Glacio-hydrological Modeling in the Glacierized Tamor River Basin, Eastern Nepal using Temperature Index Melt Approach.

Abstract:

In the region with sparse hydro-meteorological data, use of temperature index melt model to estimate snow and ice melt has shown to be an effective method to melt modeling. This study presents the estimation of daily discharge of Tamor River basin located in eastern Nepal with relative contribution of snow and ice melt using this approach, which is based on the relation that the melting of snow or ice during any particular period is proportional to the positive temperature linked by positive degree day factor. The study basin is one of the sub-basins of Koshi River basin that lies in the Himalayan region and has an area of 4001.2 km² with approximately 9.4 % of the total basin covered by glaciers (debris covered and clean ice type) and approximately 21.5 % of the area lying above 5000 m a.s.l. The model is calibrated from 2001 to 2005 and validated from 2007 to 2010. The model efficiency assessments show good results with Nash – Sutcliffe model efficiency coefficients and volume differences as 0.80 and 4.8 %, respectively in calibration and 0.83 and 1.1 %, respectively in validation periods. The average discharges during these periods are 237.95 m³/s and 231.49 m³/s with 43.3 % and 40.7 % of average snow and ice melt contributions, respectively. The model is also used to project river discharge from 2020 to 2050 with meteorological input data (i.e., temperature and precipitation) projected from Regional Climate Model using Weather Research and Forecasting (V3.5) model of 12 km resolution and boundary conditions from NorESM, which is bias corrected to the basin scale for RCP 4.5 and 8.5 climate scenarios. The model projection shows increase in river discharge by 0.24 m³/s per year with decreasing snow and ice contribution by 0.03 m³/s per year under RCP 4.5 scenario, whereas it shows decrease in total river discharge and snow and ice contribution as well by 0.29 m³/s and 0.28 m³/s per year, respectively under RCP 8.5 scenario. The study indicates that this model can provide valuable insights into the glacio-hydrological study, especially in the Himalayan regions with less input data and can be very useful tool for present and future water resource management.