Spatiotemporal Variations Of Karakoram Glacier Summer Albedo And Its Causes

The amount of incoming solar radiation energy absorbed by the glacier surface is determined by the surface albedo.Therefore,the role of albedo is very important in modulating the surface energy balance of glaciers.The glaciers and ice caps throughout the world are losing mass rapidly with the passage of time as a response to the global climate change.Just about 3% of the total ice volume on the Earth is represented by the mountain glaciers but have a significant contribution to the sea level rise.The changing dimensions of the glaciers worldwide are expected to leave an impact on the climate and sea level assuring the importance to understand and describe the glacier climate.The primary and most important source of energy heating and becoming a cause of retreating glaciers is absorbed solar radiations.According to the recent studies,the glaciers in the Karakoram are melting due to the climate change and some anthropogenic activities darkening glaciers and becoming a source of glacial retreat.Surface melt of glacier most likely occurs when there is a substantial decrease in the amount of albedo.Several studies in the past have been conducted to estimate the spatial and temporal variation of surface albedo of glaciers around the world.But a very few studies have been conducted to understand the albedo variation on Karakoram glaciers.Therefore,there is need of understanding the spatiotemporal variation of surface albedo(essential for estimating glacial surface melt)for the whole Karakoram region.This work is first comprehensive study of its nature discussing summer albedo of the most important glacier in the region and the Karakoram glacial region of Pakistan as a whole.The main objective of this study is to assess the spatiotemporal variability in surface albedo of the Karakoram glaciers in Pakistan during the summer seasons(June,July and August)for the period from 2000-2018.Moderate Resolution Imaging Spectroradiometer(MODIS)data was used to estimate the amount of glacier surface albedo.MODIS Terra-and Aqua-derived albedo products were combined to reduce the amount of cloud influence and to improve the estimation of glacier surface albedo.The results indicated that the average annual decrease in albedo is ~0.041% during the summer season at Karakoram glacial region as a whole.The decrease in albedo was relatively high during recent years,with an annual rate of decrease of ~0.45%.The variations in the amount of albedo was discussed in details for five largest glaciers in the region.Out of 27 glaciers under study,spatiotemporal variation in summer albedo was highest at Siachen glacier.A negative trend of albedo was observed at Siachen glacier from year 2000 to 2018 with a rate of average 0.25% decrease in albedo per year.A slight trend in decreasing albedo was observed during the last decade(2000-2009)and sharp decreasing trend was observed during the recent years(2010-2018)at Siachen glacier.Albedo difference was observed for Karakoram as a whole as well as for Siachen glacier(the largest glacier in study area)during year 2000 and 2018.About 76.7% of total number of pixels exhibited the decreasing values of albedo where just 18.4% pixel displayed an increasing albedo values with only 4.9% pixels showed no change in albedo at Siachen glacier.A comparison was performed to determine the albedo variation with elevation.It was noticed that the average amount of summer albedo was observed more at higher elevations than lower elevations.Albedo variations discussed in details for some other largest glaciers(Baltoro,Biafo,Hispar and Panmah glacier)in study region along with Siachen glacier.All of these glaciers exhibited a decreasing albedo trend for average summer surface albedo during 2000-18.The decreasing trend in albedo is towards the northwestern part of the Karakoram mountain range with an average rate of about 0.23% decrease in albedo.Some factors involved in decreasing albedo including light-absorbing particles induced by anthropogenic activities along-with climate change is the potential cause of albedo variations in the study area.Albedo has a strong negative correlation with temperature and a strong positive correlation with precipitation.Though the average decrease in the amount of albedo is not very significant in the Karakoram region,considering the recent decreasing trend it is not negligible.More precise studies are required to understand the basic causes of albedo decline in the region.