Quantitative evaluation of the debris flow events in July 2022 in Horlachtal/Austria by combining different data sets

In order to calibrate and validate debris flow models, high precision in situ measurements are essential. However, it is quite difficult to acquire detailed information about debris flows, as they only rarely occur during exceptional high precipitation intensities. In July 2022, a series of such high-intensity short-duration precipitation events triggered several debris flows within the area of the Stubai Alps/Austria, which caused severe damage. On the 20^th and 23^rd of July 2022, two of these convective events initiated multiple debris flows on the slopes of the Horlachtal, a side valley of the Oetztal.

These events have been registered by measurements of three different meteorological stations and four different discharge gauges distributed over the study area. In addition, INCA (Integrated Nowcasting through Comprehensive Analysis) rainfall data provided by ZAMG (Austrian Central Institute for Meteorology and Geodynamics) allow insights in the spatial and temporal characteristics of the rainfall patterns. Furthermore, two airborne LiDAR (Light Detection and Ranging) campaigns of the Chair of Physical Geography at the University of Eichstätt-Ingolstadt covering the whole Horlachtal (about 55 km²) provide detailed pre and post event topographical data.

A combined evaluation of the different data sets allows us to characterise the debris flow events in the study area in great detail. Topographical analyses show that a total number of 156 debris flows were triggered with accumulation volumes up to 40.000 m³. These volumes can be related to the individual catchment areas in combination with precipitation intensities. Furthermore, the spatial distribution of the triggered debris flows show a concentration to a certain region within the study area, which relates to the spatial patterns of the precipitation events.