Evaluation of Hail Suppression Effortsby
Atmospheric Water Management Standards Committee
The rationale for conducting project evaluations is to find out how successful the operations are in achieving the desired results. This assessment is more easily said than done. It is impossible to unequivocally determine the effects of seeding on the hailfall from a single convective cell. However, hail suppression projects can be justified if seeding produces a tendency toward reduced damage. Statistical evaluations are intended to identify and quantify such tendencies, but physical measurements of the clouds and precipitation also are desirable. The statistical evaluation of any program can be strengthened by such physical measurements, so that a physical basis (explanation) of the observed effects can be established. In some projects, the sponsors have funded the deployment of a seeding aircraft equipped with microphysical instrumentation to make measurements before and after treatment. These measurements provide physical evidence of how seeding alters the cloud microstructure (Sánchez et al. 1998; Krauss 1999). Although these measurements are not made of every treated cloud, sponsors gain confidence in the seeding system, and scientists evaluating the program get some direct physical measurements of cloud characteristics and responses to treatment. In this chapter, some of the available means for evaluation are presented. All project sponsors are strongly urged to include some evaluation procedures in their program design.
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