Risk evolution: how can changes in the built environment influence the potential loss of natural hazards?

Abstract. Alpine areas often suffer significant loss and damage due to a range of natural processes such as landslides, debris flows, snow avalanches or floods. Sealing of the soil surface, settling in endangered areas and enhanced human intervention in the natural settings, as well as socio-economic changes, increase the risk and susceptibility of built environments to natural hazards and the costs of the consequences in a spatio-temporal context. The present study examines the loss estimation of a particular debris flow event for different points in time. The event occurred in August 1987, affected the municipality Martell in South Tyrol, Italy, and resulted in a total cost of € 25 million. The approach presented in this paper focuses on the changes of the land use and settlement expansion in the area since 1954 and attempts to assess the monetary impact of a similar event, which could have happened before (1954, 1985) or following the actual event (1992, 1999, 2006). The method applied is based on the use of a vulnerability curve which was developed for the specific area, based on the documentation of the damage of the 1987 event. Based on this curve, a loss estimation was carried out in order to visualise the risk evolution in a period of 52 yr (1954 to 2006). The results show a significant increase in the extent of the built environment (number, size and value of buildings) which consequently reflect an increase of the potential overall loss through the years. The method can be used in order to assess the potential loss for future scenarios based on different spatial patterns of the built environment.