A geostatistic approach to the mapping of rainstorm hazard in the Sannio district of the Campania Apennines (Southern Italy)

Abstract

In this note we maintain that the frequent rainstorms in the Sannio district, Campania, Italy, are to all intents and purposes morphogenetic agents. From a documentary survey we have carried out it is evident that this kind of meteorological event greatly influences the lithological, forest and anthropic elements of the landscape, often producing non-reversible changes to the general physiographic order. Besides direct and documentary observations, the effects of rainstorm erosion on the landscape are also clearly cited in the specific literature. We used a geostatistic approach to survey the spatial variability of rainstorm days occurring in the Sannio district (Province of Benevento) and in the surrounding area from 1981 to 1999. The data have enabled us to draw up a map aimed at identifying areas characterised by recurrent rainstorm events. The techniques applied to elaborate the data are those typically used in geostatistic surveying. Firstly, we began with a structural survey with calculation of semivariance. A mathematical model was adapted, then a test of cross validation was applied to the obtained data. Finally, we used the punctual ordinary Kriging as a technique of linear interpolation of the data. All the data were elaborated using MS Windows-compatible software available on the Internet. The result obtained is a map of distribution of the frequency of rainstorm days in the Sannio district and surrounding areas. As regards specifically erosive effects, we can deduce from the map that the areas characterised by the high recurrence of days with violent downpours are potentially those where hydrogeologic instability is or will be particularly marked, with subsequent negative socio-economic consequences and damage to the landscape. In this way, the phenomenon of violent rainstorm days constitutes a significant item in environmental risk.