Assessment of the hydrological components in the glacierized Dudh Koshi river catchment (Nepal)

International audienceThe Himalayan water resources, vital for 800 million people, come mainly from the monsoon and from the melting of the cryosphere. The impact of climate change on these resources, especially on the cryosphere, is a major issue in the Himalayan range. In this context, assessment of the rainfall, snowmelt and ice-melt components of the water balance is crucial. Consequently, a distributed conceptual hydrological model (HDSM) was developed to estimate the contribution of each component to the Dudh Koshi river flow from 2001 to 2005. The Dudh Koshi river basin (3700 km2), with 14% of glacierized area and Mount Everest as the highest peak, is located in eastern Nepal. The snow-cover area, calibrated with satellite data (MOD10A2), and the daily runoff are correctly simulated by the model. Nevertheless, to obtain these results the ice degree-day factor is overestimated (~36 mm °C–1 d–1), leading to an ice-melt contribution around 60% of annual discharge, against 5% in the literature. This overestimation offsets underestimation around 80% of precipitation, especially solid precipitation. After correction of the precipitation, the contributions of rainfall, snowmelt and ice melt represent, respectively, 63%, 9% and 29% of the Dudh Koshi annual discharge from 2001 to 2005. These results highlight large uncertainties in the hydro-climatic data of the Dudh Koshi river basin, which limit understanding of the hydrological and cryospheric processes. They also underline the limited influence of the glacier melting in the context of climate change on the annual Dudh Koshi river’s water resources, since the monsoon rainfall is the main component of the flow