Pronounced increase in slope instability linked to global warming: A case study from the eastern European Alps

Abstract

In recent decades, slope instability in high‐mountain regions has often been linked to increase in temperature and the associated permafrost degradation and/or the increase in frequency/intensity of rainstorm events. In this context we analyzed the spatiotemporal evolution and potential controlling mechanisms of small‐ to medium‐sized mass movements in a high‐elevation catchment of the Italian Alps (Sulden/Solda basin). We found that slope‐failure events (mostly in the form of rockfalls) have increased since the 2000s, whereas the occurrence of debris flows has increased only since 2010. The current climate‐warming trend registered in the study area apparently increases the elevation of rockfall‐detachment areas by approximately 300 m, mostly controlled by the combined effects of frost‐cracking and permafrost thawing. In contrast, the occurrence of debris flows does not exhibit such an altitudinal shift, as it is primarily driven by extreme precipitation events exceeding the 75th percentile of the intensity‐duration rainfall distribution. Potential debris‐flow events in this environment may additionally be influenced by the accumulation of unconsolidated debris over time, which is then released during extreme rainfall events. Overall, there is evidence that the upper Sulden/Solda basin (above ca. 2500 m above sea level [a.s.l.]), and especially the areas in the proximity of glaciers, have experienced a significant decrease in slope stability since the 2000s, and that an increase in rockfalls and debris flows during spring and summer can be inferred. Our study thus confirms that “forward‐looking” hazard mapping should be undertaken in these increasingly frequented, high‐elevation areas of the Alps, as environmental change has elevated the overall hazard level in these regions.

Quantification of meteorological conditions for rockfall triggers in Germany

“…The direct effect of temperature on the frequency of rock-slope failures in permafrost locations is based on the same mechanism (e.g. Paranunzio et al, 2019;Savi et al, 2021), but does not play a role in our study region. Moreover, there are weathering mechanisms not directly linked to meteorological events that may promote or trigger rockfalls.…”

Suspended sediment and discharge dynamics in a glacierized alpine environment: Identifying crucial areas and time periods on several spatial and temporal scales in the Ötztal, Austria

“…We suggest that hydro-sedimentological events such as one observed in August 2020involving mass movements 535 that were triggered by heavy precipitation and are probably associated with permafrost thaware likely to occur more frequently in the future: In view of expected future developments, such as more frequent high-intensity summer rainstorms (Giorgi et al, 2016), prolonged snow-free periods in summer during which these rainstorms can become erosive (Hanus et al, 2021;Hanzer et al, 2018), the exposure of vast amounts of sediment due to glacier retreat (Carrivick and Heckmann, 2017;Lane et al, 2017) and accelerating permafrost thaw which facili-540 tates more frequent slope-failure events (Savi et al, 2020), heavy precipitation events have the potential to gain in importance drastically with regard to driving sediment export.…”

“…Adding to this, permafrost thaw can destabilize hillslopes and facilitate mass movements (Chiarle et al, 2021;Huggel et al, 2010;Savi et al, 2020). On the other hand, changes in catchment-scale connectivity can provide 60 new pathways or close off old pathways for loose material to the receiving waters (Cavalli et al, 2013;Lane et al, 2017), for example due to the formation of a proglacial lake.…”

Suspended sediment and discharge dynamics in a glaciated alpine environment: identifying crucial areas and time periods on several spatial and temporal scales in the Ötztal, Austria

“…Intense precipitation events, which are projected to increase in intensity and occur more frequently (Bürger et al, 2019;Giorgi et al, 2016;Scherrer et al, 2016), have a higher chance of affecting unfrozen material during prolonged snow-free periods (Kormann et al, 2016;Rottler et al, 2021;Wijngaard et al, 2016) and may thereby lead to a shift in the relative importance of sediment sources. Adding to this, permafrost thaw can destabilize hillslopes and facilitate mass movements (Chiarle et al, 2021;Huggel et al, 2010;Savi et al, 2020). On the other hand, changes in catchment-scale connectivity can provide new pathways or close off old pathways for loose material to the receiving waters (Cavalli et al, 2013;Lane et al, 2017) depending on local preconditions, for example due to the formation of a proglacial lake.…”