Assessment of runoff components using glacio-hydrological model

Abstract

This study evaluated the runoff components—snow, ice, and rainfall runoff—in the Gangotri glacier system using a glacio-hydrological model from 1980 to 2020. The model was driven using bias-corrected ERA5 reanalysis data for daily air temperature and precipitation extracted from the nearest grid to the Bhojbasa meteorological station. The model was calibrated to get the suitable threshold temperature for melt (Tm) and precipitation gradient (Pg) by minimizing the root mean square error (RMSE) between the available in-situ and modelled runoff for the year 2000-2002, and the model was validated against the available in situ daily runoff data for the year 2003. The study revealed significant interannual variability in runoff, ranging from a minimum of 24.3 m3/s in 1989 to a maximum of 33.34 m3/s in 1994, while the mean annual runoff was 29.27 m3/s over the period 1980-2020. Ice runoff was observed as the primary contributor to the total mean annual runoff, with a 52% contribution, followed by the snow runoff and rainfall contribution of about 36% and 12%, respectively, over the whole period. The pre- and post-2000 period runoff was also estimated to check the impact of increased temperature post-2000, and the increment in runoff was found to be 0.49. The study revealed distinct trends across different temporal intervals because of the various climate variability, highlighting the importance of continuous long-term monitoring to understand the glacier-climate interaction.