Using Landsat images to monitor changes in the snow-covered area of selected glaciers in northern Pakistan

Landsat satellite images were used to map and monitor the snow-covered areas of four glaciers with different aspects (Passu: 36.473°N,74.766°E; Momhil: 36.394°N,75.085°E; Trivor: 36.249°N,74.968°E; and Kunyang: 36.083°N,75.288°E) in the upper Indus basin,northern Pakistan,from 1990-2014. The snow-covered areas of the selected glaciers were identified and classified using supervised and rule-based image analysis techniques in three different seasons. Accuracy assessment of the classified images indicated that the supervised classification technique performed slightly better than the rule-based technique. Snow-covered areas on the selected glaciers were generally reduced during the study period but at different rates. Glaciers reached maximum areal snow coverage in winter and pre-monsoon seasons and minimum areal snow coverage in monsoon seasons,with the lowest snow-covered area occurring in August and September. The snow-covered area on Passu glacier decreased by 24.50%,3.15% and 11.25% in the pre-monsoon,monsoon and post-monsoon seasons,respectively. Similarly,the other three glaciers showed notable decreases in snow-covered area during the pre- and post-monsoon seasons; however,no clear changes were observed during monsoon seasons. During pre-monsoon seasons,the eastward-facing glacier lost comparatively more snow-covered area than the westward-facing glacier. The average seasonal glacier surface temperature calculated from the Landsat thermal band showed negative correlations of -0.67,-0.89,-0.75 and -0.77 with the average seasonal snow-covered areas of the Passu,Momhil,Trivor and Kunyang glaciers,respectively,during pre-monsoon seasons. Similarly,the air temperature collected from a nearby meteorological station showed an increasing trend,indicating that the snow-covered area reduction in the region was largely due to climate warming.