Evaluation of the energy budget of thermokarst lake in permafrost regions of the Qinghai-Tibet Plateau

Thermokarst lake formation accelerates permafrost degradation due to climate warming,thereby releasing significant amounts of carbon into the atmosphere,complicating hydrological cycles,and causing environmental damage.However,the energy transfer mechanism from the surface to the sediment of thermokarst lakes remains largely unexplored,thereby limiting our understanding of the magnitude and duration of biogeochemical processes and hydrological cycles.Therefore,herein,a typical thermokarst lake situated in the center of the Qinghai-Tibet Plateau(QTP)was selected for observation and energy budget modeling.Our results showed that the net radiation of the thermokarst lake surface was 95.1,156.9,and 32.3 W m^(-2) for the annual,ice-free,and ice-covered periods,respectively,and was approximately 76%of the net radiation consumed by latent heat flux.Alternations in heat storage in the thermokarst lake initially increased from January to April,then decreased from April to December,with a maximum change of 48.1 W m^(-2) in April.The annual average heat fuxes from lake water to sediments were 1.4 W m^(-2);higher heat fluxes occurred during the ice-free season at a range of 4.9-12.0 W m^(-2).The imbalance between heat absorption and release in the millennium scale caused the underlying permafrost of the thermokarst lake to completely thaw.At present,the ground temperature beneath the lake bottom at a depth of 15 m has reached 2.0℃.The temperatures and vapor-pressure conditions of air and lake surfaces control the energy budget of the thermokarst lake.Our findings indicate that changes in the hydrologic regime shifts and biogeochemical processes are more frequent under climate warming and permafrost degradation.

Environmental factors controlling soil warming and wetting during 2000-2020 in permafrost and non-permafrost regions across the Qinghai-Tibet Plateau

The Qinghai-Tibet Plateau(QTP)has experienced rapid environmental changes,including climate warming and wetting,since the 1980s.These environmental changes significantly impact the shallow soil hydrothermal conditions,which have key roles in land-atmosphere feedback and ecosystem functions.However,the spatial variations and responses of soil hydrothermal conditions to environmental changes over the QTP with permafrost(PF)and seasonal frost(SF)remain unclear.In this study,we investigated the spatial variations in soil temperature(ST)and soil moisture(SM)changes over the QTP from 2000 to 2020 using 99 in-situ sites with observations at 4 depths(i.e.10,40,100 and 200 cm).The main environmental controlling factors were further identified using a calibrated statistical model.Results showed that significant(p<0.05)soil warming occurred at multiple soil layers during 2000-2020 with a wide variation(i.e.0.033-0.039℃ per year on average),whereas the warming rates at PF sites were two times greater than those at SF sites.In addition,the soil wetting rate was high over the SF region,whereas the soil wetting rate was low over the PF region.Aside from air temperature,changes in thawing degree days and solar radiation(Srad)contributed most to soil warming in the PF region,whereas changes in rainfall,Srad and evaporation(EVA)have been identified as the key factors in the SF region.As for soil wetting,changes in snowfall,freezing degree days and vegetation have noticeable nonlinear effects over the PF region,whereas changes in EVA,Srad and rainfall highlighted distinct linear and nonlinear effects in the SF region.These findings enhance our understanding of the hydrothermal impacts of future environmental changes over the QTP.

Machine learning-based predictions of current and future susceptibility to retrogressive thaw slumps across the Northern Hemisphere

Retrogressive thaw slumps(RTSs)caused by the thawing of ground ice on permafrost slopes have dramatically increased and become a common permafrost hazard across the Northern Hemisphere during previous decades.However,a gap remains in our comprehensive understanding of the spatial controlling factors,including the climate and terrain,that are conducive to these RTSs at a global scale.Using machine learning methodologies,we mapped the current and future RTSs susceptibility distributions by incorporating a range of environmental factors and RTSs inventories.We identified freezing-degree days and maximum summer rainfall as the primary environmental factors affecting RTSs susceptibility.The final ensemble susceptibility map suggests that regions with high to very high susceptibility could constitute(11.6±0.78)%of the Northern Hemisphere's permafrost region.When juxtaposed with the current(2000-2020)RTSs susceptibility map,the total area with high to very high susceptibility could witness an increase ranging from(31.7±0.65)%(SSP585)to(51.9±0.73)%(SSP126)by the 2041-2060.The insights gleaned from this study not only offer valuable implications for engineering applications across the Northern Hemisphere,but also provide a long-term insight into the potential change of RTSs in permafrost regions in response to climate change.

