The research team, led by Suhail Ahmad of the University of Jammu, tackled a problem that has long frustrated glaciologists. Glacial lakes sit in remote, often inaccessible terrain, and mapping them by hand across decades of satellite imagery is slow, expensive, and inconsistent. Instead, the team harnessed Google Earth Engine, a cloud-computing platform capable of processing vast archives of satellite data in parallel. They drew on Landsat 5 Thematic Mapper and Landsat 8 Operational Land Imager imagery, both at 30-meter resolution, restricting their analysis to post-monsoon images from September through November, when seasonal snow cover is minimal and lake boundaries are most clearly visible against the surrounding terrain.

At the heart of the automated workflow lies a spectral technique called the Modified Normalized Difference Water Index, or MNDWI, which contrasts the reflectance of water in green and shortwave-infrared bands. Water absorbs strongly in the shortwave infrared, so lakes stand out sharply, while the modification helps suppress confusion with terrain shadows that plague ordinary water indices in steep mountain topography. The researchers refined the approach with an additional threshold on red-band reflectance, exploiting the fact that snow reflects more than half of incoming red light while clear water reflects very little. A slope filter derived from the ASTER Global Digital Elevation Model excluded pixels steeper than 20 degrees, since lake surfaces are inherently flat, and morphological opening operations stripped out spurious noise pixels before manual refinement removed river channels and other non-glacial water features.

The validation was rigorous. For each benchmark year, the team generated 500 stratified random validation points, half lakes and half non-lakes, and interpreted each one against high-resolution imagery in Google Earth Pro. The 1990 map achieved an overall accuracy of 88.6 percent with a Kappa coefficient of 0.772, while the 2025 map improved to 92.4 percent accuracy and a Kappa of 0.848. Field observations at the Durung Drung Glacier in 2024 provided qualitative confirmation, revealing a well-developed proglacial lake in direct contact with the glacier terminus, complete with debris-covered ice, exposed ice cliffs, and supraglacial meltwater channels, all signs of active ablation in terrain ringed by unstable moraine slopes.

The headline numbers tell a story of proliferation rather than dramatic swelling. Total lake area grew only modestly, from 34.81 to 37.72 square kilometers, an average gain of about 0.083 square kilometers per year. Yet the count of lakes surged by 205.5 percent, and 520 of the lakes mapped in 2025 did not exist at all in 1990. Remarkably, every one of the 255 lakes identified in 1990 still persisted through 2025, meaning the entire increase came from new formation rather than loss. The size distribution is starkly skewed: 99.5 percent of lakes in 2025 were smaller than one square kilometer, while just four lakes exceeded that threshold yet contributed disproportionately to the total water stored on the landscape.

This pattern, the authors argue, reflects how deglaciating mountains actually evolve. As glacier snouts retreat and ice thins, overdeepenings and depressions in freshly exposed bedrock and moraine fill with meltwater, spawning swarms of small proglacial and supraglacial ponds. Because each new pond is tiny, the cumulative area gain stays modest even as the lake count explodes. Elevation analysis reinforced the topographic control on this process: the overwhelming majority of lakes cluster between 4,000 and 5,000 meters above sea level, a band where glacier retreat, surface melting, and suitable basin geometry converge. Below that zone, glaciers are scarce; above it, cold limits meltwater supply.

The proliferation matters because glacial lakes are the reservoirs behind potential disasters. When a natural dam of ice or loose moraine fails, the impounded water can surge downstream as a glacial lake outburst flood, or GLOF, destroying roads, bridges, hydropower infrastructure, and villages in its path. The Hindu Kush-Karakoram region has a long history of such events, with compiled inventories documenting hundreds of occurrences across High Mountain Asia, concentrated heavily in the Karakoram, and Pakistan recording more GLOF events than any other nation. Many lakes are known to expand rapidly in the period preceding an outburst, making expansion rate itself a diagnostic signal.

To screen the region’s lakes systematically, the team built a hazard framework combining the Analytic Hierarchy Process with a Potential Risk Score Index. Four indicators were weighted by expert judgment grounded in documented GLOF mechanisms: lake area, expansion rate, distance to the nearest active glacier terminus, and topographic potential, represented by the extent of slopes steeper than 30 degrees within each lake’s contributing watershed, terrain capable of generating ice and rock avalanches. Avalanche susceptibility received the highest weight because mass movements plunging into lakes are the principal trigger of past outbursts. Applying the framework to all 775 lakes, the results were broadly reassuring: about 95 percent fell into the very low, low, or moderate hazard classes. But 36 lakes scored high and four scored very high, together just over 5 percent of the inventory, sharing the dangerous combination of rapid expansion, close glacier contact, large upstream catchments, and steep surrounding walls.

The study’s authors are careful about attribution. The Western Himalaya has warmed by roughly 0.9 degrees Celsius since the early twentieth century, with most of the increase after the 1970s, and warming rates within the Upper Indus Basin range from 0.07 to 0.55 degrees per decade, with projections suggesting median increases of about 3.3 degrees Celsius by century’s end under a moderate emissions scenario. Yet the team explicitly notes that it did not statistically test the relationship between lake evolution and temperature, precipitation, or glacier mass balance, so warming should be viewed as a plausible contributing driver interacting with local geomorphology rather than a proven sole cause. Gridded climate data for the Zanskar region confirm the strongly continental, cold-arid regime, with melt concentrated in the July-August ablation season.

The researchers also acknowledge the limits of their screening tool. Thirty-meter Landsat pixels blur the boundaries of very small lakes, lake volume and depth remain unknown without bathymetry, and moraine-dam composition and stability cannot be assessed from orbit. The Potential Risk Score Index is therefore a first-order prioritization, not a prediction of flood probability or magnitude. Future work, the authors suggest, should integrate higher-resolution imagery from Sentinel-2 and PlanetScope, surface elevation measurements from ICESat-2 and SWOT, field-based bathymetry, and hydraulic flood modeling to convert hazard rankings into concrete estimates of inundation extent and downstream risk. For now, the inventory establishes a critical baseline: forty lakes in the Upper Indus Sub-Basin now demand priority monitoring, and the number of such lakes will likely only grow as the region’s glaciers continue their retreat.

Subject of Research: Multi-decadal automated mapping of glacial lakes and outburst flood hazard assessment in the Upper Indus Sub-Basin, Western Himalaya

Article Title: Automated mapping and multi-decadal changes in glacial lakes in the Upper Indus Sub-Basin, Western Himalaya, using Google Earth Engine

Article References: Ahmad, S., Jasrotia, A. S., Singh, K. K., Sharma, A., & Ridwan, Q. (2026). Automated mapping and multi-decadal changes in glacial lakes in the Upper Indus Sub-Basin, Western Himalaya, using Google Earth Engine. Discover Geoscience, 4(1), Article 392. https://doi.org/10.1007/s44288-026-00761-6

Image Credits: AI Generated

DOI: 10.1007/s44288-026-00761-6

Keywords: glacial lakes, Upper Indus Basin, Western Himalaya, Google Earth Engine, GLOF, remote sensing, Landsat, MNDWI, glacier retreat, climate change, hazard assessment, cryosphere