- 1University of Firenze, Department of Earth Sciences, Florence, Italy (samuele.segoni@unifi.it)
- 2University of Padua, Department of Geosciences, Padua Italy
We propose a national scale landslide nowcasting system for Italy (300,000 km2) by combining rainfall thresholds with a set of spatially explicit risk indicators. The combination of these two very different elements is obtained through a dynamic matrix, which was purposely calibrated to provide an output in the form of five possible levels of expected risk (from R0 to R4). These levels are connected to the growing intensity of expected impacts and a pre-defined confidence in issuing warnings without omitting alarms.
A specific set of rainfall thresholds is defined for each of the 150 alert zones (AZ) in which Italy is divided. The risk indicator is defined at a municipality level. The calibration of the dynamic risk matrix is carried out independently for each AZ, following predefined operational criteria.
The verification of the matrix outputs was satisfactory as no AZs experienced landslides at the R0 level; only two of them had more than 10% of landslides at the R1 level, and most of the AZs had more than 90% of the landslides in the R2 to R4 risk classes. A comparison with a nation-wide dataset of very severe hydrogeological disasters further proved the consistency of the model outputs with the scenarios that occurred during past events, as most part of the impacts occurred in places and times when the matrix outputs were at the highest levels.
The proposed methodology represents a reliable improvement for state-of-the-art territorial warning systems, as it brings two main advances: (1) the spatial resolution is greatly improved, as the basic spatial unit for warning is downscaled from AZs to municipalities (whose average extension, in Italy, is about 1770 and 38 km2, respectively); (2) the outputs can better address the needs of landslide emergency management, as the warning are specifically addressed to small areas based on the expected impacts (since risk indicators are used in the dynamic matrices), rather than on the probability of landslide occurrence.
How to cite: Segoni, S., Nocentini, N., Barbadori, F., Medici, C., Gatto, A., Rosi, A., and Casagli, N.: A nation-wide nowcasting system for Italy combining rainfall thresholds and risk indicators, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7441, https://doi.org/10.5194/egusphere-egu25-7441, 2025.
