Tracing isotopic signatures (δD and δ18O) in precipitation and glacier melt over Chorabari Glacier-Hydroclimatic inferences for the Upper Ganga Basin (UGB), Garhwal Himalaya

Study region: Chorabari Glacier in Upper Ganga Basin, Garhwal Himalaya. Study focus: Authors attempt to characterize the isotopic signatures in different components of the hydrological cycle and decipher the role of summer and winter precipitation on glacier melt using stable isotopes (delta D, delta O-18) coupled with existing hydrometeorological observations during the glacier ablation season (June-September) for the years 2011-2012. New hydrological insights: The isotopic composition of various components of hydrological cycle i.e., precipitation (rainfall and snowfall), glacier surface ice and glacier melt have partly overlapping isotopic ranges. delta 18O, dD and d-excess compositon indicates that precipitation during pre-monsoon (May/June) and post-monsoon (September/October) season have mixing of local moisture with that from westerlies. While during monsoon (June-September) rainfall-runoff contributes to the streamflow with snow and glacier melt. The depletion pattern of snow covered area (SCA) reflected by snow depletion curves (SDC) imply that most of the solid precipitation in the region results from westerlies, while during summers the precipitation from the Indian Summer Monsoon (ISM) is in the form of rainfall over higher altitudes. The isotopic depletion curve (IDC) of meltwater follows the trend of SDC's. The backward wind trajectories for the precipitation events also indicate that the source of winter precipitation is from westerlies while summer precipitation is from ISM. Present day delta 18O, dD and d-excess composition and their climatic interpretation are site and time specific.