A supply-limited torrent that does not feel the heat of climate change
Jiazhi Qie, Adrien Favillier, Frédéric Liébault, Juan Antonio Ballesteros‐Cánovas, Jérôme Lopez‐Saez, Sébastien Guillet, Loïc Francon, Yihua Zhong, Markus Stoffel, Christophe Corona
Abstract
Debris-flow activity in the Alps is anticipated to undergo pronounced changes in response to a warming climate. Yet, a fundamental challenge in comprehensively assessing changes in process activity is the systematic lack of long-term observational debris-flow records. Here, we reconstruct the longest, continuous time series (1626-2020) of debris flows at Multetta, a supply-limited torrential system in the Eastern Swiss Alps. Relying on growth-ring records of trees that were damaged by debris flows, we do not detect significant changes in the frequency or magnitude over time. This seeming absence of a direct climatic influence on debris-flow initiation aligns with the regular distribution of repose time patterns, indicating a dependence of local process activity on sediment discharge and recharge. This stark difference in process behavior between our supply-limited site and transport-limited catchments has implications for assessing torrential hazard and risk mitigation in a context of global warming. Reconstruction of debris flows in a supply-limited system shows that process activity is controlled by sediment supply over multi-decadal to centennial timescales. Debris flows recur less frequently here and are, unlike transport-limited systems, not affected by climate change.