In many areas, rainfall is the primary trigger of landslides. Determining the rainfall conditions responsible for landslide occurrence is important, and may contribute to saving lives and properties. In a long-term national project for the definition of rainfall thresholds for possible landslide occurrence in Italy, we compiled a catalogue of 186 rainfall events that resulted in 251 shallow landslides in Calabria, southern Italy, from January 1996 to September 2011. Landslides were located geographically using Google Earth®, and were given a mapping and a temporal accuracy. We used the landslide information, and sub-hourly rainfall measurements obtained from two complementary networks of rain gauges, to determine cumulated event vs. rainfall duration (ED) thresholds for Calabria. For this purpose, we adopted an existing method used to prepare rainfall thresholds and to estimate their associated uncertainties in central Italy. The regional thresholds for Calabria were found to be nearly identical to previous ED thresholds for Calabria obtained using a reduced set of landslide information, and slightly higher than the ED thresholds obtained for central Italy. We segmented the regional catalogue of rainfall events with landslides in Calabria into lithology, soil regions, rainfall zones, and seasonal periods. The number of events in each subdivision was insufficient to determine reliable thresholds, but allowed for preliminary conclusions about the role of the environmental factors in the rainfall conditions responsible for shallow landslides in Calabria. We further segmented the regional catalogue based on administrative subdivisions used for hydro-meteorological monitoring and operational flood forecasting, and we determined separate ED thresholds for the Tyrrhenian and the Ionian coasts of Calabria. We expect the ED rainfall thresholds for Calabria to be used in regional and national landslide warning systems. The thresholds can also be used for landslide hazard and risk assessments, and for erosion and landscape evolution studies, in the study area and in similar physiographic regions in the Mediterranean area.

On 1 October 2009, a high intensity storm hit the Ionian coast of Sicily, SW of Messina, Italy. The Santo Stefano di Briga rain gauge, located 2 km W of the Ionian coast, recorded 225 mm of rain in seven hours. The intense rainfall event triggered abundant slope failures, and resulted in widespread erosion and deposition of debris along ephemeral drainage channels, extensive inundation, and local modifications of the coastline. Landslides occurred in a territory prone to slope failures, due to the local geological and geomorphological settings. Many landslides were related to the presence of roads lacking adequate drainage. Abandoned terraced slopes lacking proper drainage, and unmaintained dry walls were also related to slope failures. Damage was particularly severe in small villages and at several sites along the transportation network. The shallow landslides and the inundation resulted in 37 fatalities, including 31 deaths and six missing persons, and innumerable injured people. After the event, an accurate landslide inventory map was prepared for the Briga and the Giampilieri catchments. The map shows: (i) the distribution of the event landslides triggered by the 1 October 2009 rainfall event; (ii) the distribution of the pre-existing slope failures; and (iii) other geomorphological features related to fluvial processes and slope movements. The landslide inventory map was prepared at 1:10,000 scale through a combination of field surveys and photo-interpretation of pre-event and post-event, stereoscopic and pseudo-stereoscopic, aerial photography. Different types of aerial photographs were analysed visually to prepare the landslide inventory map. The event landslides were mapped through the interpretation of pseudo-stereoscopic colour photographs taken shortly after the event at 1:3500 scale, combined with digital stereoscopic photographs at approximately 1:4500 scale, taken in November 2009. The pre-event landslides and the associated geomorphological features were mapped using 1:33,000 scale aerial photographs flown in 1954, 1955, and 2005. The event and pre-existing landslides were checked in the field in the period October–November 2009.

Temporal properties of 152 575 rainfall events, recorded at time steps of 5 min, having different durations and occurring between 1989 and 2008 at 155 localities of Calabria (Italy), have been analysed in this paper. Samples from 45 533 storms have been selected to classify rainfall events as "significant" with regard to their contribution to soil erosion, flooding and/or other geo-hydrological processes. The samples are representative of a wide variety of situations in terms of duration, total rainfall, intensity, etc. The use of standardized rainfall profiles (SRP) is proposed to describe the within-storm temporal pattern. The main attraction of this method lies in the fact that it is based on actual data of regional precipitation. Its weak point is that large samples of data are required to obtain regional profiles. The research necessities for improving the use of Huff curves for storm disaggregation and its the potential use are summarized in this paper on the basis of the specific literature. A new criterion – based on the comparison of the areas A₁, A₂, A₃ and A₄ that underlie the four 25% of durations of a given SRP, and the corresponding four values of the "uniform" SRP (USRP), is suggested here with the aim of improving the use of the information content of SRP. Some interesting results concerning the sample frequency and the characterization of parameters for hydrological applications are commented on. The study conducted so far has produced important, albeit preliminary, results for different contexts of Calabria concerning the use of SRP among the methods for constructing design storm hyetographs.

Heavy rainstorms often induce flash flooding, one of the natural disasters most responsible for damage to man-made infrastructures and loss of lives, also adversely affecting the opportunities for socio-economic development of Mediterranean countries. The frequently dramatic damage of flash floods are often detected, with sufficient accuracy, by post-event surveys, but rainfall causing them are still only roughly characterized. With the aim of improving the understanding of the temporal structure and spatial distribution of heavy rainstorms in the Mediterranean context, a statistical analysis was carried out in Calabria (southern Italy) concerning rainstorms that mainly induced flash floods, but also shallow landslides and debris flows. Thus, a method is proposed – based on the overcoming of heuristically predetermined threshold values of cumulated rainfall, maximum intensity, and kinetic energy of the rainfall event – to select and characterize the rainstorms able to induce flash floods in the Mediterranean-climate countries. Therefore, the obtained (heavy) rainstorms were automatically classified and studied according to their structure in time, localization, and extension. Rainfall-runoff watershed models can consequently benefit from the enhanced identification of design storms, with a realistic time structure integrated with the results of the spatial analysis. A survey of flash flood events recorded in the last decades provides a preliminary validation of the method proposed to identify the heavy rainstorms and synthetically describe their characteristics. The notable size of the employed sample, including data with a very detailed resolution in time that relate to several rain gauges well-distributed throughout the region, gives robustness to the obtained results.