A Method for Estimating Crop Losses from Hail in Uninsured Periods and Regions

Abstract

The insurance industry, insurance regulatory bodies, and scientists investigating climate change all desire long records of hail losses. Existing loss records for some states cover the 1948?present period; this span is helpful but is not long enough to define trends, possible fluctuations, and extremes adequately. The only other hail data with much longer records are the frequencies of hail days collected at National Weather Service stations since 1901, and a newly developed database for the major hail-loss states that contains hail-day data for 910 cooperative stations for 1901?94. This study tested two methods for estimating the historical loss values using hail-day data; one method produced modified hail-day values found to relate closely to loss values in the nation?s 21 primary hail-loss states. The method involved modifying a station?s hail-day values for each of the crop-season months using insurance-derived monthly hail intensity indices, resulting in an annual hail-intensity-weighted value. These weighted values of each year were combined using all stations in the crop regions of a state. The state-weighted annual indices were compared with the insurance loss values and yielded correlation coefficients of +0.60 or higher in 18 of 21 states; the resulting regression equations were used to estimate the loss values for the 1901?47 period. The temporal fluctuations and trends in the state hail intensity and loss values for 1901?94 showed major regional differences. States in the High Plains had increasing losses and greater variability with time, whereas states near the Great Lakes exhibited decreasing hail losses and variability with time. The approach can also be used to estimate loss values for areas for which historical loss values do not exist.