Fig. 5: Structural equation model (SEM) analysis of environmental drivers affecting spatiotemporal changes in permafrost.
a Path diagram illustrating the hypothesized causal relationships. Single-headed arrows indicate the direction of causation. Black solid arrows indicate significant positive relationships, black dashed arrows indicate significant negative relationships, and gray arrows represent insignificant relationships. Rectangles represent the principal components for groups of climate variables: air temperature, precipitation, solar radiation, wind speed, surface pressure, and specific humidity; freezing level height (FLH); soil water content; and underlying factors including soil temperature and vegetation. Permafrost characteristics include active layer thickness (ALT), temperature at the top of permafrost (TTOP), and permafrost temperatures at 10 m and 15 m depths (PT10m, PT15m). Permafrost changes refer to changes in these attributes. Model fit indices reported are coefficient of determination (R²), chi-square divided by degrees of freedom (χ²/df), goodness of fit index (GFI), adjusted goodness of fit index (AGFI), and root mean square error of approximation (RMSEA). b bar graphs show the standardized direct, indirect, and total effects of environmental variables on permafrost characteristics (top panel) and permafrost changes (bottom panel). Asterisks indicate statistical significance (***p < 0.001).
