Glacier changes in the Garhwal Himalaya, India, from 1968 to 2006 based on remote sensing

Glacier outlines are mapped for the upper Bhagirathi and Saraswati/Alaknanda basins of the Garhwal Himalaya using Corona and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite images acquired in 1968 and 2006, respectively. A subset of glaciers was also mapped using Landsat TM images acquired in 1990. Glacier area decreased from 599.9 +/- 15.6 km(2) (1968) to 572.5 +/- 18.0 km(2) (2006), a loss of 4.6 +/- 2.8%. Glaciers in the Saraswati/Alaknanda basin and upper Bhagirathi basin lost 18.4 +/- 9.0 km(2) (5.7 +/- 2.7%) and 9.0 +/- 7.7 km(2) (3.3 +/- 2.8%), respectively, from 1968 to 2006. Garhwal Himalayan glacier retreat rates are lower than previously reported. More recently (1990-2006), recession rates have increased. The number of glaciers in the study region increased from 82 in 1968 to 88 in 2006 due to fragmentation of glaciers. Smaller glaciers (<1 km(2)) lost 19.4 +/- 2.5% (0.51 +/- 0.07% a(-1)) of their ice, significantly more than for larger glaciers (>50 km(2)) which lost 2.8 +/- 2.7% (0.074 +/- 0.071% a(-1)). From 1968 to 2006, the debris-covered glacier area increased by 17.8 +/- 3.1% (0.46 +/- 0.08% a(-1)) in the Saraswati/Alaknanda basin and 11.8 +/- 3.0% (0.31 +/- 0.08% a(-1)) in the upper Bhagirathi basin. Climate records from Mukhim (similar to 1900 m a.s.l.) and Bhojbasa (similar to 3780 m a.s.l.) meteorological stations were used to analyze climate conditions and trends, but the data are too limited to make firm conclusions regarding glacier-climate interactions.