Rainfall thresholds for landslide early warning system in Sardinia

The Research Institute for Geo-Hydrological Protection of the Italian National Research Council (IRPI CNR) has developed in cooperation with Civil Protection of Sardinia Region, a regional early warning system for the possible occurrence of rainfall-induced landslides (SARF Sardinia), which currently compares the national rainfall thresholds with the rainfall measured by national and regional rain gauge networks and with rainfall forecasts provided by COSMO-I5 and BOLAM models. In the framework of the current Collaboration Agreement between the Sardinia Region and IRPI CNR, a catalogue containing meteorological and hydrogeological information related to rainfall-induced landslides in Sardinia has been compiled. The catalogue lists 261 landslides that occurred in the period 2007-2020. The information includes: (i) event identifier; (ii) rainfall data (name and geographic coordinates of the selected rain gauge, duration, rainfall mean intensity, and cumulated rainfall responsible for triggering); (iii) landslide geographic data (region, province, municipality, location affected by the event, geographic coordinates of the landslide, spatial accuracy of the landslide); (iv) landslide type; (v) landslide temporal data (year, month, day, time, temporal accuracy of the landslide); and (vi) source of data/information. Rainfall series used to reconstruct the landslide triggering conditions include measurements of 186 rain gauges from a Regional Agency network (SASI), 186 additional stations provided by the Environmental Protection Agency of the Region of Sardinia (ARPAS) and the former Hydrological Service (ExSI), and 96 rain gauges from the National Department for Civil Protection network. Information on rainfall-induced landslides comes from digital and printed newspapers, blogs, technical documents, landslide event reports, and fire fighter reports. The information in the catalogue is used to define regional rainfall thresholds to be implemented in the SARF Sardinia. Thresholds are defined using the frequentist method, which allows the calculation of cumulated event rainfall-rainfall duration (ED) threshold curves corresponding to different non-exceedance probability levels and including uncertainty in the parameters that define the thresholds. Currently, the Civil Protection of Sardinia Region is using the implemented system to support decisions in order to issue warning advices.