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Abstract

Due to limited in-situ observations, the glaciohydrological modelling is challenging in the Himalaya-Karakoram (HK) region. The present study reconstructs the runoffs in the Chandra-Bhaga basin, where a good amount of in-situ data is available. The SPHY (spatial processes in hydrology), a fully distributed high-resolution hydrological model, is applied over 1979-2020 using ERA5 reanalysis, Globcover land use and HiHydrosoil satellite products. The model is calibrated using 5 years (2010-2015) of in-situ catchment-wide runoff at the Chhota Shigri Glacier catchment outlet and validated with the available 6 years (2000-2006) of in-situ basin-wide runoff at the Chandra-Bhaga basin outlet. The modelled mean annual runoff for the Chandra-Bhaga basin is estimated as 57.79 ± 10.4 m3s-1 over 1979-2020. Maximum runoff occurs during summer-monsoon months, with a peak in July (132.74 ± 59.25 m3s-1). Glacier melt and snowmelt from the glacierized basin area, snowmelt from the non-glacierized basin area, rainfall-runoff and baseflow contribute 38%, 28%, 22% and 12%, respectively, to the total runoff at the basin outlet. The most sensitive model parameters are ‘GlacF’, which differentiates between the amount of glacier melt resulting in direct runoff and ‘Tm’, the threshold temperature for melting. The analysis also indicates that the hydrology of the Chandra-Bhaga basin is mainly dominated by summer precipitation. The study, using sufficient amount of in-situ data at the glacier catchment scale provides reliable reconstructed long-term runoffs for the basin.