Fig. 3: Climatology and changes in preconditioned drought and fire weather.
From: Global increase in wildfire potential from compound fire weather and drought
a Number of preconditioned drought \({P}_{a} \,<\, {\mu }_{{P}_{a}}-{\sigma }_{{P}_{a}}\) and fire weather \({{{{\rm{FWD}}}}}_{f} \,>\, {\mu }_{{{{{\rm{FWD}}}}}_{f}}+{\sigma }_{{{{{\rm{FWD}}}}}_{f}}\) years 1970–2020. b Change in number of preconditioned drought and fire weather years from 1971-1995 to 1996-2020. c–h Annual number of fire weather days, \({{{{\rm{FWD}}}}}_{f}^{r}\) (orange), and antecedent precipitation, \({P}_{a}^{r}\) (blue), for six IPCC regions. The data are scaled to have unit variance and adjusted such that the threshold for drought (\({\mu }_{{P}_{a}^{r}}-{\sigma }_{{P}_{a}^{r}}\)) and fire weather (\({\mu }_{{{{{\rm{FWD}}}}}_{f}^{r}}+{\sigma }_{{{{{\rm{FWD}}}}}_{f}^{r}}\)) years are the same. The y-axis for precipitation is inverted such that both drought and fire weather years lie above the threshold (the black horizontal line labelled μ ± σ). Preconditioned drought and fire weather years are indicated by vertical grey lines. i-k Proportion of area in drought, fire weather, and preconditioned years, respectively. Colours indicate data for the Northern Hemisphere, the Southern Hemisphere, the tropics, and global.
