Geomorphic control on regional glacier lake outburst flood and debris flow activity over northern Tien Shan

The occurrence of these events is favored by the formation of new glacier lakes and the destabilization of moraines and hillslopes due to climate warming. Understanding the frequency-magnitude of these processes is essential for the implementation of Disaster Risk Reduction strategies. However, long-term records of past GLOFs or DFs in the region are almost completely missing, rendering rational hazard and risk assessments difficult. A unique, multi-century dataset of regional GLOF-DF reconstruction for the Tien Shan has been developed based on tree-ring analyses from six different torrential fans. This dataset provides insights into regional processes activity. The results from over 430 disturbed trees growing on six different DF fans suggest frequent GLOF-DF activity since the 19th century, consistent with available historical records. An increase in process activity during the mid-20th century coinciding with phases of glacier stagnation or even slight glacier advances has also been observed. GLOF-DF activity in northern Tien Shan is inversely related to moraine-glacier ratios as well as to glacier area shrinkage rates and fan characteristics, such as slope and depositional area. These findings imply that glaciological and geomorphic features could be used for regional susceptibility assessments in the future. The results presented here are the longest, annually resolved GLOF-DF series in the region, if not worldwide, and constitute a unique dataset to understand process variability. The dataset suggests that GLOF-DF activity is not solely dependent on glacier area shrinkage rates, but also on changes in geomorphic characteristics at the catchment scale. This indicates that regional susceptibility assessments should consider not only glaciological factors but also geomorphic features. The findings of this study have significant implications for climate change adaptation and mitigation of natural hazards and risks in the region. The results of this study provide a valuable tool for Disaster Risk Reduction strategies in the Tien Shan region. By understanding the frequency-magnitude of GLOFs and DFs, regional authorities can develop more effective early warning systems and implement targeted mitigation measures to reduce the impact of these natural hazards. The dataset presented here can be used to inform regional susceptibility assessments and support climate change adaptation efforts in the region.