Remote Sensing Monitoring Of Glacier Changes In Geladandong From 1999 To 2020

The Geladandong region,Tuotuo River’s source,is the primary source of the Yangtze River;hence,it is an essential ecological protection area in China,which serves as the ecological functional area at the source of the Yangtze River,as well.The Geladandong region is less affected by human activities,and thus is susceptible to climate change.Therefore,it can be regarded as an ideal location for studying regional response mechanisms to global climate change.However,it is difficult to conduct long-term and continuous in-situ measurements for the Geladandong region due to its relative geographical isolation.As a result,there is currently a lack of basic data on glaciers in the Geladandong region.In recent years,remote sensing technology has rapidly developed,effectively for monitoring glacier conditions in isolated regions.Remote sensing technology can significantly improve the accuracy of extracting glacier information and address the lack of long-term observation data on the glacier area and length changes in the Geladandong region.To this end,this study uses Landsat satellite images,China’s second glacier catalog,digital elevation model（DEM）data,and meteorological data,together with the random forest method,to extract annual and interannual glacier boundary information in the Geladandong region 1999 to 2020.On this basis,this study also analyzes the characteristics of glacier changes in terms of glacier area and length changes.Further,it quantitatively evaluates the impacts of climatic,topographic,and glacier size factors on glacier changes.The main conclusions of this paper are as follows:（1）Between 1999 to 2020,the glacier area in the Geladandong region showed an overall retreating trend:the glacier area decreased by a total value of 43.94km2,with a retreating rate of 6.8%and an average annual retreating rate of 2.09km2·a^-1.It is worth noting that the area and the corresponding rate of the glacier retreating from autumn to winter are greater than those from spring to summer.In addition,within the epoch from 2014 to 2020,the glacier retreating area and rate are higher than those from 1999 to 2004,and so does the average annual rate of the glacier retreating.However,glacier change is not a one-way process;it involves advancing and retreating.In over twenty years,from 1999 to 2020,the glacier retreating area was50.23km2while the glacier advancing area was 6.29km2.（2）In the past 20 years,the lengths of the glaciers in the Geladandong region have shown continuous shrinking trends both annually and interannually.Specifically,the total glacier length has decreased by 30.52km,with a shrinkage rate of 8.7%and an average annual shrinkage rate of 1.45km·a^-1.The results also show that the glacier lengths are highest in autumn.Besides,the standard deviation of the glacier lengths is the smallest in summer,indicating that the glacier is more stable in summer.Additionally,the glacier shrinkage length and rate from autumn to winter are much greater than those from spring to summer.Furthermore,within the period from 2014 to 2020,the glacier’s shrinkage length and rate are relatively higher than the period from 1999 to 2004,and the average annual shrinkage rate of the glacier exhibited a similar tendency.（3）The climate was the primary factor in affecting the glacier changes,wherein the temperature was the main driving force behind the retreating of glacier area and length.At the same time,the precipitation showed a relatively weaker influence.Conversely,the topographic condition and glacier size could also impact on the glacier changes.Results suggest that the glacier area gradually increases between 5200-5800m above the geoid,and it decreases between5800-6600m above the geoid.Additionally,the glacier area decreases with the increasing slope,and this phenomenon is more pronounced on the north-facing slopes compared to the south-facing slopes.Furthermore,results indicate that the larger the glacier size,the fewer the number of glaciers,the longer their average length,and the slower their retreating rate.In conclusion,using remote sensing technology to monitor the long-time series of glacier changes in the Geladandong region not only has important practical significance for the study of the regional response mechanism of global climate change but also has a greater reference value for the management of water resources quantity in the region and the social development of the downstream region.