Rainfall Threshold and Landslides in the Post-orogenic Complex of the Esino River Basin, Central Italy

Hydrogeological hazards are widespread and recurrent in Italy, requiring constant monitoring, prevention and mitigation activities. This paper contributes to the landslide forecast debate, analysing the relationship between rainfall and landslides in the eastward section of the Esino river basin located in the Marche region (central Italy). This area of similar hydrogeological properties is characterized by post-orogenic quaternary sediments prone to rainfall-induced shallow landslides. The preliminary investigation revealed the occurrence of 232 landslides, most of all shallow and small-sized, from 1953 to 2011. Rainfall data from neighbouring rain gauges were compared with the historical series of landslides both on annual and monthly basis. Moreover, the intensity-duration empirical model is applied to describe a new empirical triggering threshold valid for the study area. Threshold rainfall conditions are described by the equation: I = 1.61 x D-0.21 where I = mean rainfall intensity (mm/h) and D = rainfall duration (h). Such equation represents the conditions that in the past decades activated 90 % of all landslides occurred within the area. This rainfall threshold could be used to forecast landslides occurrence in the post-orogenic complex of the Esino river basin.