Updating and tuning a regional-scale landslide early warning system

This work presents the last improvements of an operative regional-scale warning system developed for the management of the risk related to rainfall-induced landslides (both shallow and deep seated). The warning system is named Sistema Integrato Gestione Monitoraggio Allerta, and it is based on a set of spatially variable statistical rainfall thresholds (Martelloni et al. Landslides doi: 10.1007/s10346-011-0308-2, 2012). The performance of the warning system was enhanced using a larger landslide dataset for the calibration of thresholds and readjusting the boundaries of the territorial units (TUs, the basic spatial unit of application of the warning system). Our tuning leads to define a larger number of TUs and to change some of the previous reference rain gauges. In particular, a statistical analysis highlighted that the spatial organization of missed and correctly predicted landslides does not depend on lithology, land use, and morphometric attributes; therefore, the redefinition of TUs was based on the administrative borders between municipalities. This allowed combining the TU outputs into a decisional procedure which, in a completely automated way, is able to forecast the warning levels based on objective and quantitative criteria (the number of expected landslides), in full accordance with the regional civil protection guidelines. The implementation of these updates was straightforward and could be conveniently applied to similar warning systems based on rainfall thresholds.