Impacts of Glacier Activity on Glacier Debris Flow Evolution in a Changing Climate

It has been widely recognized that global warming induces glacier retreat and shrinkage in the cryosphere since the mid-20th century. Such landform and glacier activity changes in the glacierized environments not only perturb the downstream hydrological conditions, but also provide favorable conditions for glacial debris flow hazards and threaten the downstream residents, industrial facilities, and hydropower stations, especially in High Mountain Asia. Quantitatively analyzing frequency-size change of glacier debris flow in a warming climate and finding its early warning indicators are critical for disaster assessment and mitigation. In this study, multi-source long-term remote sensing images and meteorological monitoring data, combined with field data, were applied to analyze the hazardous response of retreating glaciers to climate warming in Southeast Tibet. Eventually, 110 glacial debris flow events were identified from 1986-2023. These events were induced by four identified reasons: glacier lakes outburst flood (GLOF), ice-rock avalanches, precipitations, and surge of meltwater. Based on the time series catalog, it can be found that the glacial debris flow has shown the increasing frequency and scale since 1973, and the frequency of the debris flows induced by moraine landslides and ice-rock avalanches in steep terrain has increased. In the past four decades, climate change has led to complex responses in glacier activities, characterized by increased activity of smaller glaciers (high-altitude hanging glaciers) and weakened activity of glaciers in large valley. In the future, the continuous retreat of glaciers will promote the disappearance of icefalls and the development of larger-scale hanging glaciers with heightened activity, which will increase the frequency of ice-rock avalanche induced debris flow. During the evolution process of these glacial debris flows, we found four possible indicators for event warning, including crevice density, glacier velocity, glacier geomorphology change (icefall disappeared), and expanding glacial lakes.