Assessing the Hail Risk to Crops and Property in the United States

Rapidly increasing hail damages to property have brought average annual losses to $1.2 billion (in 1997 dollars) during the 1990s, and this has created great concern in the insurance industry leading to efforts to define the hail risk across nation. Since the property-casualty insurance industry has not kept hail loss records, they must rely on available climatological data supplemented by data from field studies to assess hail risk. Hail risk to crops and property at a point or over an area is a function of the target at risk (property or crop) and the hail frequency and intensity. Newly available climatological data based on historical hail records at 930 stations, as collected by the NWS since 1901, has enhanced the capability to assess point risk. Some spatial risk assessments have combined point averages of hail-day frequencies with hailstone sizes to define risk, and others also employed hailstone volume (mass of ice) and wind with hail, based on data from field projects. Those seeking to define the spatial aspects of risk due to very large hailstones, >2.5 cm in diameter, have had to use area-based risk assessments since point data are too short to provide reliable frequencies of these rare events. On-going research is defining the hail damage characteristics for various structural surfaces and roofing materials where most damage occurs. Crop insurance risk studies have combined that industry=s existing data on crop losses across the nation with long-term frequencies of hail days to generate crop-hail risk patterns for setting rates, and their data, which began in 1948, has been used to assess temporal variability of risk. These temporal assessments have also relied on long-term records of hail-day incidences, and both data sets show the magnitude of major features in average hail risk patterns fluctuate as much as 50% in any given 5- to 20-year period but that these major features persist over time. Long-term trends of hail risk reveal increases in the High Plains and Southeast with decreases in the Midwest and West.