Glacier Variations In Response To Climate Change In The Himalaya During 1990-2015

The Himalaya is located in the southwestern margin of the Tibetan Plateau,where modern glaciers are dense.The special geographical location and sensitive natural environment make it an ideal place,so glacier variations in the Himalaya have been a hot topic in the scientific community.Previous studies have focused mainly on individual glaciers or river basins.However,few studies have reported information about glacier area changes,glacier distribution characteristics,and the relationship between glacier variations and climate change for the entire Himalaya.So it is important to add the knowledge about glacier changes in this region that is of central importance for the understanding of the dynamics of glacier changes in different regions,elements and forms.Long-term observations of glacier changes,as well as the relationship between glacier variations and climate change,have been limited because of the large spatial extent and inaccessibility of remote mountainous terrains.With the development of the GIS and RS technology,multi-temporal and multi-spectral data are ideal for the observation and understanding of glacier changes at higher elevations,simultaneously providing detailed information regarding the present state of glaciation.To better understand the variations of glacier in this region,we used the band ratio threshold?TM3/TM5 for the Landsat TM/ETM+and TM4/TM6 for Landsat OLI?to extract glacier outlines in¹990,²000,²010 and²015.After that,we also generated a series of glacier extents and monitored glacier variations in the past 25 years.Besides,the characteristics of glaciers in the Himalaya on the slopes,different regions,elevations,sizes,aspects and forms also were discussed.Variations in glaciers in response to climate change in the Himalaya were investigated.The results are as follows:The total glacier area is 23229.27 km² and 20676.17 km² in 1990 and 2015.The glacier area reduced by 2553.10 km²,with a rate of approximately 0.44%·a^-1 during the period of 1990-2015.The glaciers shrank and this recession has accelerated in the Himalaya over the past 25 years,especially in 2010-2015.Small and steep glaciers are more sensitive to climate change and smaller glaciers have disappeared.Glaciers of the Himalaya are mainly distributed in southern slope and the ice cover area is14451.25 km²,accounting for⁶2.21%of the glacierized area in 1990.The total glacier area reduced by 9.47%in the southern from 1990 to 2015 and the average annual shrinkage rate of the glaciers on the northern slope(0.54%·a^-1)is greater than that on the southern slope(0.38%·a^-1).Glaciers are mainly distributed in the western of the Himalaya.The total ice cover is 11551.69 km²,accounting for 49.73%of the glacierized area in 1999.Ice cover area in the eastern of Himalaya is minimum,which accounts for¹3.31%of the total glacier area in 1990.The glaciers retreated in the different regions of the Himalaya during 1990-2015.The eastern was fast and the middle was slowest.There was a normal distribution between glacier area and elevation.The glaciers were mainly distributed at approximately 4,800⁶,200 m a.s.l.with an area percent of approximately 84%in 1990.The largest glaciers in the area showed the elevation of5,200⁵,600 m a.s.l.in 1990,2000,2010 and 2015.According to the distribution characteristics at different altitudes in the Himalaya,we found that 5,200⁵,600 m a.s.l.may be the turning point about dry and wet,which is the?second major precipitation zones?in the Himalaya.The glaciers shrank in each elevation and the maximum area loss occurred below 4,600 m a.s.l.between 1990 and 2015.The majority of glaciers distributed in 5°²5°.The glaciers retreated in each slope grade and there was a normal distribution between glacier area shrinkage and slopes.The maximum area loss occurred in 25°³0°,where a decrease of 14.18%took place from1990 to 2015.In detail,the glaciers with east,north,northeast and northwestern orientations comprised 58.94%of the total area in 1990,and relatively few glaciers faced south and southwest.The glaciers retreated in all directions and east-,south-,southeast-and southwest-facing glacier diminished faster than others in 1990-2015.The largest number of glaciers is hanging glacier,followed by cirque-valley glacier,valley glacier,cirque glaciers and ice cap.The largest ice cover of glaciers is valley glacier,which accounts for⁵3.33%of the total glacier area in 1990.The average size of valley glaciers is the largest,and hanging glacier is the smallest.Valley glacier is the most important type in the Himalaya and it has the following features:the firn basin is relatively wide and the rear wall is steep,and the aretes and peaks are developed;there are glacial rapids below the accumulation area;there are surface rivers and subglacial rivers in the ablation area and the moraine is relatively developed in glacier tongue.The number of debris-covered glaciers is relatively small in the Himalaya,whereas covers an area of about 44.21%in 1990.Glacier decreased in the debris-covered glaciers and non debris-covered glaciers,and the ice area loss of the non debris-covered glaciers?15.56%?is greater than that the debris-covered glaciers?5.22%?during 1990-2015,which shows that the moraine in the Himalaya can inhibit the ablation of glaciers to some extent.The eastern and the southern slope of the Himalaya are temperate glaciers.The ice coverage and number of the maritime glaciers are greater than the continental glaciers.The two types glaciers shrank over the past 25 years in our study area,and the average annual shrinkage rate of the continental glaciers(0.55%·a^-1)is greater than that the maritime glaciers(0.39%·a^-1).Regardless of the moraine,the result is just the opposite,which also shows that the moraine and the size of glaciers in the Himalaya have an important impact on the annual average rate of glaciers.We analysed the mean annual air temperature and annual precipitation from 1979to 2003 depending on the time lag of 12 years in the Himalaya,and the results are as follows:Glacier variations in response to climate change in the Himalaya:Glacier in the Himalaya retreated from 1990 to 2015 and the total ice cover was reduced by 2553.10km²,accounting for 10.99%of the glacierized area in 1999.Based on the weather grid data,the temperature exhibited an obvious increasing trend between 1979 and 2003and there was a decreasing trend in precipitation at the same time.Therefore,the main climatic driver for glacier shrinkage is probably the increasing temperature and the decreasing precipitation from 1979 to 2003 in our study area.The lag theory suggests that glacier shrinkage will rapidly shrink in the Himalaya in the next few years.APAC varied from 0.38%·a^-1 between 1990 and 2000 to an obviously higher0.71%·a^-1 from 2010 to 2015.Compared with the mean annual air temperature?MAAT?and precipitation from 1979 to 1988,the MAAT increased and annual precipitation seemed to display a decreased pattern between 1999 and 2003,and the glacier retreat in the Himalaya from 2010 to 2015 can be attributed to the considerable increase in air temperature and decrease in annual precipitation.Glacier changes in response to climate variation on the northern and the southern slope of the Himalaya:Glaciers shrank on the northern and the southern slope of the Himalaya.Combined with the weather grid data in the northern and the southern slope of the Himalaya,we found that the glacier retreat in our study area during the period of 1990-2015 can be attributed to the considerable increase in air temperature and decrease in precipitation.Glacier variations in response to climate change in the different regions of the Himalaya:Glaciers area decreased in the different regions of the Himalaya over the past 25 years.There was a good relationship between the glacier area loss and climate change.The increasing temperature and the decreasing precipitation may result in glacier shrinkage in different regions of the Himalaya.In summary,glaciers in the Himalaya and different regions had retreated from1990 to 2015,which may be the result of a combination of increase in air temperature and decrease in precipitation.