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Glacial lakes are widely distributed across glaciated mountainous regions such as Southeast Tibet (ST). As a result of climate change, glacial lakes have expanded continually in ST over recent five decades, and ST is seriously suffering from glacial lake outburst floods (GLOFs). Hence, glacial lake investigations and hazard assessments of GLOFs are very necessary to perform and are of great practical significance for this area. The region running from Ranwu to Tongmai (RTR) in ST was selected as a study area. To assess hazard degrees of GLOFs, nine factors (F1-F9) were selected from glacial characteristics: the scale of glacial lakes, meteorological conditions, moraine dam parameters and downstream gullies. Average monthly (May to September) land surface temperatures (LSTs), temperature change rates, and average annual precipitation levels were first calculated using Moderate Resolution Imaging Spectroradiometer (MODIS) LST product and Tropical Rainfall Measuring Mission (TRMM) precipitation data. Then, glacial lake areas, downstream gully slopes, distances to glacial lakes, upper glacier areas, average gradients of upper glaciers, and terminal moraine dam widths were obtained based on Thematic Mapper (TM) and Operational Land Imager (OLI) images and Digital Elevation Model (DEM) data. Finally, the fuzzy comprehensive assessment (FCA) method was used to assess hazard degrees of GLOFs in the study area. According to the results, 135 glacial lakes existed during the study periods, five new glacial lakes formed due to lake collapse and snow and ice melt, and one disappeared due to GLOFs. The number of glacial lakes in the area increased from 130 in 1986 to 134 in 2015, and the total area of glacial lakes increased from 832.77 ha in 1986 to 850.51 ha in 2015 due to lake expansion and GLOFs. Of the 134 glacial lakes present in 2015, 10 are identified as high hazardous lakes, eight are identified as medium hazardous lakes, two are considered low hazardous lakes, and 114 are considered extremely low hazardous lakes. The results illustrate hazard levels of GLOFs in ST, which can help guide future hazard prevention in the area.