Landslide Triggering and Local Rainfall Thresholds in Bradanic Foredeep, Basilicata Region (Southern Italy) Maurizio Lazzari, Marco Piccarreta, and Domenico Capolongo Abstract It is recognised that a lot of the landslides occurred in the Mediterranean region are triggered by short intense storms. Due to its geological, geomorphological and climatic settings, the Bradanic Foredeep (Basilicata region) is affected by the widespread presence of landslides. The main objective of this paper is to identify the empirical triggering thresholds in Bradanic Foredeep and to investigate the role of antecedent rainfall. Using a variety of information sources, we have compiled a catalogue listing 97 rainfall events linked to landslides triggering in the investigated area. For each event in the catalogue, the exact or approximate location of the landslide and the time or period of initiation of the slope failure is known, together with information on the rainfall duration D, and the rainfall mean intensity I , that have resulted in the slope failure. The local rainfall threshold for the study area has been established using the statistical Frequentist approach. The comparison with regional thresholds proposed for other Italian regions has revealed that the Bradanic Foredeep thresholds are lower; which is probably due to the different quality of rainfall dataset. In fact, all the previous threshold have been evaluated starting from hourly data, while for the Basilicata region only daily data are available. Throughout this study we could not identify a significant correlation between antecedent rainfall and critical rainfall. Keywords Rainfall-induced landslides  I-D relation  Bradanic Foredeep  Southern Italy Introduction The Mediterranean region is particularly sensitive to changes in the frequency and intensity of extreme rainfall events, which are often related with disastrous geo- hydrological events, such as floods and landslides (Luino 2005). Italy is one of the most vulnerable countries in terms of exposure to natural hazards within the Mediterranean (Guzzetti et al. 2005). The area affected by hydrogeological risk is 21,505 km 2 , which corresponds to the 7.1 % of the whole territory. From 1991 to 2001 more than 1,000 flood events occurred (Ministero dell’Ambiente 2003). In only 1 year, 2003, major floods affected more than 300,000 people and caused damage up to 2,184 million euro. In this paper we analyze the record of extreme rainfall events and landslides in Bradanic Foredeep, an eastern sector of southern Italian region Basilicata. In Basilicata the area affected by flood risk is 260 km 2 (2.6 % of the whole territory) and 58 % of the 114 municipalities are classified at high risk and a further 13 % at very high risk of land- sliding (Clarke and Rendell 2006). In the investigated area slide surfaces are often associated with contacts between unconfined aquifers in sandy-conglomerate layers and under- lying impermeable clays and shales (Gostelow et al. 1997). M. Lazzari (*) Institute of Archaeological and Monumental Heritage, National Research Council, 85050 Tto Scalo (PZ), C.da S, Loja, Italy e-mail: m.lazzari@ibam.cnr.it M. Piccarreta  D. Capolongo Department of Geology and Geophysics, University of Bari, Via Orabona, 4, Bari, Italy C. Margottini et al. (eds.), Landslide Science and Practice, Vol. 2, DOI 10.1007/978-3-642-31445-2_88, # Springer-Verlag Berlin Heidelberg 2013 671