Assessment and Simulation of Glacial Lake Outburst Floods for Dhauliganga Basin in Northwestern Himalayan Region

Abstract

Satellite based remote sensing is a convenient tool for the study of cryosphere that allows to carry out investigations over large and inaccessible areas. The present investigation has been carried out to monitor seasonal variation in the Snow Cover Area (SCA) for the upper Bhangirathi basin, located in the Garhwal region of Indian Himalaya. This analysis has been done using Moderate-Resolution Imaging Spectroradiometer (MODIS) satellite data for the past 11 years (2000– 2010); the temporal snow cover being derived using the Normalized Difference Snow Index (NDSI). The entire study basin has been divided into nine elevation zones, on the basis of Digital Elevation Model (DEM), for estimating the SCA for each zone. Zones 1–9 cover different elevation ranges: (1) above 6,500 m, (2) between 6,000 and 6500 m, (3) 5,500–6000 m, (4) 5,000–5500 m, (5) 4,500– 5000 m, (6) 4,000–4500 m, (7) 3,500–4000 m, (8) 3,000–3500 m, and (9) below 3,000 m. Mann Kendall and linear regression methods have been employed to iden- tify trends in the SCA during the period 2000–2010. The snow cover depletion analysis depicts a shift in the duration of ablation and accumulation during the study period in the basin. The analysis indicated 13–21 % increase in SCA in the middle elevation zones (4 and 5) and 2–9 % decline in SCA in the lower elevation zones during autumn. SCA was found to increase across all the elevation zones in win- ter; the rate of increase was particularly high (14–21 %) in the lower elevation zones as compared to higher (2–3 %) and middle elevation zones (4–10 %). Similarly, an increase of 2–3 % in the higher elevation zones, 6–14 % increase in the mid- dle elevation zones and 2–6 % decline in the lower elevation zones was observed in respect of SCA during spring. However, no significant variation in SCA was observed during the summer season. Decadal variation in SCA showed mean annual increase of 8–15 % in the middle elevation zones (3–5). In the lower elevation zones (<4,500 m), mean annual SCA showed increase of 11–14 % between 2000 and 2005, followed by 6–8 % decrease in the upper Bhagirathi Basin.