Spatial-temporal Changes Of Glacier Thickness And Lake Level On The Qinghai-tibetan Plateau

The Qinghai-Tibetan Plateau,known as “water tower of Asia”,is the largest modern glacier area outside the Poles.It contains about 29.2% of ice volume in Asia,81.6% of ice volume in China and approximately has more than 1091 lakes.It is the origin of several big rivers in Asia such as Brahmaputra,Ganges,Indus,Mekong,Salween,Yellow River and Yangtze.However,recent studies showed that the glaciers on the Qinghai-Tibetan Plateau have been retreating significantly which influences the lake level and water storage change in this region.Therefore,it is essential to study the changes of the glacier and the lake.ICESat(Ice,Cloud,and land Elevation SATellite)is part of NASA's Earth Observation System(EOS),which was launched in January 13 in 2003 for measuring ice sheet mass balance,cloud and aerosol heights,as well as land topography and vegetation characteristics.It provides multi-year high accurate global elevation with small size of footprint and was used to extract glacier thickness change and lake level change in many previous studies.In this thesis,the plane fitting method,originally used for glacier thickness change extraction and applicable to flat ice sheet condition using ICESat elevation data,was improved.The improved method uses surface equation instead of plane equation to derive difference equation algorithm,which can reduce the error caused by the deviation between the fitted surface and the real glacier surface.Besides,the elevation changes from 2003 to 2009 of the glacier and the lake were extracted by combining ICESat elevation data and SRTM DEM with 30 meter resolution.Under the condition of 90% confidence,results of 154 glacier thickness change and results of 111 lakes levels changes were acquired.The results showed that glacier thickness in the southern part of the Tibetan plateau is decreasing significantly while the northern part is stable or slightly increasing;most of the lake levels in the inner plateau showed an increasing trend except the lake level in the Brahmaputra basin showed slightly decreasing trend.The HydroSHEDS basin data was used to establish the relationship between lakes and glaciers within the lake upper basin.The elevation changes of lake and corresponding glacier thickness were analyzed.Three different patterns of relationship between lake level and glacier thickness were found in 42 pairs of lakes and glaciers.Precipitation,Evapotranspiration and Temperature data were used to explore the causes of forming the three patterns.For the first patterns,lake level and the thickness of corresponding glaciers are increasing.These lakes and glaciers are distributed along Kunlun Mountains and the increasing of the lake level is mainly influenced by precipitation.For the Second patterns,glacier thickness is decreasing while the lake level is increasing.These lakes are distributed on the source region of the Yangtze River,the Yellow River and the Lancang River.The increasing trend of the lake level are mainly caused by the increasing of precipitation and corresponding glacier meltwater.For the third patterns,both glacier thickness and lake level are decreasing.These lakes are distributed along Gangdisi mountains and Himalayas mountains.The decreasing trend of the lake level is mainly influenced by precipitation and the magnitude of decreasing is reduced by the increasing glacier meltwater.