These types of networks are usually installed in locations of frequent hail (e.g., [1, 4, 5]), since they provide objective hail measurements at low cost. The characteristics of hail in France have been thoroughly analyzed in prior studies, thanks selleck inhibitor to the available record length. Berthet et al. [6] found greater frequency and intensity of hail in the Pyrenean area, which was attributed to proximity of the mountain chains and Ebro Valley in Spain, where frequent mesoscale cyclonic systems develop during summer and cross into France over the Pyr��n��es [7]. Hailfall is a small-scale phenomenon, normally within a few square kilometers [8, 9]. The strong variability in frequency and distribution of hail is attributed to, among other things, its formation process [1].

This variability can occur on different scales, from as small as hydrometeor size to the mesoscale. Although hailpad networks provide useful information on the characteristics of precipitated hailstones, knowledge of the number of measurement points necessary to adequately characterize hail-affected areas has been a crucial problem in numerous studies. This remains an open question in need of further study. In fact, it is very common to find that data from a hailfall point are considered representative of a much larger area. Therefore, one must bear in mind that such data are used in climatological studies as well as in the calibration, validation, and verification of models [10, 11]. The hailpad networks of ANELFA have a high density of points, at which one can obtain objective information on hailfall characteristics.

These networks provide a huge database of hail events, much larger than that typically accumulated from similar networks. Therefore, through analysis of the network data, we can enhance our knowledge of hailfall, especially concerning factors that may be involved in its variability, and even improve the ability to detect any temporal tendencies. In this paper, we first analyze the spatial variability of hail precipitation in southwestern France. Then, we investigate climatic variability of the number of hailpads impacted within the ANELFA network and obtain climatic trends. Then, we focus on analyzing the relationship between orography and hail variability. Finally, we obtain tendencies in other nearby areas (Ebro Valley, Spain, and Southeast France). 2.

Study Area and DatasetANELFA has historical records from four hailpad networks. The two networks with the longest records of hail precipitation measurement are the Atlantic Drug_discovery and Midi-Pyr��n��es networks, in southwestern France.The Atlantic area is nearly flat, with only a few small hills around the vineyards of Bordeaux and in the south. The Pyr��n��es region is mountainous and is crossed by valleys oriented northward in the central part, and eastward in the eastern half [12]. Elevations reach 3km in the central chain [6].