Climate Warming Triggered a Glacial Lake Outburst Flood and Debris Flow Events in an Alpine Watershed, Western Himalayas, Tibet Plateau

In the Tibet Plateau, Glacial Lake Outburst Floods (GLOFs) and associated debris flow events have been gradually increasing in the alpine regions of West- and Trans-Himalayas due to a notable rise in both the frequency of extreme rainstorms and the effects of climate warming. This article documents GLOFs in Rongdui watershed, Western Himalayas (China), on October 5, 2021. Data records were extracted from multiple resources to thoroughly examine the climatic conditions. These data are from a local meteorological station, the Sentinel-3 Sea and Land Surface Temperature Radiometer (SLSTR) thermal bands, pre- and post-flow high-resolution sensing maps, the small baseline subset InSAR time-series technique (SBAS-InSAR), water release, eroded moraine debris, and the topographic change. The released water approximately reached 59.5 × 10⁴ m³, strongly affecting at least 158.6 × 10⁴ m³ of moraine debris to form debris flows. The potential cause of this change is high temperatures in the summer season in 2020 and late September 2021, leading to a glacier lake expansion and the corresponding GLOFs events. Though a large amount of moraine debris was entrained to form debris flows, the majority of it has been deposited in the wide and low-gradient valley floor area. Results from SBAS-InSAR prove that the moraine dam failure and the glacial till exhibit obvious subsidence before GLOFs events. Importantly, a direct correlation between moraine dam displacements and temperatures was observed, which could be further examined for hazard warning in the future. This case study reveals that the characteristic of deposits is finer in midstream and on fan areas than in other locations. The interior porewater pressure is substantial, with slower dissipation downstream than upstream, which may result in a long-runout behavior of debris flows. Lastly, the possibility of long-runout debris flows could increase due to the lag effect of GLOFs after years of high temperatures, highlighting the necessity for extra attention to the potential risks in West- and Trans-Himalayas.