Introduction:
The Himalayas-Karakoram-Hindu-Kush (HKH) region hosts multiple extended glaciers (Kaab et al. 2012). The Karakoram Range, situated in the upper Indus basin, has an extensive formation of glaciers due to its high altitude (Young et al. 1990). The eastern and northwestern Himalayas are seasonally snow covered; however, the snow-cover extent of the central Himalayas is relatively limited (Menegoz et al. 2013b). Glaciers located in this region are an important source of freshwater for China, Pakistan, Nepal and India. Glaciers are also good indicators of climate change, and a minor climate variation, such as temperature change, can produce a rapid glacial response (e.g., Vuille et al. 2008a; Soruco et al. 2009; IPCC, 2013; Rabatel et al. 2013). The snow-covered area on a glacier affects water balance determination and radiation, which are important components in climate studies and the hydrological cycle (e.g., Cohen et al. 2001; Stieglitz et al. 2001).
The extent, thickness and melt rate of snow-covered areas depend on geographical location, elevation, season, solar irradiance, and atmospheric pollutant concentrations and deposition on the snow surface (Kopacz et al. 2011; Menegoz et al. 2014). In the Himalayas region, the largest snow extent occurs in the elevation zone between 3000 and 6000 m (Maskey et al. 2011). Glaciers in many parts of the world, such as those in the tropical Andes, are currently retreating, similar to those in polar regions (Bradley et al. 2006; Vuille et al. 2008a; IPCC, 2013; Rabatel et al. 2013). Glacier shrinkage has also been prevailing over the Third Pole region (e.g., Donghui et al. 2007; Kang et al. 2010; Fujita et al. 2011; Kaab et al. 2012; Bolch et al. 2012; Yao et al. 2012; Neckel et al. 2014; Kang et al. 2015). Negative mass balance was also confirmed from in situ stake observations during the last decade for the Tibetan Plateau and Urumqi glacier no. 1 of the Tianshan Mountains (Yao et al. 2012; Zhang et al. 2014). Snow deposition and loss are primarily controlled by the atmospheric condition and state of the land surface. Anthropogenic pollutants, such as black carbon deposited on snow, were found to shorten the snow cover season in the Northern Hemisphere (Ménégoz et al. 2013a). In the central Himalayas, it was estimated that the deposition of atmospheric pollution on snow could reduce the snow cover season at the rate of 8 days per year. It was also observed that depositions of black carbon on snow contribute significantly to the decrease in snow cover extent (Dery et al. 2007). Regional temperature variation, solar energy flux and precipitation are the main factors that affect a glacier’s mass balance (Pouyaud et al. 1997; Francou et al. 1998). It is expected that the present retreating behavior of glaciers will continue in the future (Oerlemans et al. 1998; Shi et al. 2000). Similarly, it has been found that both snow melt and snowfall were strongly influenced by even minor temperature increases (US EPA CCD Snow and Ice).
Changes in the snow-covered area of selected glaciers:
Snow-covered areas of four glaciers with different aspects (Passu: 36.473°N, 74.766°E; Mumhil: 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 four different seasons. Snow-covered areas on the selected glaciers were generally reduced 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, Mumhil, 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.
GCISC References:
Gul C, Shaukat Ali. et al (2017): Using Landsat images to monitor changes in the snow-covered area of selected glaciers in northern Pakistan. Journal of Mountain Science (Accepted)
Khan, F., Pilz, J., & Shaukat Ali. (2017). Improved hydrological projections and reservoir management in the Upper Indus Basin under the changing climate. Water and Environment Journal.
Mountain Research Initiative EDW Working Group. Muhammad Zia ur Rahman Hashmi (2015). Elevation-dependent warming in mountain regions of the world. Nature Climate Change, 5(5), 424-430.
Shaukat Ali, Li, D., Congbin, F., & Khan, F. (2015). Twenty first century climatic and hydrological changes over Upper Indus Basin of Himalayan region of Pakistan. Environmental Research Letters, 10(1), 014007.
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