Distribution And Regional Changes Of Thermokarst Lakes On The Qinghai-Tibet Plateau

The Qinghai-Tibetan Plateau(QTP),the largest high altitude and low latitude permafrost zone in the world,has been experienced rapid permafrost degradation in the past decades,and one of the most remarkable characteristics is the formation of thermokarst lakes.The thermokarst lakes have created many concerns because they can regulate carbon cycle,water and energy fluxes.However,thermokarst lakes distribution in this area largely remains unknown,and this knowledge gap hinder our understanding of response of permafrost and its carbon feedback to climate change.In permafrost regions in the future development of thermokarst lakes,plays an important role on the climate warming,the change of thermokarst lakes current distribution and the future development trend of research has the necessity and urgency,at the same time,the establishment of the database to thermokarst lakes distribution and change,can better explain and predict the thermal karst landforms in permafrost regions of the effects of global climate change and carbon cycle.Combined with field investigation and monitoring,the temporal and spatial distribution characteristics of thermokarst lakes on the Tibetan Plateau in 2018 were studied using Sentinel-2A and Landsat data.At the same time,the environmental factors affecting the distribution of the thermokarst lakes were discussed,and the change trend of the thermokarst lakes in the future was simulated by using machine learning method.The results provide a scientific basis for the assessment of environmental change on the Qinghai-Tibet Plateau,the development process of thermal karst,the feedback of climate change in permafrost regions and the impact on carbon cycle.The main research results are as follows:1.For the first time,we provided the spatial distribution of thermokarst lakes at the spatial resolution of 10 m.The ratio of average absolute error(MAE)and root-mean-square error(RMSE)was close to 1:1.The results show that the thermokarst lakes area on the QTP is 1730.43 km2,accounting for 4%of the total water area of lakes and ponds,and the thermokarst lake density is 12/100 km2.Most of thermokarst lakes were distributed in the alpine meadow,steppe and barren land,and the densities of thermokarst lakes in alpine desert(16/100 km2)and barren land(17/100 km2)were larger than alpine meadow(13/100 km2),alpine steppe(11/100 km2)and wet meadow(11/100 km2).2.In addition,through the study of the distribution of thermokarst lakes along the Qinghai-Tibet Highway in recent 29 years(1991-2020),it can be seen that the number and area of thermokarst lakes along the Qinghai-Tibet Highway show a trend of decreasing-increasing-rapidly increasing-decreasing.The area of thermokarst lakes increased from 107.14 km2in 1991 to 184.92 km2in 2020.The density of thermokarst lakes along the Qinghai-Tibet Highway is generally high.In 2018,the density of thermokarst lakes along the Qinghai-Tibet Highway was 14.4/100km2.The thermokarst lakes along qinghai-tibet highway in alpine meadow vegetation type under most,about48%of the total area of the thermokarst lakes along qinghai-tibet highway,alpine grassland,followed by thermokarst lakes much distribution along qinghai-tibet highway where the precipitation is 400-600 mm,2020 thermokarst lakes most distribution in precipitation<400 mm area,about 80.79%of the thermokarst lakes located in<400 mm area.3.In different situation of thermokarst lakes CMIP5 simulation results and the actual thermokarst lakes along qinghai-tibet highway,1991-2020 data comparison test,the error between 2.27%and 27.52%.In 4.5,8.5 and RCP2.6 scenario,thermokarst lakes along Qinghai-Tibet highway area will increase 18.89-21.89 km~2.Overall,three scenarios and down,from 2020 to 2100,thermokarst lakes along qinghai-tibet highway are all showed a trend of increase thermokarst lakes at the same time,the QTP lakes area of a general increasing trend,in RCP2.6,4.5 and 8.5 scenario,the QTP thermokarst lakes area increased,peaked around 2050.In RCP4.5 situation,the QTP showed a trend of increasing the thermokarst lakes area,in 2040 and 2060 before and after a brief decline,to around 2080 thermokarst lakes area has increased rapidly,to a maximum2100.Under the RCP8.5 scenario,the area of thermokarst lake in the QTP will increase rapidly and reach the maximum value in 2100.This study provides a high-resolution data set for the thermokarst lakes and their controlling factors on the QTP,provides the distribution trend of thermokarst lakes along the Qinghai-Tibet Highway in the past 30 years,and predicts the area change of thermokarst lakes under the future scenario.It provides important data for the study of the impact of climate change on the ecology and environment of permafrost regions,and provides important materials for the construction of ecological safety barriers in China.