CROP DAMAGE - THE HAIL SIZE FACTOR

Between 1986 and 1992 a research project was developed and carried out on hail climatology and the economic repercussions of hail on agricul ture in Leon (northwestern Spain). A target area with an extent of 682 5 km(2) was defined, within which a network of meteorological observer s was established at an average density of 1 per 17 km(2). A network o f 250 hailpads installed in a grid formation was also laid out over an area of 1000 km(2) inside the target area The frequent occurrence of hailfalls-122 hail days over seven consecutive summers-provided a deta iled database and allowed several climatological studies to be made. C rop damage was also closely monitored and quantified. Barley and wheat were selected as crops on which to base an analysis of the relationsh ip between hailfall characteristics and crop damage. As the resistance of plants to hailstones is held to vary according to their physiologi cal state, four different stages of plant growth were defined, beginni ng with the formation of grain heads. An important conclusion was draw n: the dispersion of percentages of damage always covers the possible variations in resistance caused by the physiological state of the plan ts. As a result, using only minimal information about hailfall charact eristics-namely, the initial reports of observers regarding hailstone size-a working statistical model has successfully been constructed to predict losses to barley and wheat, using data provided by the Leon ha il project.