AN EXPLORATORY ANALYSIS OF CROP HAIL INSURANCE DATA FOR EVIDENCE OF CLOUD SEEDING EFFECTS IN NORTH-DAKOTA

The basis for the cloud seeding operations of the North Dakota Cloud M odification Project (NDCMP) is first outlined. Then the multiresponse permutation procedures are applied in an analysis of crop hail insuran ce data for the NDCMP target area and for an upwind control area in ea stern Montana. A historical analysis of the annual hail insurance loss ratios for the target area indicates lower hail-loss experience durin g the NDCMP operational years 1976-88. A corresponding analysis for th e control area shows no indication of a difference during those years, suggesting the absence of any significant climatological variation. A nalysis of a target-control scatterplot of che loss ratios also indica tes that the target area experienced relatively smaller hail losses du ring the NDCMP period. An inference that the difference can be attribu ted to the NDCMP seeding operations appears to be justified, and the r eduction in hail insurance loss ratios in the target area during the N DCMP years is estimated to be about 45%.