| 28 Oct 2025
Linking Permafrost Deformation to Active Layer Freeze-thaw Dynamics in the Qinghai-Tibet Engineering Corridor
Abstract. The Qinghai-Tibet Engineering Corridor (QTEC), traversing hundreds of kilometers of sensitive permafrost, hosts critical lifelines increasingly threatened by climate-induced ground deformation and thermokarst disasters. However, we still lack knowledge about the spatiotemporal characteristics of permafrost states and associated ground deformation at a finer scale. Here we derive ~120-m-resolution surface displacements during 2014–2022 from Sentinel-1 interferometric synthetic aperture radar (InSAR) data processing. We disentangle secular displacement rates from seasonal variations, quantified seasonal amplitudes and timings, and determine displacement directions through complementary ascending and descending observations. Results reveal extensive subsidence throughout the QTEC, exceeding 20 mm/year in areas between Golmud and Nagqu. Seasonal deformation, driven primarily by frost-heave, thaw-settlement cycle of permafrost, can surpass 40–80 mm, with valley floors peaking in spring and hillslopes peaking in autumn due to different hydro-thermal and mechanical responses. Seasonal amplitude of vertical displacements effectively constrains ALT, indicating ALT ≥1 m where seasonal amplitude exceeds 55 mm. With the constraint from in-situ ALT measurements and the assumption of a complete ice melt in the fall, a freeze-thaw density-change model pictures a regional map of ALT at high resolution, where the permafrost to the west of QTEC exhibits a greater ALT compared to the eastern section. Alarming numbers of thermokarst phenomena (18 thaw slumps, 2,812 thaw lakes) within 2 km of critical infrastructure underscore escalating hazards. Our findings emphasize the urgent need for integrated monitoring and adaptive strategies to mitigate intensifying risks from permafrost degradation across the QTEC.
Comments to the Authors
The authors describe a study that derives surface displacement from InSAR data in an effort to determine changes in active layer thickness in the QTEC. The manuscript addresses an important topic because understanding of changes in permafrost conditions and the implications for ground stability is important for informed engineering design and adaptation to a changing climate. However, I have some concerns with the interpretation of results and their validation. My expertise is related more to permafrost related processes rather than use of InSAR data and my comments are therefore related to interpretation of the surface displacement results.
The amount of surface displacement including ongoing subsidence of the ground as permafrost thaws depends on the surficial material characteristics, especially the ground ice content. Excess ice (ice that when melted exceeds the water holding capacity of the material) content is especially important for thermokarst processes which have implications for infrastructure. A large change in ALT therefore does not necessarily result in large changes in surface elevation because thaw of ice-poor material will yield less displacement than an equivalent amount of thaw in ice-rich material. No information on surficial geology or the potential for ice-rich material has been presented in the manuscript, and this is important for the interpretation of the displacement results. It is also unclear whether the occurrence of excess ice (and the ice segregation process) has been considered or only the formation and melt of pore ice. See additional comments below.
Validation of the modelled ALT values using field data is also unclear. A lot of data has been collected in the QTEC that facilitates estimates of ALT and also descriptions of subsurface material characteristics, including ice content and thaw sensitivity. The lack of clarity regarding how this field-based information was utilized makes it difficult to evaluate the validity of the analysis used to derive the ALT results.
The manuscript also requires editing to improve, language, terminology and clarity.
Additional comments on the manuscript are provided below.
Additional Comments
L31-104 Introduction– This needs much work. Better organization and reduction of text to focus on only the information that is relevant would be beneficial. Some of the statements are unclear or incorrect. Editing is required to improve language.
L31-35 –Note it is thaw of ice-rich material that can result in ground deformation so it is not necessarily caused directly by climate change. Use “thermokarst processes” rather than “thermokarst disasters”. A disaster depends on the consequences of the process and whether they are important with respect to infrastructure, human life for example. Note, the active layer is not part of permafrost. The last sentence in the paragraph about GCOS is not really necessary. It is sufficient to refer to active layer thickness as an indicator of permafrost change.
L44-55 – When describing rates of change, the period over which the change has occurred should be given. Here and elsewhere in the paper – refer to permafrost thaw rather than melt. Several statements are unclear or use poor terminology. Repetition needs to be reduced.
L57 – Delete “dynamic” redundant (“changes” is sufficient)
L57-60 – I assume you are referring to topographic surveys that utilize GNSS, i.e. measuring surface elevation. Surface displacement isn’t directly measured but derived from elevation measurements made over time.
L63-65 – It is incorrect to say InSAR-derived displacement patterns directly reflect permafrost dynamics. They reflect changes in surface elevation. Surface displacement can be caused by various processes including groundwater withdrawal, sediment compaction, crustal movements etc. Slope movements aren’t necessarily triggered by permafrost change. The attribution of changes requires knowledge of the local conditions including materials and their thermal state, and geologic/geomorphic processes etc. – result of analyses of different types of data.
L73 – “linear subsidence” is unclear – is this vertical subsidence?
L76-79 – Is this rate for seasonal movement or cumulative over several years?
L98-104 – Is information on surficial geology and ground ice content used. Knowing ALT on its own is sufficient when determining displacement patterns. Is excess ice considered?
L120 – “compiled” is probably more correct than “collected”
L176 – What is meant by long-term – what is the period considered.
L213 – Replace “can hardly” with “can not”
L222 – Is this based on cumulative subsidence over several years or just seasonal movement?
L225 – Avoid words like “drastic”
L226-227 – Permafrost isn’t required to have seasonal heave and subsidence as this can occur where only seasonally frozen ground is present. The change may have more to do with a change in surficial geology and frost susceptibility.
L253 – Are displacements more pronounced here due to the surficial materials?
L262-263 – Occurs at/prior to the onset of thaw?
L312-313 – It is unclear whether there is consideration of segregation ice (ice lens formation) which forms as water migrates to the freezing front or just the 9% expansion of pore ice. The segregation process is responsible for excess ice formation which is important for thermokarst processes.
L315-321 – It takes time for changes in surface temperature to propagate to greater depths. Thaw may still be occurring at depth when onset of freezing occurs at the surface.
L333-335 – ALT can be derived from ground temperature measurements, frost probing and thaw tubes. I’m not sure that most would call extraction of stratigraphic profiles the most fundamental method of determining ALT.
L350 – Is excess ice considered?
L361-362 – ALT is not directly measured using GPR surveys but interpreted from the data – requires additional site knowledge etc.
L380-388 – How do these derived values of ALT compare to measured values?
L413-415 – Refer to thermokarst processes rather than disasters.
L412 – Section 4.3 – The rest of the paper focussed on vertical displacements derived from InSAR. It isn’t clear whether displacements derived from InSAR are used to generate the results presented here regarding thaw slumps etc. or some other technique given other satellite products are mentioned.
L493-496 – Note that these studies do not consider infrastructure design in their analysis. This is important because infrastructure design will influence the impact of permafrost thaw on the infrastructure. These studies are often done at scales that are insufficient for more regional to local scale assessments which are required when considering infrastructure impacts.