Completeness analyses of the Austrian torrential event catalog

Abstract

Natural hazard catalogs provide information on past documented events, often as the most reliable indication to ensure future hazard mitigation performance—influencing both social and economic welfare. For such reasons, knowledge about the completeness is important and allows to define the period for which the historical range of variability of the documented events can be stated. Based on an extensive collection of torrential events in Austria (more than 21,000), a robust completeness analyses is presented, based on historiographic as well as statistical approaches. The analyses are based on a 3 W-standard, “When did it happen?”, “What happened?”, and “Where did it happen?”, for all documented events. Hence, a completeness of the whole torrential event catalog can be assumed, if the yearly number of events is independent of the reporting rate—the number of reported events per year. We further present completeness periods of (i) the documented torrential processes, “floods”, “bedload processes”, and “debris flows” as well as of (ii) the documented event-intensities, “low”, “medium”, “high”, and “extreme”. In a first order analysis, an increase in events for the resulting completion period could not be detected. However, a strong correlation to the total rainfall sum above the 99th percentile seems to be evident.