Assessing the Karakoram Anomaly from long-term trends in earth observation and climate data

In contrast to the general trend of global glacier recession, several studies have reported stable or advancing glaciers in the sub-basins of the Karakoram – the so-called ‘Karakoram Anomaly’. Snow and glacier ice melt are important components of the hydrological system and represent a major water supply for the region. In the absence of reliable and comprehensive in situ measurements, Earth observation (EO) and remote sensing retrievals of snow water equivalent (SWE), water balance (WB) and hydro-meteorological variables can be used to infer changes in snow/glacier melting. We used linear regression and Mann-Kendall (MK) methods to assess trends in annual and seasonal variables derived from satellite, gridded and reanalysis datasets of the Global Land Data Assimilation System (GLDAS) and Terraclimate. The spatial and temporal pattern of snow accumulation and ablation varies across the study region. The spatial distribution of annual and winter SWE showed a significant (p < 0.05) positive trend in the western Karakoram. This snow accumulation may be attributed to a significant decrease in summertime maximum temperature (Tmax) in the western Karakoram. By contrast, in the eastern Karakoram, significant negative trends in annual WB indicate depletion of water storage. These results, using a different dataset and approach, are consistent with previous studies where glacier mass balances have been found to be stable or positive in the Karakoram, but become more negative further east and into the Himalaya. These changes in hydrology at highly glacierised catchments have considerable implications for water availability and supply to large downstream populations.