Spatio-temporal analysis of slope-type debris flow activity in Horlachtal, Austria, based on orthophotos and lidar data since 1947

Abstract

In order to get a better understanding of the future development of alpine slope-type debris flows in the frame of climate change, complete and gapless records of the last century for this type of geomorphologic process are necessary. However, up to now such records have been scarce. Here, the slope-type debris flow activity in Horlachtal, Austria, has been investigated since 1947 with the help of historic and recent area-wide remote sensing data. Using geomorphological mapping, both spatial and temporal variabilities in debris flow dynamics can be shown. The results indicate short-term variations rather than consistent increasing or decreasing trends of slope-type debris flow activity in Horlachtal. Specifically, three active periods between 1954 and 1973, 1990 and 2009, as well as 2015 and 2018, can be registered. Analyses of the deposited debris flow volumes show that for parts of the study area the largest volumes appeared in the early 1990s, which might have even influenced the dynamics in the following years. Studies on the spatial variabilities revealed differences of slope-type debris flow activity within the study area and point to local rainfall events as triggers. However, long-term precipitation data of high temporal resolution of two alpine meteorological stations do not reveal increasing or decreasing trends in the occurrence of such events.