitation characteristics of Montana
convective storms and their statistical properties. The authors al~e also
indebted to Dr. K. Ruben Gabriel whose critical comments and constructive
suggestions led to significant 'improvements in the clarity and quality of
this paper.

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