Debris Flow Activity in Permafrost Regions in Austria During the 20th Century

Abstract

Debris flows typically result from a critical combination of relief energy, water, and sediment. Hence, besides water-related trigger conditions, the availability of abundant sediment is a major control on debris flows activity in alpine regions. Increasing temperatures due to global warming are expected to affect the periglacial environment and by that the distribution of alpine permafrost and the depth of the active layer. This might lead to increased debris flow activity and increased interference with human interests. Here we assess the importance of permafrost on documented debris flows in the past by connecting the modeled permafrost distribution with a large database of historic debris flows in Austria. The permafrost distribution is estimated based on the model PERMAKART 3.0, which mainly depends on altitude, relief, and exposition. The database of debris flows includes more than 4500 debris flow events in around 1900 watersheds in the Austrian Alps. We find that around 10% of documented debris flows occurred in watersheds having a permafrost fraction larger than 5% in their headwaters. Only around 50% of historic debris flow events were documented in watersheds where permafrost is clearly absent. Our results indicate that watersheds without permafrost experience less, but more intense debris flow events than watersheds with modeled permafrost occurrence. We find no trend of increased debris flow occurrence rate from permafrost regions in recent years. Our study aims to contribute to a better understanding of geomorphic activity and the impact of climate change in alpine environments.