Topographic and climatic influence on seasonal snow cover: Implications for the hydrology of ungauged Himalayan basins, India

Himalayan glaciers exert considerable influence on basin hydrology and its response to climate change. Melt-runoff generated from ungauged Himalayan basins (UHB) requires an understanding of snow and ice cover extent along with prevailing meteorological conditions. Therefore, an estimation of seasonal snow cover distribution, topographic (elevation, aspect, and slope) and climatic variability was carried out using satellite data and meteorological observations from three automatic weather stations (AWSs) located at different elevations in an UHB (Chorabari Glacier). Results suggest that the topography and the meteorological conditions of the basin influence the dynamics of snow cover and the corresponding processes responsible for the melt-runoff generation. The snow cover area (SCA) has high variability in the elevation range of 3799–5000 m, indicating that as glacier ablation begins, SCA below this elevation primarily contributes to the melt-runoff. Likewise, the eastern aspect and the slopes (0–10° and 70–80°) show higher variability. Further, the annual distribution of air temperature gradients (dT/dZ) or temperature lapse rates (TLRs) exhibits a bimodal pattern. The mean annual TLR for the basin is 6.0 °C km−1, which is lower than the traditionally used adiabatic or environmental lapse rate (6.5 °C km−1). We also established the role of TLRs in the dynamics of SCA, which is an important parameter used for the computation of melt-runoff. The 0 °C isotherm established indicates that the elevation zone above 5000–5500 m has persistent snow cover throughout the year and snow cover below this zone contributes to the melt-runoff during the ablation season. Therefore, validating the equilibrium line altitude (ELA) of Chorabari Glacier lies within this zone. Since the TLR and SCA vary with space and time, our study in an ungauged glacierized basin of river Ganga could be useful for policymakers as well as other researchers working on the regional hydrology

Boost glacier monitoring

Glacier-mass changes are a reliable indicator of climate change. On behalf of the worldwide network of glacier observers, we urge parties to the United Nations Framework Convention on Climate Change to boost international cooperation in monitoring these changes, and to include the results in the Paris agreement’s global stocktake. Since 1960, glaciers have lost more than 9,000 gigatonnes of ice worldwide — the equivalent of a 20-metre-thick layer with the area of Spain. This melting alone — as distinct from that of the Greenland and Antarctic ice sheets — has raised global sea level by almost 3 centimetres, contributing 25–30% of the total rise (M. Zemp et al. Nature 568, 382–386; 2019). The present rate of melting is unprecedented. Several mountain ranges are likely to lose most of their glaciers this century. And we face the loss of almost all glaciers by 2300 (B. Marzeion et al. Cryosph. 6, 1295–1322; 2012). Glacier shrinkage will severely affect freshwater availability and increase the risk of local geohazards. Global sea-level rise will result in the displacement of millions of people in coastal regions and in the loss of life, livelihoods and cultural- heritage sites. The systematic monitoring of glaciers has been internationally coordinated for 125 years. Continuing to do so will document progress in limiting climate change for current and future generations