Reconstructing 32 years (1989–2020) of annual glacier surface mass balance in Chandra Basin, Western Himalayas, India.

This study presents a reconstruction of basin scale long-term annual surface mass balance (SMB) estimates for 91 glaciers (≥ 1 km²) of Chandra basin in Western Himalayas from 1989 to 2020. The presented approach requires three inputs: annual Equilibrium Line Altitude (ELA), long-term average mass balance, and an estimate of mass balance gradient across ELA for a representative glacier. Here, the annual ELA for each study glaciers is estimated using freely available optical remote sensing images. The average mass balance of the study region and mass balance gradient of a representative glacier are obtained from satellite-based geodetic method and available field estimates, respectively. The obtained results indicate that the average ELA of the basin increased at a rate of 4.22 m asl year⁻¹ during study period. The reconstructed SMB estimates indicate that the glaciers in the Chandra basin were in near-steady state between 1989 and 1999; then, lost mass at an accelerated rate. The basin-wide average SMB for the study period is estimated to be − 0.47 ± 0.50 m w.e. year⁻¹. Overall, Chandra basin lost 13.72 ± 12.5 m w.e (7.3 ± 6.5 Gt) ice mass between 1989 and 2020. Though the estimates have relatively high uncertainty compared to other available studies, the results are encouraging considering the simplicity and parsimonious nature of the approach. Furthermore, a sensitivity analysis shows that reduction in overall uncertainty can be achieved using average mass balance estimates characterized by less uncertainty. Encouraging results suggest that the adopted approach can be extended to other regions. However, detailed studies with proper validation are needed in other regions of Himalayas to ascertain the use of this approach on the unmonitored glaciers of Himalayas to reconstruct time series of annual SMB. [ABSTRACT FROM AUTHOR]