A generic framework for glacial lake outburst flood investigation: A case study of Zalai Tsho, Southeast Tibet

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Glacial lake outburst floods (GLOFs) are one of the most severe natural disasters, resulting in enormous socio-economic losses as well as threatening downstream settlements and infrastructure in the alpine region. Understanding historical GLOFs benefits disaster reduction and landscape conservation, but many GLOF events remain unreported or lack critical attributes. In this study, a novel framework was proposed to detect historical GLOFs and populate related attributes using a combination of Landsat, Sentinel-2 and Planet optical images, Sentinel-1 Synthetic Aperture Radar (SAR) images, field surveys, and documentation. The framework was implemented successfully on the case of Zalai Tsho, which revealed a previously unknown GLOF with critical attributes including the associated lake evolution, the flood process, and the impacts. The Zalai Tsho GLOF event in Bomi County, Southeast Tibet, occurred on July 7, 2018. Zalai Tsho emerged in 1994, and its surface area increased by 178% between 1994 and 2018, followed by a complete disappearance after the dam failure. A total water volume of 2.7 ± 0.2 × 105 m3 was released from Zalai Tsho to generate a peak discharge of 558.4 m3/s estimated by hydrological models, which destroyed a bridge, 23.2 ha of woodland, and 1.7 ha of farmland. The Zalai Tsho GLOF was initiated by intense melting waters, superimposed on water from an upstream supraglacial lake, eventually resulted in serious socio-economic losses and long-term environmental effects. Post-GLOF conservation projects play a positive role in protecting residents against flooding, while soil erosion has been exacerbated in certain areas without artificial countermeasures. This study provided an up-to-date, prototype framework for the identification of historical GLOF events to enrich the GLOF dataset and contributed to the risk assessment of GLOF and landscape conservation.