Long-term variations of glacier albedo from 1993 to 2025 in the Central Hunza basin

Glacier surface albedo is an important factor affecting glacier ablation, and it plays a crucial role in understanding glacier health and the surface energy balance. However, its temporal and spatial distribution on glaciers is frequently ignored, entailing the use of constant values in melt models, which can cause inaccurate melt estimates. Glacier albedo changes in the 21^st century remain poorly understood.

Past studies highlight a decrease in glacier albedo between 2001 and 2021 in most regions of the Third Pole. However, the glacier response to climate change in the Karakoram region is not fully understood. A large portion of the glacierized area has shown unusual behavior with respect to global glacier shrinkage, commonly known as the “Karakoram Anomaly”.

In this study, we analyzed, both temporally and spatially, the long-term trend of summer glacier albedo from 1993 to 2025, using Landsat 4/5 TM, 7 EMT+, and 8/9 OLI data from Google Earth Engine database. Our study focuses on the Central Hunza basin, a large basin (2383 km²) in Karakoram (Pakistan), hosting around 280 glaciers. This basin has already shown, on average, an almost balanced mass budget in the period 1973-2009. To ensure focusing only on snow free glacier surface albedo, we masked out snow covered areas by means of the OTSU algorithm and also assessed the Snow Line Altitude, in order to investigate also its variations at the glacier and basin scale. To assure data continuity across sensors with different spectral resolution, we performed a harmonization of the Landsat data.

This study emphasizes the importance of not assuming albedo as a constant, since its long-term variability in the region may not follow global trends. This is particularly relevant as glaciers act as the main hydrological resource in this region.