SNOWMELT RUNOFF MODELING IN CHENAB BASIN USING REMOTE SENSING AND GIS

Abstract

Snow is a great resource for water particularly for Himalayan Rivers. Although seasonal snow cover is an important parameter in the hydrological regime of a basin, its contribution is confined to the spring season when snow-melt and base--flow constitute two components of the discharge. Once the, summer sets in, it is the exposed . glacier ice in the ablation zone which is the main contributor to the melt along with monsoon rainfall. The present study is primarily carried out for assessment of streamflow in the Chenab River up to Premnagar. In the study Terra MODIS satellite data has been used for mapping the snow cover area (SCA). The lapse rate has been estimated using the LST maps generated from the thermal bands of -the satellite data.. A methodology to produce daily SCA directly from Terra MODIS snows 'cover map products (MOD1OA1) is presented. The study catchment is divided into nine elevation zones and snow cover has been -computed for these elevation zones using MODIS data. On the basis of SCA, snow cover depletion curves have been prepared. The Snow cover depletion curves vary significantly from year to year. It was observed that the snowmelt starts in the month of March while after August snow cover accumulation starts. The upper part of the basin remains snow covered and lower part remains snow free throughout the year. Snow covered area varies between 10%. and 80% in the whole basin depending on time of the year. Study reveals that there exits an inverse linear correlation between LST and elevation. Using this property, the lapse rate for different seasons has been computed. ix Simulation has been carried out taking snow cover area, lapse rate and meteorological data using snowmelt- runoff model. Available data of five years was split into two parts; one "is' used for calibration purpose (2000-01, 2001-02, 2002-03) and the remaining- data of two years (2003-2004, 2004-2005) for model validation. During calibration period, it is noticed that for all the three years the daily discharge simulated with ,efficiency ranging from 0.84 to 0.92 and difference in volume ranging from 1.57%o to 7.26%, which indicates good to very good perfonnance of the model for all the years. The calibrated model was appliedto independent data set for years 2003-2004 and 2004-2005 to check the applicability of the model. The model could reproduce independent data sets with efficiency- between 0.81-0.91 comparable to that, of calibration period indicating applicability of the model to simulate runoff in study basin. The seasonal distribution of strearnflow indicates that about 60% of annual flows are generated during the summer season and about 75% of this summer flow is obtained from snowmelt. SNOWMOD, a temperature index based runoff model worked well in the study basin with limited data. Such estimates are useful for planning and management in this-basin. x