Glacier distribution in the Himalayas and glacier shrinkage from 1963 to 1993 in the Bhutan Himalayas

Himalayan Range extends more than 2,000 km from east to northwest; influence of summer monsoon on glaciers differs regionally. Glacier distribution in the whole Himalayas and terminal/ areal variations of debris-free glaciers in the recent 30 years in Bhutan are analyzed from newly published inventories of India, east Nepal and Bhutan, topographic maps and satellite images. Lowest elevations and estimated equilibrium line altitudes (ELAs) of glaciers in the eastern half of the Himalayas located at the similar latitudes descend toward east from Nepal via Sikkim-Bhutan to Arunachal. The estimated ELAs in the eastern Himalayas at the lower latitudes are not so much different from those in Himachal-Gharwal in the western Himalayas at the higher latitudes, though those descend from Himachal-Gharwal to Kashmir toward north (west). These tendencies of glacier distribution appear, since monsoon precipitation increases toward eastern/southern part from western/northern part in the Range, and the higher precipitation increases accumulation and accompanied cloudy weather decreases ablation. Almost all glaciers measured in the whole Himalayas have been retreating in the recent decades. Averaged annual terminal retreat of glaciers in Bhutan is higher than that in Nepal. An increasing trend of glacier retreat is found in Nepal from west to east, in Nepal and Bhutan from north to south. These tendencies of glacier variation are explained, since glaciers vary more in places with the higher precipitation and the warmer temperature due to mass balance characteristics of the summer-accumulation type glaciers.