Abstract
Hail is an important economic problem in several countries, and there would be a need for climatological studies not limited to general data such as space and time frequencies of ordinary hailfalls. A large network of hailpad stations, which operated continuously in southwestern France since 1988, gives the first opportunity to compute return periods of very severe point hailfalls characterized either by the total kinetic energy of hailstones or by the diameter of the largest hailstones. The Gumbel distribution has been used to represent the probability density function of the maximum annual value of these two parameters. Preliminary results indicate that the area located just north of the central Pyrenees is three times more exposed to damaging hailfalls than the Atlantic border. The results show that the computation of an areal return period depends upon the hailpad network density, which makes data normalization necessary for inter-network comparisons. This study also offers the possibility of determining return periods of severe hailfalls at a point. As an example, a provisional estimation indicates that a hailfall with hailstones of 3–4 cm diameter occurs every 22 years at any point in the hail core region north of the Pyrenees. The hope is that this study may be progressively expanded to other European hailed regions in which similar hailpad networks are in operation.
Highlights
Every year, the ‘‘Association Internationale des Assureurs contre la Grele’’ publishes the technical results of the crop hail insurance industry in about 20 countries of the world
A former climatological study of hail in southwestern France has shown that the Atlantic and inland regions should be considered separately (Dessens, 1986)
Because the two regions have about the same extent and hailpad density, an immediate comparison is possible between them, and it shows that return periods of very severe hailfalls are nearly three times shorter in the inland area
Summary
The ‘‘Association Internationale des Assureurs contre la Grele’’ publishes the technical results of the crop hail insurance industry in about 20 countries of the world. Geneve (1961) used data of the French meteorological office and compiled various statistics on hail days, hailfall duration, and hailstone diameters. For France, Plumandon (1901) made a pioneering work in compiling the insurance data for the 1873– 1892 period, and he found that hail was concentrated around a median line going from the central Pyrenees to Switzerland. He reported several observations on geographical effects and small scale variations of hailfalls. Vinet (2000) related data from the hail insurance and from the hailpad networks of the Association Nationale d’Etude et de Lutte contre les Fleaux Atmospheriques (ANELFA) and Association Climatologique de la Moyenne Garonne (ACMG). The main results of this exhaustive study are reported in Vinet (2001), including what seems to be the most reliable map of hail risk in France
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