Some observations on the use of data from historical documents in debris-flow studies.

The knowledge of past events is important for the assessment of debris-flow hazard. Amongst the sources of information, documents from historical archives are particularly important in sites where the debris flows cause damage to urban areas and transportation routes. The paper analyses the availability of historical documents on debris flows in Northeastern Italy and discusses factors that can influence the building of time series from archive data both at regional and single basin scales. An increased number of debris flows was observed in the studied region for the last decades. This could be due both to an increased frequency of the events and to a larger availability of information: the analysis carried out indicates that the latter factor is probably the most influencing. The importance of factors, which affect the collection of data, including the conservation of documents and the presence and fragility of the elements at risk, is stressed in view of a wise use of historical data on debris flows.