Multi-Decadal Expansion of Potentially Dangerous Glacial Lakes in Central-Eastern Nepal (1992–2024): Remote Sensing Assessment and GLOF Hazard Implications

Abstract. Glacial lakes in the Himalayan regions are expanding rapidly under ongoing climate change, intensifying the risk of Glacial Lake Outburst Floods (GLOFs). This study quantifies multi-decadal area changes (1992–2024) in four Potentially Dangerous Glacial Lakes (PDGLs), Thulagi, Lumding Tsho, Hongu 2, and Lower Barun, located in central-eastern Nepal, using Landsat 5 and Landsat 8 satellite imagery processed within the Google Earth Engine (GEE) cloud platform. Lake boundaries were delineated from post-monsoon (October–November) median composites using the Normalized Difference Water Index (NDWI; threshold = 0.3), supplemented by manual delineation where topographic shadow conditions compromised automated extractions. Area uncertainties were computed using the standard half-pixel buffer method. Non-parametric Mann-Kendall trend tests with Sen’s slope estimator were applied to all lake area time series to evaluate the statistical significance and rate of expansion. Sub-period regression analysis was used to assess acceleration in lake growth. Empirical area-volume scaling was applied to estimate changes in impounded water volume. All four lakes exhibited statistically significant, monotonically increasing area trends over the 32-year study period (Mann-Kendall tau = 1, p < 0.001 for each lake). Lower Barun exhibited the highest expansion rate (Sen’s slope = 0.063 km² yr^-1), growing from 0.77 ± 0.053 km² in 1992 to 2.76 ± 0.13 km² in 2024 (a 258 % increase), with post-2010 expansion accelerating by a factor of 1.35. Lumding Tsho showed a strongly accelerating growth trajectory (R² = 0.96) with a post-2010 rate that more than doubled. The combined estimated additional water volume stored across all four lakes since 1992 approaches 608.6 × 10⁶ m³, representing a GLOF hazard of exceptional and growing scale. The approach demonstrates a scalable and reproducible framework for long-term glacial lake monitoring and hazard assessment, applicable across data-sparse high mountain environment.