A comparison of methods for mapping statistical characteristics of heavy rainfall in the French Alps: the use of daily information / Comparaison de méthodes de cartographie de paramètres statistiques des précipitations extrêmes dans les Alpes françaises: apport de l'information journalière

Abstract

Various methods for mapping heavy rainfall (10-year and 100-year rainfall) at time steps of between 1 and 24 h are compared. These methods are applied to the French Alps, a mountainous region subject to heavy rainfall. Data are obtained not only from recording raingauges (measuring precipitation over short time steps of 1, 2, 3, 6, 12 and 24 h), but also from abundant daily raingauges. Among the methods reviewed, kriging is based only on the interpolation of recording raingauge data. Other methods tested make use of additional information obtained from daily measurements. Daily raingauges are more numerous than recording raingauges in the study region and the more accurate knowledge of the daily rainfall field provides valuable information for time steps of less than 24 h. Another method tested includes relationships between rainfall and topography, of importance in a mountainous region such as the French Alps. All these methods are compared using cross-validation. Comparison shows that topography is indeed an important parameter for short time steps. Using daily information improves mapping for time steps between 6 and 12 h. For the daily time step, the field is always well reconstituted, whatever the method used, since the measurement network is sufficiently dense to ensure accurate interpolation between the measurement points (except for zones at elevations above 2000 m, where there are no measurement stations).