Extended Data Fig. 6: Spatial patterns of fire behavior and the linear relationships between fire behavior variables and fire size across northern forests (40°N–70°N) at a 2° resolution.

The first column displays the mean values of fire duration (a), fire spread rate (d) and fire radiative power (FRP, g) by averaging all fire patches within each 2° grid cell. Panels (b, e) and (c, f) show the regression slope (β) and the coefficient of determination (R²), respectively, which are derived by fitting linear regression model (log₁₀(fire size) = α + β × x) within 2° grid cells, where x stands for fire duration (b, c) and fire spread rate (e, f). Panels (h) and (i) show the β and R² derived by fitting a linear regression model (FRP = α + β × log₁₀(fire size)) within 2° grid cells. Only grid cells with >10 fire events were included in the regression analysis. Both solid and empty dots indicate pixels with locally significant regressions (p < 0.05, the two-tailed t-test), but solid dots indicate those having passed a more rigorous field significance test corrected for the false discovery rate (α_FDR = 0.10, see Methods). The light grey background in all maps indicates northern forests with a > 10% ground coverage. Figure developed using the Python open-source tools.