• Wahid, Shahriar
• Zheng, Hongxing
• Neumann, Luis
• Nepal, Santosh
• Chen, Jie

Abstract

Snow and glacial melt processes are an important part of the Himalayan water balance. However, quantification of melt runoff depends upon data availability and conceptualization of hydrological models applied. This paper describes in detail an application of conceptual GR4J hydrological model in the Tamor catchment in Eastern Nepal using typical elevation band and degree-day factor approaches to handle Himalayan snow and glacial melt processes. The paper contributes a model conceptualization (GR4JSG) that enables coarse evaluation of modeled snow extents against remotely sensed MODIS snow extent. Novel aspects include the glacial store in GR4JSG and examination of how the parameters controlling snow and glacial stores correlate with existing parameters of GR4J.The model is calibrated using a Bayesian Monte Carlo Markov Chain method against observed streamflow for one glaciated catchment with reliable data. Evaluation of the modelled streamflow with observed streamflow gave Nash Sutcliffe Efficiency of 0.88 and Percent Bias of <4%. Evaluation of the modelled snow extents with MODIS gave R2 (coefficient of determination) of 0.46, with calibration against streamflow only (i.e.without reference to snow extent in calibration). The contribution of melt runoff from the catchment is 15% (including 6% from glacier area).The model is highly sensitive to rainfall and temperature data, which suffer from known problems and biases, for example due to stations being located predominantly in valleys and at lower elevations. Testing of the model in other Himalayan catchments may reveal additional limitations.

Topics

• impedance spectroscopy
• melt