1Laboratorio de Fisica de la Atmosfera, Universidad de León - Spain
2Association Nationale d’Etude et de Lutte contre les Fléaux Atmosphériques, Toulouse - France
3Laboratoire d’Aérologie, Observatoire Midi-Pyrénées, Université de Toulouse - France
Hail is an important problem, especially at Mediterranean latitudes. A European hail climatology would be a useful tool for economic considerations (damages to crops, greenhouses and roofs, cars, aircraft, etc.) but it does not yet exist, due to the lack of physical measurements. However, a few hail measurement networks are now in operation in some European countries, and their first data give directions for such a future hail climatology.
After 14 years of hail measurements, with about 1000 hailpads scattered on a 70,000 km2 area of southwestern France, it clearly appears that the kinetic energy is not a sufficient parameter to characterize a hailfall, and that at least another one is necessary. It is then proposed to parameterize a point hailfall by its kinetic energy and by the size of the largest hailstones. With the 2, 500 hailfalls recorded from 1988 to 2000 in different regions of southwestern France, the return periods of hailfalls of given energies and maximum diameters are computed in each region, and the effects of the region surface and of the hailpad density are examined. The largest differences are found between coastal and inland regions, and, for the first time, the results give a physical determination of the hail risk in this part of France. It is hoped that this study will be progressively expanded to other hailed parts of Europe.