Spatio-temporal analysis of permafrost freeze–thaw cycles patterns in the Qilian Mountains using InSAR-derived deformation and MODIS LST data

Abstract

This study presents a comprehensive spatiotemporal analysis of permafrost freeze–thaw cycles in the northeastern Qilian Mountains, a climatically sensitive region on the northeastern Tibetan Plateau. Ground deformation time series were derived from Sentinel-1 InSAR data using the LiCSBAS open-source processing framework, while land surface temperature time series were from MODIS Terra and Aqua sensors and reconstructed using the Harmonic Analysis of Time Series (HANTS) algorithm. By integrating these datasets, this study investigated spatial and temporal patterns of annual vertical velocity and seasonal deformation amplitude. Results reveal significant spatial heterogeneity. Persistent subsidence dominated valley basins and gentle terrains, while uplift occurred mainly in high-elevation, steep-slope zones. High seasonal deformation amplitudes, indicating intense freeze-thaw activity, concentrated in moisture-retentive alpine meadows and low-slope basins. Crucially, distinct phase lags existed between surface temperature zero-crossings and annual ground deformation extrema. In gentle basins, peak uplift preceded consistent above-freezing LST by 1-2 months, while maximum subsidence aligned with the transition to subzero temperatures. High-altitude steep slopes exhibited significantly delayed responses: peak uplift lagged about 2 months behind the LST upward zero-crossing, and maximum subsidence occurred 4 months after the downward zero-crossing. These findings demonstrate that multi-sensor remote sensing provides a integrated perspective for monitoring and analyzing permafrost freeze–thaw cycles.