Glacier changes in the Koshi River basin, central Himalaya, from 1976 to 2009, derived from remote-sensing imagery

We use remote-sensing and GIS technologies to monitor glacier changes in the Koshi River basin, central Himalaya. The results indicate that in 2009 there were 2061 glaciers in this region, with a total area of 3225 90.3 km(2). This glacier population is divided into 1290 glaciers, with a total area of 1961 +/- 54.9 km(2), on the north side of the Himalaya (NSH), and 771 glaciers, with a total area of 1264 +/- 35.4 km(2), on the south side of the Himalaya (SSH). From 1976 to 2009, glacier area in the basin decreased by about 19 +/- 5.6% (0.59 +/- 0.17% a(-1)). Glacier reduction was slightly faster on SSH (20.3 +/- 5.6%) than on NSH (18.8 +/- 5.6%). The maximum contribution to glacier area loss came from glaciers within the 1-5 km(2) area interval, which accounted for 32% of total area loss between 1976 and 2009. The number of glaciers in the Koshi River catchment decreased by 145 between 1976 and 2009. Glacier area on SSH decreased at a rate of 6.2 +/- 3.2% (0.68 +/- 0.36% a(-1)), faster than on NSH, where the rate was 2.5 +/- 3.2% (0.27 +/- 0.36% a(-1)) during 2000-09. Based on records from Tingri weather station, we infer that temperature increase and precipitation decrease were the main causes of glacier thinning and retreat during the 1976-2000 period. Glacier retreat during the 2000-09 period appears to be controlled by temperature increase, since precipitation increase over this period did not offset ice losses to surface melting.