The Contribution Of Permafrost Degradation To Lake Expansion Based On SBAS-InSAR In Hohxil Lake Basin Of Qinghai Tibet Plateau

The Qinghai-Tibet Plateau(QTP)is known as the"Third Pole"of the Earth,of which unique geographical environment is very sensitive to the global climate.Due to climate warming,the permafrost of the QTP has undergone serious degradation,and the plateau lakes have shown an obvious expansion trend in recent decades.The QTP is rich in water resources,with the largest number of lakes,glaciers and underground ice volume in China.Therefore,timely monitoring the change of permafrost is of great significance to the ecological security,social stability and economic development of the QTP region.Taking the Hohxil Lake(HL)basin in the north of QTP as an example,this study extracted the permafrost deformation information from 2015 to 2020 based on the small baseline subset interferometric synthetic aperture radar(SBAS-InSAR),analyzed the deformation characteristics of permafrost in the basin,calculated the volume change of permafrost underground ice,and evaluated the contribution of ground ice meltwater to the lake expansion,which provided a new perspective for permafrost hydrology.The main contributions and conclusions of this study were as follows:(1)Not only had obvious long-term thawing settlements been detected,but also permafrost uplift occurred meanwhile.The subsidence signals were mainly distributed in the flat terrain of the basin,such as the outwash plain of the Malan Glacier and coastal areas of the HL,while the uplift signals were mostly distributed on the gentle slopes of mountain.(2)In terms of simulating permafrost deformation,the periodic model(PM)could more reliably reflect the deformation characteristics of permafrost than the traditional linear model(LM),but the results of permafrost deformation rate inversed by the two models were not much different.The average rates of the LM and PM of subsidence were-3.59 cm/a and-3.60 cm/a,respectively;and the average rates of LM and PM of uplift were both 2.11 cm/a.(3)In the course of SBAS-InSAR technique processing,the sequential connection was sensitive to the experiment results of permafrost deformation.In terms of subsidence signals alone,the volume of underground ice meltwater retrieved by LM and PM under the same connection parameter were relatively close.However,in terms of uplift points,there were obvious differences between the results of different sequential connections under the same model and the same sequential connection under different models.(4)There were obvious funnel-shaped settlement areas in the permafrost around the HL.The closer to the center of the funnel,the greater the subsidence rate of the permafrost;and the settlement rate in the center area reached about-12 cm/a.This may be related to the rapid expansion of the lake that changed the hydraulic conductivity and thermal conductivity of the soil,indicating a close relationship between the expansion of the lake and the melting of underground ice.(5)The change of HL water volume from 2015 to 2020 was aout 1.55×10~9 m~3,and the average underground ice meltwater volume of permafrost was approximately 1.5663×10~8 m~3,accounting for 10.1%contribution to the lake expansion.Glacier meltwater contribution rate was approximately 10.0%based on the existing study and according to the principle of mass budget for closed lakes,about 79.9%contribution rate of precipitation was estimated,indicating that precipitation was still the leading factor in the lake expansion.