Eventi piovosi estremi: loro valutazione con diversi strumenti di misura e affidabilità delle misure

Many instability processes occurring along the minor hydrographic network and on hillsides are the result of intense hydrological events, often involving large volumes of detritic material which may be rapidly washed downhill, with the risk of impacting on population centres with consequent loss of lives and major socio-economic damage. Many cases have been observed in which the quantity of rainfall, and especially of intense rainfall, should not by itself trigger the process, even though it may be recorded at stations in significant planoaltimetric locations. However, it should be borne in mind that even a few millimetres of rainfall may set the process in motion, if the volume of water is concentrated in a very short time period and if it falls on extensive walls of impermeable rock such as are often found above the gullies and moraine slopes where these phenomena tend to arise. To define possible landslide events, or susceptibility to landslides, and thus the risks associated with them, the availability of precise, dedicated analyses which can accurately establish how the processes are triggered is of fundamental importance. This is why much applied research is devoted to recognising the triggering conditions, the behaviour of the processes during the phase when they are developing along slopes and torrent channels, and how they stop in areas of conoids and on the valley floor, where appropriate measures must be taken to limit the risks of flood damage to the population centres situated there.