Rainfall and debris-flow occurrence in the Moscardo basin (Italian Alps)

The Moscardo Torrent is a small mountain stream in the Italian Alps and presents a high frequency of debris flows. The basin has been monitored since 1989 and both rainfall data and debris flow occurrence have been recorded, these latter through ultrasonic gauges. This paper aims at giving a new contribution on the long debated question of the cause-effect link between rainstorms and debris flow triggering. A sample of 73 rainstorms 15 of which caused debris flows is considered in this study. The main characteristics of rainstorms (total rainfall amount, duration, average and 60 minutes maximum intensity) and antecedent precipitation are analysed. In the Moscardo basin comparatively low-intensity storms are sufficient to trigger debris flows. The results are compared with those of some well-known works on this topic and lead to conclude that, even in a single small basin, rainstorm characteristics play an important role but are not exhaustive in defining debris flow initiation conditions.