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Shortened thawing and freezing intervals in the northern hemisphere since 1990 from sites observations and remote sensing.

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Title: Shortened thawing and freezing intervals in the northern hemisphere since 1990 from sites observations and remote sensing.
Authors: Yang, Yanpeng1,2 (AUTHOR), Wang, Xufeng1 (AUTHOR) wangxufeng@lzb.ac.cn, Li, Zongxing3 (AUTHOR), Wang, Tonghong1 (AUTHOR), Che, Tao1 (AUTHOR)
Source: Remote Sensing of Environment. Oct2025, Vol. 328, pN.PAG-N.PAG. 1p.
Subjects: Atmospheric temperature, Remote sensing, Freeze-thaw cycles, Soil temperature, Farms, Land cover
Abstract: The seasonal freeze-thaw (FT) cycles of the permafrost active layer and seasonally frozen ground have significant impacts on ecosystems. Advances in remote sensing have enabled global monitoring of seasonal surface FT cycles. However, previous studies have generally overlooked the impact of remote sensing dataset accuracy on multiple FT parameters and have failed to sufficiently explore the changes in thawing and freezing intervals (TI/FI) in the Northern Hemisphere. This study evaluates the FT-ESDR remote sensing product using site-observed soil temperature data and provides a comprehensive analysis of surface FT characteristics in the Northern Hemisphere, with a focus on freezing and thawing intervals based on FT parameters calculated using a 15-day moving window method. The results indicate that the FT status calculated from site data shows strong agreement with remote sensing data products, with this agreement varying by season, land cover type, air temperature, precipitation. Compared to the FT parameters calculated from site data, FT-ESDR dataset underestimate several FT parameters. Combined analysis of site observation data and remote sensing data products indicates the presence of permafrost degradation, characterized by a longer thawed duration (TD), shorter frozen duration (FD), earlier start of thawing (SOT) and end of thawing (EOT), delayed start of freezing (SOF) and end of freezing (EOF), and reduced FT frequency (FTCF1/FTCF2) for both thawing and freezing seasons. The variations in FT parameters differ based on vegetation and permafrost types. The thawing interval (TI) and freezing interval (FI) show a shortening trend at most sites, indicating an acceleration of the surface thawing and freezing processes. The shortening of TI/FI during thawing/freezing is associated with increased/decreased air temperatures during the corresponding periods. Notably, the variation characteristics of sites in agricultural land differ from those in other land cover types. Overall, our results highlight the underestimation of FT parameters derived from the FT-ESDR dataset and their sensitivity to environmental factors. It also emphasizes the acceleration of surface thawing and freezing processes, which are influenced by air temperature. • The FT-ESDR dataset underestimates surface FT parameters in the Northern Hemisphere. • FT parameter agreement between RS and in-situ data shows spatial differences. • The freezing-thawing interval has accelerated in recent years. • The change in the freezing-thawing interval is linked to air temperature changes. [ABSTRACT FROM AUTHOR]
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Abstract:The seasonal freeze-thaw (FT) cycles of the permafrost active layer and seasonally frozen ground have significant impacts on ecosystems. Advances in remote sensing have enabled global monitoring of seasonal surface FT cycles. However, previous studies have generally overlooked the impact of remote sensing dataset accuracy on multiple FT parameters and have failed to sufficiently explore the changes in thawing and freezing intervals (TI/FI) in the Northern Hemisphere. This study evaluates the FT-ESDR remote sensing product using site-observed soil temperature data and provides a comprehensive analysis of surface FT characteristics in the Northern Hemisphere, with a focus on freezing and thawing intervals based on FT parameters calculated using a 15-day moving window method. The results indicate that the FT status calculated from site data shows strong agreement with remote sensing data products, with this agreement varying by season, land cover type, air temperature, precipitation. Compared to the FT parameters calculated from site data, FT-ESDR dataset underestimate several FT parameters. Combined analysis of site observation data and remote sensing data products indicates the presence of permafrost degradation, characterized by a longer thawed duration (TD), shorter frozen duration (FD), earlier start of thawing (SOT) and end of thawing (EOT), delayed start of freezing (SOF) and end of freezing (EOF), and reduced FT frequency (FTCF1/FTCF2) for both thawing and freezing seasons. The variations in FT parameters differ based on vegetation and permafrost types. The thawing interval (TI) and freezing interval (FI) show a shortening trend at most sites, indicating an acceleration of the surface thawing and freezing processes. The shortening of TI/FI during thawing/freezing is associated with increased/decreased air temperatures during the corresponding periods. Notably, the variation characteristics of sites in agricultural land differ from those in other land cover types. Overall, our results highlight the underestimation of FT parameters derived from the FT-ESDR dataset and their sensitivity to environmental factors. It also emphasizes the acceleration of surface thawing and freezing processes, which are influenced by air temperature. • The FT-ESDR dataset underestimates surface FT parameters in the Northern Hemisphere. • FT parameter agreement between RS and in-situ data shows spatial differences. • The freezing-thawing interval has accelerated in recent years. • The change in the freezing-thawing interval is linked to air temperature changes. [ABSTRACT FROM AUTHOR]
ISSN:00344257
DOI:10.1016/j.rse.2025.114881