Estimation of Glacier Mass Balance on a Basin Scale:An Approach Based on Satellite-Derived Snowlines and a Temperature Index Model

Mass balance is an important metric to assess the growth or decline of water stored in a glacier. The Accumulation Area Ratio (AAR) method where mass balance is proportional to AAR has been used to estimate glacier mass balance by several studies in the past. Since field estimates of AAR are not feasible on every glacier, it is usually estimated by identifying the snowline at the end of ablation season as a proxy of Equilibrium Line Altitude (ELA) on satellite images. However, locating ELA on satellite images is challenging due to temporal gaps, cloud cover and fresh snowfall on glaciers. Hence, the highest observed snowline has been traditionally used to estimate AAR, which usually leads to an underestimate of mass loss. To rectify this problem we propose a method to estimate the position of ELA by combining satellite images with in situ meteorological observations and a snowmelt model. The main advantage of this method is that it can be used to estimate the mass balance of individual glaciers and basins. Application of the method to eight glaciers in the Chandra basin, Western Himalaya is found to reduce the bias in mass balance estimates compared to the traditional AAR technique and the modelled estimates are in good agreement with the geodetic method. When applied to 12 selected glaciers in the Chandra basin, the modelled cumulative mass balance is -1.67 ± 0.72 Gt (-0.79 ± 0.34 m w.e. a^-1) during 1999/2000-2008/09. This method can also be used to estimate the future deviations in mass balance using climate change projections of temperature and precipitation.