An analysis of thirteen years of commercial hail suppression in central Alberta


  • T. Petersen


Weather Modification Operations


This article is a summary of a research project carried out in the Department of Agricultural Economics, University of Alberta, and financed by the Alberta Agricultural Research Trust. The commercial hail suppression project of the Alberta Weather Modification Cooperative (AWMC) and its sole contractor, Irving P. Krick Associates of Canada, is evaluated for their active cloud seeding years 1956 to 1968. An original evaluation done in 1969-70 and reported in 1971, has been supplemented by new hail loss information generated during the subsequent non seeding years 1969 to 1972 for the selected AWMC target area. Because provisions for an effective on-going evaluation of the project were minimal, an "after the fact" post-project evaluation was required in response to controversy over the degree of success achieved by the AWMCin reducing hail losses. Several post-project evaluation models were consequently examined by the author in terms of adequacy and data availability. The decision was made to use the Target Area-Control Area model with hail insurance Loss to Risk Ratios (L/R) as a measure hail damage. Correlation and regression analyses were utilized to draw inferences about the effectiveness of the AWMC project, and tests of statistical significance were applied. High natural variation in hail losses between areas and years created serious statistical difficulties in attempts to isolate any positive or negative effects of the program. This was reflected in results with low levels of statistical significance. Thus strong and assertive conclusions could not be made. Comparison of pre-seeding hail losses with those experienced in the target and control areas during the active seeding program of the AWMC, suggested the possibility of hail damage reduction at low levels of reliability. However, additional "hind sight" hail damage information now available for the post seeding years negates such a conclusion, based on the method of evaluatlon used in thls study. This suggests that the AWMC project was either ineffective, or there was insufficient information available to provide an adequate evaluation. These conclusions are in direct contradiction to those made by Irving P. Krick and Newton C. Stone in Vol. 7, No. 1,WMA 'Journal of Weather Modification', April 1975, titled "Hail Suppression in Alberta 1956-1968".




Technical Notes and Correspondence