Repeatability of Strong Responses in Precipitation Management

Reported evaluations of 49 cloud-seeding projects, 35 of them randomized, yielded nearly 80 data sets categorized according to expected responses based on cloud-physics concepts. The median response in the 31 sets of cumulus congestus with tops between -10 C and -20 C was + 90%, all increases except one nil; the median response of 11 sets of cumulonimbus with tops colder than -35 C was -30%, all decreases except one nil. Other sets were smaller and mostly less consistent. Hypothetical explanations are offered, and it is concluded that, even without full theoretical understanding, cloud seeders are able to achieve consistent results in the field.