Assessing the role of regional characteristics in estimating the volume of glacial lakes in the upper Indus-Ganga-Brahmaputra basins, Hindu Kush Himalaya

Glacial lakes have exponentially increased in the recent decades across the world’s mountains, particularly in the Hindu Kush Himalaya (HKH), caused by rapid melting of glaciers. Consequently, their water volume and hence the hazard potential had also increased in recent decades. Robust water volumes of hazardous glacial lakes located in remote locations are rarely available, limiting the accuracy of current glacial lake outburst flood (GLOF) models that heavily rely on empirical water volume estimation equations. The majority of presently used equations are mainly based on data collected in the European Alps and have limited applicability in the HKH region. Thus, accurately predicting GLOF extents and likely damages in the downstream regions remains a critical challenge in the HKH region. In this study, we developed eight empirical equations to estimate mean depth (4) and volume (4) of glacial lakes in the upper Indus-Ganga-Brahmaputra (IGB) river basins. The study is based on a field-based bathymetric dataset of 25 glacial lakes from different parts of the upper IGB river basins. Separate equations were formulated for the major basins to understand the influence of regional lake characteristics on depth and volume estimations of glacial lakes. Our analysis revealed a non-linear negative relationship between the circularity ratio of glacial lakes and their mean depth, indicating that elongated lakes tend to be deeper than the circular ones. The average circularity ratio of glacial lakes in the upper IGB basins was 0.51 (as of 2020). We estimated the mean depth and total volume for a dataset comprising 19,284 glacial lakes in the upper IGB basins. The estimated mean depth and total estimated volume of these lakes in 2020 was 7.20 m and 28.88 km³, respectively. The empirical equations generated in the study based on the field-based bathymetry will be helpful in assessing the GLOF threats from continuously expanding glacial lakes in the upper IGB basins.