Numerical Simulation Of Permafrost Thawing And Its Impact On Changes Of Lake Reserves In Qinghai-tibet Plateau

Due to global warming,the temperature of the Qinghai-Tibet Plateau(QTP)is also increasing at a rate of 0.3 °C/10 a.As the temperature is rising,a large amount of permafrost distributed in the QTP gradually thawed,and the area of permafrost in China has decreased by 18.6% during the past 30 years.There are a large number of inflow lakes on the QTP,but the lake area of the QTP has generally expanded since 1980,and the total area of lakes on the QTP has increased from 40,000 km3 in 1980 to 50,000 km3 in 2018,an increase of about 25%.The lakes showing an increasing trend are mostly distributed in the inner area of the QTP,that is,areas where permafrost is widely distributed.The continuous increase of lake area in the QTP has attracted wide attention,and there are many studies concentrating on research of its reasons,but most of them are paying more attention on the factors like precipitaion,evaporation,and glacial melting,and the influence of permafrost melting is given less consideration.In order to explore the relationship between the degradation of permafrost and the changes in lake area(reserves)on the QTP under the impact of climate change,this paper chose three large lakes Selinco,Namco,Zhari Namco and a small lake Dangqiongco as study areas.Based on meteorological data as well as remote sensing data,four typical cross-sections of lake basins were established respectively,which coupled variable density groundwater and heat transfer,simulating the process of permafrost melting from 1982 to 2011,evaluating the contribution of permafrost melting to the lake reserves q uantitatively,and predicting the influence of permafrost melting on lake reserves in the next 100 years under the condition of continuous temperature growth.Through simulation and analysis,this article mainly draws the following conclusions : under climate change,the permafrost in four basins in QTP degraded consistently during 1982 to 2011,and during this time the thickness of active layer experienced a process of increasing and then decreasing,and the talik emerged and then kept expending,which can up to 32 m;The groundwater of these four basins all entered the lakes,and the discharge of groundwater accounted for 5.72% ? 16.37% of the average annual lake recharge;With permafrost gradually thawing,the discharge of groundwater kept growing,which has increased by 3.5 times until 2011;According to the scenario prediction in the next 100 years,if the temperature growth rate is unchanged,the permafrost will undergo more severe degradation,and the thickness of talik can reach 68 m,and in the future,only the area from land surface to 5 m above will seasonally freeze in winter,and the discharge of groundwater into the lake will continue to increase.A s a result,the contribution of groundwater into the lake to the water balance of the lake will reach 22.31%.