Long-term mass balance modelling (1986-2018) and climate sensitivity of Siachen Glacier, East Karakoram

摘要

Located in the eastern lap of the Karakoram Range, the Siachen Glacier is the second longest glacier in the non-polar areas of the world. High altitude, extreme climate and frequent military conflicts on this glacier create antagonistic surroundings for conventional field studies. Although recent advancements in geodetic technique have helped in the estimation of Siachen mass budget (MB), these geodetic estimates have been observed only for short time periods ranging 6 to 10 years. Hence, current study presents a comprehensive assessment of the Siachen long-term MB (32 years) based on temperature index (TI) model. Annual surface MB variability was modelled between 1986 and 2018 by forcing daily air temperature and precipitation from multiple ground stations distributed well across accumulation/ablation zone of the glacier. Mean annual temperature lapse rate (LR) was found midway between dry adiabatic and moist adiabatic LRs. Precipitation gradient (PG) was observed remarkably different below and above 4800 m.a.s.l. glacier altitude. Furthermore, snowmelt factor (SMF) was also estimated using snow thickness and positive degree days (PDDs) information over the glacier surface. Model results showed a nearly balanced condition (- 0.02 +/- 0.05 m.w.e./year) during 1986-2006 followed by an accelerated rate of mass loss during 2007-2018 (- 0.11 +/- 0.05 m.w.e./year), thus making the overall condition of Siachen MB negative during the period 1986-2018 (- 0.05 +/- 0.05 m.w.e./year). Comparison of modelled MB was made with few geodetic studies conducted for the Siachen Glacier at different time scales (mainly after year 2000). Further, the sensitivity of the modelled glacier-wide MB was - 0.24 m.w.e./year for a temperature rise by 1 degrees C, while the sensitivity towards 10% increase in precipitation was estimated to be + 0.16 m.w.e./year. A relationship of the annual MB with accumulation area ratio (AAR) and equilibrium line altitude (ELA) was also established for Siachen glacier.