Glacial lake changes and outburst flood risk assessment in the North American Coast Mountains

Glacial lake outburst floods (GLOFs) pose a significant hazard to ecosystems, infrastructure and human populations in high mountain regions. Addressing this challenge requires a comprehensive understanding of glacial lake dynamics, the identification of potentially hazardous lakes, and the quantitative assessment of associated risks. This study addresses GLOF hazards by investigating the temporal evolution of glacial lakes in the North American Coast Mountains using Landsat satellite imagery from 1990 to 2020. The number of glacial lakes increased from 3920 in 1990 to 5056 in 2020 (+29%), with a corresponding total area expansion from 1897.32 ± 117.42 to 2039.21 ± 136.97 km2 (+7.5%) over the 30-year period. The rate of lake expansion accelerated significantly after 2000, rising from 3.0 km2 a−1 in 1990–2000 to 5.6 km2 a−1 in 2000–2020. This trend was primarily driven by glacier retreat, which caused 530 ice-contacted lakes to become detached from their parent glaciers, while 14 ice-contacted lakes transitioned to non-glacier-fed lakes. A quantitative GLOF susceptibility assessment was then conducted using an Equal Weighting method incorporating six indicators (lake area expansion, lake surface elevation, dam height, dam slope, potential ice avalanche source, and potential rockfall source). Among the 766 glacial lakes susceptible to GLOFs, 75 lakes were classified as very high-susceptibility and 125 as high-susceptibility. The Hydrologic Engineering Center's River Analysis System (HEC-RAS) 2D hydrodynamic model was employed to simulate potential outburst flood dynamics (including flow depth, velocity, and inundation extent) for 75 very high-susceptibility lakes and to assess their potential downstream impacts. The hydrodynamics modeling indicates three buildings, ~46.41 km long roads, ~77.18 km2 of nature reserves, and ~ 207.52 km2 of forest areas are under potential threat from GLOFs. Overall, this study provides an integrated framework for identifying potentially hazardous glacial lakes, for quantifying their susceptibility, and for modeling their downstream impacts, and offers a scientific basis for regional GLOF hazard prioritization and mitigation planning.