Tree-ring records reveal the positive feedback between debris flow and climate warming in a periglacial watershed, Eastern Himalaya Syntaxis

Debris flows in periglacial regions can be driven by rainfall and air temperature. The Yarlung Tsangpo Grand Canyon (YTGC) in the Eastern Himalayan Syntaxis has attracted significant attention due to several catastrophic debris flows in recent years. Current research has focused on characterizing specific events, yet lacks long-term data to clarify the recurrence patterns of periglacial debris flows and their potential linkages with climate. Here, we first reconstructed an 80 year debris flow history of a typical periglacial catchment (XuekaGou, XKG) in the YTGC using dendrochronological analysis. From 110 affected trees sampled along channels near the catchment outlet, we identified 11 historical debris flow events from 1940 to the present. This chronology, combined with the unlimited sediment supply in the watershed, reveals both the randomness and predictability of periglacial debris flow occurrences in the XKG. In recent decades, debris flow activity has shown an increasing trend, with small but frequent debris flows causing persistent erosion and deposition in downstream channels and fan areas, exerting a subtle yet cumulative impact on downstream areas. These debris flows are runoff-triggered but show weak correlation with rainfall, whereas they are best explained by the 15-day positive accumulated temperature (Tc15). Our work establishes a novel approach for periglacial debris flow research in remote mountainous regions of China, providing critical insights into the future trajectories of periglacial debris flows under climate change, as well as informing sustainable development in these areas.