Remote sensing monitoring of glacier changes on the northern slope of the middle Himalayas from 1990 to 2020
As one of the centers of glaciation in the mid-latitude region,the Himalayas are closely related to the climate environment in terms of their changing spatial and temporal pattern characteristics.Based on Landsat series remote sensing images,this study analyzes the distribution and variation characteristics of glaciers on the northern slope of the middle Himalayas from 1990 to 2020 by using ratio threshold and visual interpretation methods.The results showed that:(1)In 2020,the glacier area in the study area decreased to 2763.72 km2,a change of 622.35 km2 compared with 1990,and the glacier continued to retreat with a rate of 0.61％/a.(2)From the perspective of topographic characteristics,the area of glaciers showed a normal distribution trend with altitude,and the most significant area of glacier retreat was concentrated at 5500-6000 m,with a retreat area of 321.03 km2.In the range of 3500-4000 m,the average annual retreat rate of glaciers was the largest,which was 1.12％/a.(3)The distribution area of non-surface moraine glaciers in the study area is much higher than that of surface moraine covered glaciers,and the retreat rate of the former(0.78％/a)is much greater than that of the latter(0.31％/a),indicating that the surface moraines in the study area have a certain degree of inhibition on glacier melting.(4)In 2020,the valley glaciers in the study area had the largest distribution area of 1649.63 km2,followed by hanging glaciers,cirque-valley glaciers and cirque glaciers with an area of 574.71 km2,429.39 km2 and 105.59 km2,respectively,while the flat-topped glaciers had the smallest distribution area of only 2.40 km2.(5)It is worth noting that more than half of the glacier surface in the valley glaciers is covered by moraines,while no surface moraine cover glaciers are found in flat-topped glaciers.Different types of glaciers are affected by surface moraine cover to different degrees,and in general,the degree of bare ice retreat is more intense,and the average annual retreat rate of hanging glaciers is the largest in the surface moraine cover area,reaching 1.04％/a.
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