20. Snow Cover Dynamics and Timberline Change Detection of Yamunotri Watershed Using Multi-temporal Satellite Imagery

This paper is an attempt to examine the impact of climate change over snow cover and timberline dynamics in the alpine zone of Yamunotri watershed in the Garhwal Himalaya. The study extracts dynamics of snowline and timberline using Landsat TM data of two different time periods, i.e. 1990 and 2010. Temporal images of study area were processed in the GIS environment using Normalized Difference Snow Index (NDSI) and Normalized Difference Vegetation Index (NDVI) algorithm on ERDAS Imagine and ArcGIS 9.3. To determine the height of the snow and timberline, Shuttle Radar Topographic Mission (SRTM) data was used. The result reveals that the snow cover in 1990 was estimated at 707 km² which decreased to 552 km² in 2010. The average height of timberline in Yamunotri watershed was 3580 m in the year 1990 and 3660 m in 2010, while the average height of snowline was 4480 m in 1990 and 4660 m in 2010. These data suggest that due to global warming the timberline in the alpine zone has been shifted towards higher elevation at an average rate of 4 m/year during the last 20 years (i.e. 1990–2010). The snowline has also shifted towards higher elevation at an average rate of 9 m/year. During this period, about 68.58 km² non-timber areas of the alpine zone were converted into timber area at an average rate of 3.42 km²/year, while during the same period, about 155 km² snow cover areas were converted into non-snow cover area at an average rate of 7.75 km²/year.