French Hail prevention project

For the whole of France, crop losses due to hail cost, on average, 0.5 billion euros a year, to which should be added the damages to buildings and vehicles for which there are no national statistics.

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Hail risk in France

The risk mapping indicates that the Southwest and Southeast are the areas most exposed to the phenomenon but the central part of the country and the North-east are equally vulnerable.

Historical background

Besides passive prevention of hail insurances and anti-hail nets, there is a scientific method aimed at reducing hailfall intensity. This method was born about fifty years ago, from two discoveries in cloud physics. Bergeron, a Swedish scientist, first showed that precipitation forms through the icing of precipitation elements in cloudy areas where populations of liquid droplets and ice crystals coexist. Shortly after that first step, American scientists Schaefer and Vonnegut discovered that it was possible to artificially increase the number of ice crystals in clouds and to proportionally decrease the size of the precipitating elements, notably that of hailstones. A convenient way of inducing this increase is to seed the clouds with silver iodide smokes, and the most current applications are fog dispersion, rain stimulation and hail suppression.
As soon as those discoveries were made, several organizations and important people in the agricultural circles of Southwestern France gathered, under the impulse of Professor Henri Dessens to found a non-profit organization in charge of the development of techniques of artificial weather modification aimed at suppressing hail.
ANELFA
This association, born in 1951, still exists and is today called the Association Nationale d’Etude et de Lutte contre les Fléaux Atmosphériques (Association to Suppress Atmospheric Plagues).

Principle

The physical basis of the project is that, since the updraft of the storms feeds with heat and water vapor in the lower layer of the atmosphere, it is logical to seed the storms from silver iodide ground generators. To insure targeting in as many meteorological situations as possible, seeding stations must be spread out in local networks with an odd 10 km mesh. To succeed, the seeding must be performed on young feeder cells, at least 3 hours before the hail risk.

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