This paper deals with the risk assessment to alluvial fan flooding at the piedmont zone of carbonate massifs of the southern Apennines chain (southern Italy). These areas are prime spots for urban development and are generally considered to be safer than the valley floors. As a result, villages and towns have been built on alluvial fans which, during intense storms, may be affected by flooding and/or debris flow processes. The study area is located at the foothills of the Maddalena mountains, an elongated NW-SE trending ridge which bounds to the east the wide intermontane basin of Vallo di Diano. The area comprises a wide detrital talus (bajada) made up by coalescent alluvial fans, ranging in age from the Middle Pleistocene to the Holocene. Historical analysis was carried out to ascertain the state of activity of the fans and to identify and map the zones most hit by past flooding. According to the information gathered, the Sala Consilina fans would appear prone to debris flows; in the past these processes have produced extensive damage and loss of life in the urban area. The watershed basins feeding the fans have very low response times and may produce debris flow events with high magnitudes. Taking into account the historical damage, the fan surface morphology, and the present urban development (street orientation and hydraulic network), the piedmont area was zoned and various susceptibility classes were detected. These results may represent a useful tool for studies aiming at territorial hazard mapping and civil protection interventions.

In mountain basins, sediment supply to the fluvial system occurs mainly through episodic geomorphic processes—such as debris flows and other landslide types—whose effectiveness is strongly influenced by the structural connectivity within a catchment. This paper presents a novel data‐driven approach to identify and map areas that are simultaneously susceptible to debris flow initiation and structurally connected to the main channel network (i.e. relevant sediment source areas for predicting and mitigating flood hazards in the river channels). The presented approach comprises: (i) the visual interpretation, delineation, mapping and classification of event‐specific connected and disconnected debris flow areas in three catchments of the Italian Alps; (ii) the development of data‐driven debris flow release susceptibility models that are combined with quantitatively classified index of connectivity (IC) maps; and (iii) a thorough evaluation of the approach, including an assessment of its spatial transferability across the catchments. The main results show: (i) quantitative IC thresholds to discriminate connected from disconnected debris flow release areas; (ii) statistically well‐performing and geomorphically plausible debris flow release susceptibility models for the three basins; (iii) diverse joint debris flow connectivity–susceptibility maps that allow identifying zones which are differently relevant in terms of debris flow connectivity. This work also highlights the spatial transferability of the approach, associated benefits and potential drawbacks, as well as the utmost importance of a thorough combined quantitative and qualitative (i.e. geomorphic plausibility) evaluation of the underlying results. The proposed approach is rather simple and requires few basic input data, and can therefore be applied over vast areas (e.g. to support regional‐scale hazard assessments or sediment management plans).