Estimation of discharge from Gilgit River Basin,Karakoram Pakistan using a Glacio-hydrological Model

In scarcity of hydro-meteorological and cryospheric data in the mountainous regions, the temperature index model or degree day model often serves as a powerful tool in ice and snow melt computations on a catchment scale. This study uses modified positive-degree day model (MPDDM) to estimate daily discharge of Gilgit River basin (drainage area: 13,471 km2) geographically, extends from 35.80°N, 72.53°E to 36.91°N, 74.70°E, a sub-catchment of upper Indus basin in the high Karakoram region. The main aim of the present study is to estimate the present and future daily discharge from Gilgit River basin using MPDDM. The MPDDM is calibrated for the period 1999-2005 and is validated for the period 2006-2010 with Nash-Sutcliffe values of 0.85 and 0.80 and volume difference of 4.26 % and 3.72 %, respectively. Similarly, the relative contribution of snow and ice melt in the total discharge in the calibration and validation years are 27.71 % and 26.21 %, respectively. The projected discharge of the basin from 2020 to 2099 shows a decreasing trend by -0.008 m3/s per year in RCP4.5 and -0.41 m3/s per year in RCP8.5 with the increase in snow and ice melt contribution of 28.03 % in RCP 4.5 and 28.28 % in RCP 8.5. The results obtained from the MPPDM showed that this model is good enough to estimate daily discharge from glacierized river basins. It can also be used in climate sensitivity studies and in the prediction of future discharge.