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Figure 1. Location of the investigated regions and observation sites. Green dots and red triangles stand for the mean annual ground temperature (MAGT) and active layer thickness (ALT) monitoring sites, respectively. The black polygons depict the five typical regions.
Figure 2. Observed vs . simulated mean annual ground temperature (MAGT) for 84 borehole sites based on four statistical techniques (GLM = generalized linear model, GAM = generalized additive model, GBM = generalized boosting method, RF = random forest.) and an ensemble method (the average of the four methods). The red dashed lines are the ±1 ℃ intervals around the 1:1 line (in black solid line).
Figure 3. Observed vs . modeled active layer thickness (ALT) based on four statistical techniques (GLM = generalized linear model, GAM = generalized additive model, GBM = generalized boosting method, RF = random forest.) and an ensemble method (the average of the four methods). The red dashed lines are the ±1 m interval around the 1:1 line (in black solid line).
Figure 4. Spatial distribution of permafrost on the QTP based on the MAGT.
Figure 5. Distribution of the ALT on the permafrost regions of the QTP.
Figure 6. Forecast mean annual ground temperature (MAGT) and active layer thickness (ALT) across the study domains under different RCPs (RCP2.6, RCP4.5 and RCP8.5) for the 2070s (average of 2061−2080).
Figure 7. The uncertainty related to the spatial forecasts of mean annual ground temperature (MAGT) and active layer thickness (ALT) in RCP 2.6(a), RCP 4.5 (b), RCP 8.5 (c) scenarios. The uncertainty is quantified using a repeated (n = 1,000) bootstrap sampling procedure inside the study domain. The boxplots depict the mean, median, 1st and 3rd quartiles and range of variation over 1000 predictions for modeling techniques.
Figure 8. Projections of the changes in permafrost area on the QTP under RCP2.6, RCP4.5, RCP6.0 and RCP8.5 via 7(a) surface frost index (SFI) and 7(b) Kudryavtsev method (KUD). The graph is derived from Changet al. (2018). Shaded areas show the standard deviations across the CMIP5 models, the black lines show the equivalent present-day area, and the grey dotted line represent the degraded area in 2070 under different RCPs.
Figure 9. Spatial differences between our results (2000–2015) and those of Zou et al (2003–2012; TTOP model). P and SFG represent permafrost and seasonally frozen ground, respectively; Result is the permafrost distribution of this study. The permafrost distribution is obtained from Zou et al. (2017).
Figure 10. Spatial distribution of the permafrost regions prone to degradation.
Table 1. Model Error statistics of the ALT and MAGT in different typical regions