TTOP‐model‐based maps of permafrost distribution in Northeast China for 1961–2020

Abstract

Northeast China has experienced rapid and substantial climate warming over the past 60 years, and permafrost is degrading rapidly. In this study, permafrost distribution and extent in Northeast China were estimated from monitored ground surface temperatures using the temperature at the top of permafrost (TTOP) model and geographically weighted regression method. Using the TTOP model, the computed mean annual ground temperatures (MAGT@TOP) at the top of permafrost of Northeast China increased significantly from 1961–1990 (1.8°C) to 1991–2020 (3.0°C). The areal extents of permafrost defined by a subzero MAGT@TOP (MAGT@TOP ≤ 0°C) in Northeast China in the period 1961–1990 and 1991–2020 were estimated at 461.5 × 103 and 365.8 × 103 km2, respectively, indicating a decline of 95.7 × 103 km2. On average, the simulated MAGT@TOP values were 2.07°C lower than the observed MAGT@TOP values in boreholes. The linear correlation coefficient between the simulated and measured MAGT@TOP values was 0.63. Compared with the simulation results of other previous models, the result of this research is more reliable and accurate. The compiled maps of permafrost distribution can serve as an important reference for the study of permafrost changes in Northeast China.

Influences of Snow Cover on the Thermal Regimes of Xing'an Permafrost in Northeast China in 1960s–2010s

“…The results of this study (2010s) are validated by comparing the 35 GT boreholes in Northeast China collected by Li et al. [33] and the TTOP and permafrost distribution calculated by Li et al. [33] and Obu et al.…”

“…[58], Li et al. [33], and this study. (a,d) Permafrost distribution and TTOP verification results in Northeast China during 2000–2016 as calculated by Obu et al.…”

“…[33] and the TTOP and permafrost distribution calculated by Li et al. [33] and Obu et al. [58] using the TTOP model (Figure 8).…”

“…Li et al. [33] estimated permafrost extent (3.658 × 10 5 km 2 ) in Northeast China during 1991–2020 based on the GST observation data of meteorological stations and underestimated the TTOP compared with the GT borehole data. By considering n f factor, we estimated the permafrost extent in Northeast China at 2.110 × 10 5 km 2 in the 2010s.…”

“…The TTOP model is used to estimate the TTOP by establishing the relationship between ground surface freezing and thawing indices and thermal offsets. Thus, the distribution of permafrost and seasonal frost can be more accurately simulated [33, 57, 58]. The expression for the TTOP model is displayed in Equations ()–() [57, 59]: $$$$ \mathrm{TTOP}=\left\{\begin{array}{c}\frac{1}{P}\left({n}_f\times {I}_f+{r}_k\times {n}_t\times {I}_t\right)\kern0.5em for\ \left({n}_f\times {I}_f+{r}_k\times {n}_t\times {I}_t\le 0\right)\\ {}\frac{1}{P}\left(\frac{1}{r_k}{n}_f\times {I}_f+{n}_t\times {I}_t\right)\kern1.25em for\ \left({n}_f\times {I}_f+{r}_k\times {n}_t\times {I}_t>0\right)\end{array}\right.$$…”