Glacio-hydrological degree-day model (gdm) useful for the himalayan river basins

Abstract

This chapter describes a Glacio-hydrological Degree-day Model (GDM) which uses degree-day factors for estimating snow and ice melt that calculates total discharge from a river. It is a physically based gridded glacio-hydrological model which is useful for the Himalayan river basins. The GDM is successfully used in the Marsyangdi River basin (MRB) and Trishuli River basin (TRB). The model is first calibrated and validated by using observed discharge over the period of 2004–2014. A long-term continuous simulation is then carried out for 2020–2100 in both basins. Results show that the model simulations are good. The Nash-Sutcliffe Efficiency (NSE) are 0.79 and 0.83 for the period of 2004–2007 in MRB and from 2007 to 2010 in TRB, respectively during the calibration period and 0.81 and 0.76, for the period of 2008–2010 in MRB and from 2011 to 2014 in TRB, respectively. The snow melt and ice melt contributions to total discharge in MRB are 15% and 13%, respectively whereas 12% and 16% in TRB for the calibration period. The Representative Concentration Pathways (RCPs) 4.5 W m−2 scenario for the period of 2020–2100 shows an average increase of simulated discharge by 1.43 m3 s−1 per year and 0.25 m3 s−1 per year for MRB and TRB, respectively. Similarly, in RCP 8.5 the discharge increases by 0.71 m3/s per year and 0.94 m3 s−1 per year in MRB and TRB, respectively. The model can be used as a promising tool for the study of hydrological system dynamics and potential impacts of climate change on the Himalayan river basins.