WMOD00546

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

affected more by the number of seasons it must run than the number of preci pi-
tation gages it employs, it would be worthwhile to pursue his suggestion
further by examining the statistical properties of area-depth curve parameters.

An examination of Table 5 reveals other possibilities. Since the values of
the coefficient of variation (log-normal standard deviation for log-normally
distributed variables) for stonn area and storm duration are considerably
less than that for storm rainfall volume, a substantially smaller sample size
will be required to detect an equivalent seeding effect if the evaluation of
the experiment were based on thl~se storm characteri stics. Increases in the
values of both parameters have been postulated as a result of seeding for
dynamic effects (Simpson, 1980) which is thought to induce the merger of
neighboring storms and/or sustain the propogation of the storm by l~ncouragi ng
the development of additi onal rj~incell s.

8. Summary

Estimates of precipitation volume from precipitation gage networks are
subject to a component of variability that is caused by the random direction
of movement and orientation of the storm and the variations in storm structure.
A computer model of raincell isohyetal patterns has been used to assess
quant itative ly the sampl i ng var'j ,ance of gage networks. We have shown that
the coefficient of variation increases with decreasing gage density and
increasing precipitation gradient. Contrary to the sampling error studies of
other investigators, it was found that the mean precipitation remained
constant as the gage density dec:'reased but its standard deviation iincreased.

The theoretical isohyetal pattey'ns were then related to observed isohyetal
maps and the characteristics of their structure. The observations suggested

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