Application of a concrete thermal pile in cooling the warming permafrost under climate change

Permafrost degradation caused by climate warming is posing a serious threat to the stability of cast-in-place pile foundations in warm permafrost regions.Ambient cold energy can be effectively utilized by two-phase closed thermosyphons(TPCTs)to cool the permafrost.Therefore,we installed TPCTs in a cast-in-place pile foundation to create a unique structure called a thermal pile,which effectively utilizes the TPCTs to regulate ground temperature.And we conducted a case study and numerical simulation to exhibit the cooling performance,and optimize the structure of the thermal pile.The purpose of this study is to promote the application of thermal piles in unstable permafrost regions.Based on the findings,the thermal pile operated for approximately 53%of the entire year and effectively reduced the deep ground temperature at a rate of at least-0.1℃per year.Additionally,it successfully raised the permafrost table that is 0.35 m shallower than the natural ground level.These characteristics prove highly beneficial in mitigating the adverse effects of permafrost degradation and enhancing infrastructure safety.Expanding the length of the condenser section and the diameter of the TPCT in a suitable manner can effectively enhance the cooling capability of the thermal pile and ensure the long-term mechanical stability of the pile foundation even under climate warming.

Thermal and mechanical characteristics of a thermal pile in permafrost regions

Cast-in-place pile foundations are widely used in permafrost regions to support buildings.The stability of cast-in-place pile foundations is highly sensitive to permafrost thermal regime changes.Permafrost degradation caused by climate change is increasing the disaster risk of castin-place pile foundations.However,proactive cooling methods for cast-in-place pile foundations are seldom reported.The cold energy produced by two-phase closed thermosyphons(TPCTs)can efficiently prevent the permafrost thermal regime from being disturbed by engineering activities and climate change.TPCTs were installed in a concrete pile forming a thermal pile.Then,a model experiment was conducted to explore the thermal regime,influence scope,dissipation process of cold energy,and freezing strength of the thermal pile.The results indicated that the thermal pile may significantly cool the foundation soil.Most of cold energy produced by the thermal pile dissipated during the warm period,and the cooling scope of the thermal pile can cover the area within a 40 cm(twice the pile diameter)radius around the pile.Additionally,the TPCTs can significantly improve freezing strength between the thermal pile and frozen soil.The lesson learned from this study can provide a new approach to control the thermal regime of cast-in-place pile foundation in permafrost,which was of valuable to the construction of pile foundations in cold regions.

Evaluation and prediction of engineering construction suitability in the Chinae-Mongoliae-Russia economic corridor

It is proposed to build a high-speed railway through the China‒Mongolia‒Russia economic corridor(CMREC)which runs from Beijing to Moscow via Mongolia.However,the frozen ground in this corridor has great impacts on the infrastructure stability,especially under the background of climate warming and permafrost degradation.Based on the Bayesian Network Model(BNM),this study evaluates the suitability for engineering construction in the CMREC,by using 21 factors in five aspects of terrain,climate,ecology,soil,and frozen-ground thermal stability.The results showed that the corridor of Mongolia's Gobi and Inner Mongolia in China is suitable for engineering construction,and the corridor in Amur,Russia near the northern part of Northeast China is also suitable due to cold and stable permafrost overlaying by a thin active layer.However,the corridor near Petropavlovsk in Kazakhstan and Omsk in Russia is not suitable for engineering construction because of low freezing index and ecological vulnerability.Furthermore,the sensitivity analysis of influence factors indicates that the thermal stability of frozen ground has the greatest impact on the suitability of engineering construction.These conclusions can provide a reference basis for the future engineering planning,construction and risk assessment.