Abstract We describe a time series of meteorological parameters and surface energy balance components of a seasonal snow cover from an automatic weather station (4863 m a.s.l., 32.28° N, 77.58° E), for a winter season from 1 December 2012 to 30 March 2013, located on a moraine close to the equilibrium line altitude of Chhota Shigri glacier, Himachal Pradesh, India. The analysis shows that for over 80% of the time in winter, the snow surface was at a cooling phase. During late winter however, the surface had some positive residual energy which induced some melt during peak hours of the day. The net all-wave radiation was mostly negative during winter because of the high reflective property of snow and reduced incoming longwave radiation due to low cloud. The sensible heat flux heats the surface at night and enhances the cooling during day. The latent heat flux is always negative, showing that the surface is losing mass through sublimation processes (−0.83 mm w.e./day). A correlation between the energy fluxes and temperature shows a distinct relationship between fluxes. A comparison between the two studies performed on- and off-glacier reveals a significant difference in some parameters. A higher value (−1.08 mm/day) of sublimation rate at 4863 m a.s.l. shows that a large amount of energy available at the surface was used in sublimation processes. A comparatively lower albedo, relative humidity and net longwave radiation and higher latent heat flux, wind speed and net shortwave radiation yield a distinctive surface energy balance, highlighting the need for a large number of stations at different zones to achieve a coherent picture of energy balance in the region.

Abstract High Mountain Asia contains the largest volume of glacier ice outside the polar regions, and contain the headwaters of some of the largest rivers in central Asia. These glaciers are losing mass at a mean rate of between –0.18 and –0.5 m water equivalent per year. While glaciers in the Himalaya are generally shrinking, those in the Karakoram have experienced a slight mass gain. Both changes have occurred in response to rising air temperatures due to Northern Hemisphere climate change. In the westerly influenced Indus catchment, glacier meltwater makes up a large proportion of the hydrological budget, and loss of glacier mass will ultimately lead to a decrease in water supplies. In the monsoon-influenced Ganges and Brahmaputra catchments, the contribution of glacial meltwater is relatively small compared to the Indus, and the decrease in annual water supplies will be less dramatic. Therefore, enhanced glacier melt will increase river flows until the middle of the twenty-first century, but in the longer term, into the latter part of this century, river flows will decline as glaciers shrink. Declining meltwater supplies may be compensated by increases in precipitation, but this could exacerbate the risk of flooding.

Abstract The sensitivity of glacier mass balance (MB) in response to climatic perturbations has made it an important parameter of study from hydrological, climatological and glaciological point of view. To monitor the health of any glacier system, long-term MB observations are required. These observations among Himalayan glaciers are not available consistently and large glaciers are not often monitored for mass balance due to logistical challenges. One such glacier is the Gangotri, situated in the western Himalaya. In the present study an attempt is made to model the MB over the Gangotri glacier, the biggest glacier in the Ganga basin and also the point of origin of the River Ganges. The mass balance of the Gangotri glacier is estimated during the time period 1985–2014 using two different methods: ice-flow velocity; and energy balance modelling using regional model (REMO) outputs and in situ automatic weather station (AWS) data. The geodetic method is used for the nearby Dokriani glacier, where field-based MB measurements are available. MB of Gangotri glacier estimated for 2001–14 using the ice-flow velocity method is −0.92 ± 0.36 m w.e. a −1 ; for 2006–07, MB using AWS and Tropical Rainfall Monitoring Mission (TRMM) data with the energy balance modelling approach is −0.82 m w.e. a −1 ; and for 1985–2005, MB using REMO data with the energy balance modelling approach is −0.98 ± 0.23 m w.e. a −1 . Using the surface velocity method, it is estimated that the glacier lost 9% of its volume during the period 2001–14. The glacier vacated an area of 0.152 km 2 from the snout region, and retreated by 200 m in the last 14 years. MB values estimated for the Gangotri glacier from different methodologies are remarkably close, suggesting them to be suitable methods of MB estimation. TRMM, High Asia Refined (HAR-10) and Asian Precipitation Highly Resolved Observational Data Integration Towards Evaluation of water resources (APHRODITE) data are used to estimate the precipitation over the glacier. The study suggests that the glacier-wide estimation of weather parameters needs to be improved for more accurate estimation of glacier mass balance. Supplementary material: The snow-covered area, for months Jan-Dec, obtained for Gangotri glacier using Landsat data and NDSI (normalized differencing snow index) for year 2014 is available at https://doi.org/10.6084/m9.figshare.c.3888091