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Abstract:
Glacier retreat leads to the formation of glacial lakes, which can become potentially dangerous for outburst flooding, posing a serious risk to the lives and infrastructure of mountainous communities. To better manage such risk, frequent mapping and precise monitoring of glacial lakes are essential yet hindered by inaccessible terrain, severe climatic conditions for in-situ measurements, or a tedious manual mapping of coarse-resolution satellite imagery. Here, we propose an enhanced breakpoint method (EBM) that adopts for each lake an individual histogram prepared by applying a dynamical buffer around that lake. We employ EBM to develop the glacial lake inventories for the Astore Basin within the western Himalayas for 2018 and 2019 using ultra-high resolution (~3 m) optical PlanetScope imagery. Our semi-automated EBM outperforms similar methods and precisely maps glacial lakes of all sizes and complexities with little manual mapping and editing using high-resolution imagery from PlanetScope as well as coarser resolution imagery from Sentinel‑2 and Landsat‑8 platforms. Intercomparison of 2018 and 2019 inventories and the existing 2013 inventory revealed heterogeneous lake formations, disappearances, expansions, and shrinkage patterns. In 2013, 196 lakes had a total area of 5.847 km2 and a corresponding volume of 0.073 km3. By 2018, 135 lakes formed newly, whereas 9 lakes drained out, leading to an overall increase in the number of lakes by 64.28% (196) to 322 lakes. Over the five years of 2013–2018, 40 lakes expanded, whereas 147 lakes shrank, resulting in an overall reduction in area by −1.50% to 5.759 km2 and a decrease in volume by −5.56% to 0.069 km3. As compared to 2018, 213 lakes expanded, whereas 98 lakes shrank, experiencing an overall area expansion of 3.83% to 5.98 km2 and an increase in volume by 4.65% to 0.072 km3. These findings suggest that changes for 2018–2019 are higher than that of the 2013–2018 period. Employing daily PlanetScope imagery at ~3 m resolution, the EBM can precisely map and monitor lake evolutions with low latency time to reduce and mitigate outburst flooding risks in complex terrain.
