Variations in glacial area in the middle Himalayas over the past 30 years

As an integral part of the Asian water tower, the spatiotemporal characteristics of Himalayan glaciers are closely linked to climate and the environment. Using Landsat TM/ETM+/OLI image data, the distributions of and changes in glacial areas in the middle Himalayas from 1990 to 2020 were extracted and analysed through the ratio threshold method and manual visual interpretation. The findings revealed a retreat of glaciers over the past 30 years, with the glacial area decreasing from 8584.75 km2 in 1990 to 7210.79 km2 in 2020, indicating a reduction of 1373.97 km2 (16.00%) and an average annual retreat rate of 0.53%. Debris-covered glaciers and debris-free glaciers show similar proportions in the study area, but the former exhibit a significantly lower annual retreat rate (-0.30%) than the latter (-0.78%), suggesting that moraine may impede glacier retreat. Glacial morphology encompasses valley glaciers, hanging glaciers, cirque glaciers, cirque valley glaciers, and flat-topped glaciers. Among these glaciers, valley glaciers constitute the primary glacier type in the study area, accounting for approximately 50% of the total area, whereas flat-top glaciers are the least common. Moraines associated with valley glaciers are relatively developed; debris-covered glaciers represent 75.74% of this glacier type, whereas flat-topped glaciers are entirely debris-free.