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.
Highlights
In Alpine regions, human settlements, infrastructures and environmental resources are frequently endangered by flood or bedload transport processes and mass movements like debris floods or debris flows
Such torrential processes differ in their formation, procedure as well as dynamic behavior, and they are all related to occur in steep headwater catchments often associated with a high density of population
In Austria, studies about hazard assessment procedures for torrential processes started at the end of the 19th century (Duile 1826; Müller 1857; Landolt 1886; Stiny 1907, 1909), and since there has been a shift from heuristic hazard reduction strategies to a quantified risk culture
Summary
In Alpine regions, human settlements, infrastructures and environmental resources are frequently endangered by flood or bedload transport processes (flood events with high sediment transport rates) and mass movements like debris floods or debris flows Such torrential processes differ in their formation, procedure as well as dynamic behavior, and they are all related to occur in steep headwater catchments often associated with a high density of population. In countries like Austria, people always meet a challenge to find an accurate balance between the imminence of natural hazards and the progress in spatial developments For this reason, awareness of natural hazards is high, and reports of catastrophic events related to these kind of processes can bedated back to the early middle ages. The reliability of modern risk reduction strategies for natural hazardous processes depends on messages from the past, either from event documentations, stratigraphic analysis, or analysis of geomorphological field traces
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