Lake Area Dynamics Monitoring On The Endorheic Tibetan Plateau Based On Multi-Source Satellite Data

Monitoring the alpine lake dynamics on the endorheic Tibetan Plateau is vitally important in understanding climate impacts on hydrological cycle.Existing studies have revealed an accelerated lake expansion on the Tibetan Plateau during the 2000 s compared with prior decades.However,the partial hiatus of recent Landsat archive affected the continuation of understanding the lake changes in the recent decade.Here,we synergistically used imagery from Landsat and HJ-1A/1B satellites to enable a detailed monitoring of lake area dynamics on the endorheic Tibetan Plateau from 2009 to 2014.Based on a semi-automatic lake extract method,this study monitored lakes larger than 1.0 square kilometers inter-annually and analyzed the spatiotemporal characteristics of lake area dynamics.In addition,we selected 24 typical lakes in the four sub-region to study the intraannual variability of Tibetan lake areas.The study classified all of the lakes based on three different methods,and studied the dynamics of endorheic and exorheic lakes,the saline and freshwater lakes,as well as the glacier-fed lakes and non-glacier-fed lakes,which can be served as fundamental materials for the evaluation of ecosystem and monitoring of resource and environment.What's more,it is also very significant to the rational development and utilization of water resources on the Tibetan Plateau.At the end of the thesis,we discussed the correlation between lake area dynamics with the changing trend of precipitation and temperature in each basin.The main conclusion of the thesis are as follows:(1)There are 874 lakes larger than 1.0 km2 on the endorheic Tibetan Plateau during 2009-2014,with an average of six year's total area of 32,236.11 km2.The surface area of lakes experienced a significant expansion with an overall rate of 340.79 km2yr-1(1.06% yr-1,P<0.05)and the speed of lake expansion trend has slowed down during the study period.The majority of the lakes in the northwest of the study area shown a rapid expansion,with an annual rate more than 2.0 %yr-1.The lakes located in the middle of the study area are mainly expanding,but some of them are shrinking.Stabilized lakes(the changing rate between-0.5 %yr-1 and 0.5 %yr-1)are mainly distributed in the northern foothills of the southern part of the study area.(2)Changes in endorheic(terminal)lakes contribute to 98% of the net expansion,suggesting that monitoring endorheic lake dynamics is of critical importance for understanding climate changes.Meanwhile,changes in saline lakes,which are mostly endorheic account for 96% of the net expansion,implying that the proportion of freshwater storage on the Changtang Plateau is likely in decline.Rapid expansion occurred in both glacier-fed and non-glacier-fed lakes,with a rate of 224.94 km2yr-1(0.92 % yr-1,p<0.05)and 115.85 km2yr-1(1.47 %yr-1,p=0.08),respectively,indicating that glacier retreat alone may not fully explain the recent lake expansion.(3)Intra-annual variations of the selected 24 large lakes fluctuated within 0.22–2.46%(in coefficient of variation)for glacier-fed lakes and 0.17–2.36% for non-glacierfed lakes.Most of these lakes expanded during the unfrozen period(from May/June to October)and reached to their maximum extents in September or October.(4)By spatially associating our revealed lake changes with climate variables,we observed that the recent lake expansion is more related to precipitation than to temperature,although future efforts are needed for a more comprehensive picture of the lake changing mechanisms.