Retreat rates of debris-covered and debris-free glaciers in the Koshi River Basin, central Himalayas, from 1975 to 2010

Debris-covered glaciers are common in the Himalayas and play a key role in understanding future regional water availability and management. Previous studies of regional glacial changes have often neglected debris-covered glaciers or have mixed them with debris-free glaciers. In this study, we generated a new glacier data set that includes debris-covered and debris-free glaciers to study the glacial surface area change in the Koshi River Basin in the central Himalayas. Long time-series Landsat data were used to extract the glacier boundaries using automatic and manual classification methods. The glacial area decreased by 10.4% from 1975 to 2010 at a rate of 0.30% a(-1), with accelerated melting since 2000 (0.47% a(-1)). Small glaciers melted faster than large glaciers. In terms of distinctive glacier types, debris-free glaciers shrank at a rate of 0.45% a(-1), faster than debris-covered glaciers (0.18% a(-1)), while debris-covered glaciers larger than 5.0 km(2) retreated at a rate faster than debris-free glaciers of the same-sized group. We also studied the potential interactions between 222 supraglacial lakes and debris-covered glaciers. Debris-covered glaciers with glacial lakes melt faster than glaciers without lakes. This study can improve our understanding of the differences in the changes between debris-covered and debris-free glaciers in the central Himalayas and help evaluate water resource changes in the Himalayas.