Revisiting the 24 year (1994-2018) record of glacier mass budget in the Suru sub-basin, western Himalaya: Overall response and controlling factors

Glacier mass balance time-series measurements have immense importance in comprehending the overall regional hydrology and meteorology of the mountain systems. Such assessments are critical in the Indus River basin (compared to the Ganga and Brahmaputra), which besides having a significant contribution from the glaciers, also exhibits considerable heterogeneity in glacier response. Thus, to quantify this variability in glacier behavior and thereby develop a comprehensive understanding of the past as well as the future evolution of the glaciers, we reconstruct the annual surface mass balance records of 75 glaciers (size >1 km²) in the Suru sub-basin, western Himalaya for the period 1994-2018. We apply a remote sensing-based equilibrium line altitude-mass balance approach, supported by geodetic mass balance estimates (for 18 major glaciers) and limited field measurements. Our findings suggest a persistent negative mass balance of the glaciers (average: -0.69 ± 0.28 m w.e.a^-1, cumulative: -16.56 m w.e), varying from -0.46 ± 0.27 (1997) to -0.79 ± 0.28 (2018) m w.e.a^-1 during the study period. This overall mass loss coincides with an increased temperature (T_avg increased 0.5 °C; T_min increased 0.27 °C; T_max increased 0.06 °C) and reduced precipitation (by 4%) in the valley during 1994-2018, which shows the sensitivity of these glaciers to climate change. Within the Suru sub-basin, smaller, cleaner and high-altitude mountain glaciers of the Ladakh range have experienced greater mass loss (cumulative: -20.88 m w.e) compared to the Greater Himalayan range (cumulative: -13.44 m w.e). We observe latitudinal variability in mass loss in the Western Himalaya, with the highest mass loss rates in the Greater Himalayan Range (>-0.9 m w.e.a^-1) and lowest in the Karakoram Range (<-0.1 m w.e.a^-1), suggesting a transitional response of the Suru sub-basin glaciers (-0.69 m w.e.a^-1). The overall regional picture suggests synchronicity in the mass loss pattern of western Himalayan glaciers, predominantly controlled by the climatic conditions. Meanwhile, the variability in their mass loss rates is attributed to the unique glacier characteristics.