# Mapping the Most Susceptible Regions to Fire in Portugal
## 3 Results
### Vegetation Activity Trends and Fire Related Conditions  
Sharp negative GPP\({}_{\rm ANOM}\) are often found in fire scars and prevail in the following years, as in the cases of 2003, 2005, and 2017 (see Figure S2). Observing Figure 2a, \(\Sigma\)GPP\({}_{\rm ANOM}\) presents a clear signature (negative values) over the burned areas in northern and southern parts of Portugal, being particularly pronounced in central Portugal.  
The maps of \(\Sigma\)GPP\({}_{\rm ANOM}\), on one hand, and the maps of GPP\({}_{\rm TREND}\) and NPP\({}_{\rm TREND}\) on the other, (Figure 2b,c, respectively) reveal contrasting patterns. A general positive GPP\({}_{\rm TREND}\) and NPP\({}_{\rm TREND}\) is found along the territory, with exceptions for some more recent burned areas, indicating a general increasing trend in vegetation productivity over the last two decades. The trends agree with the overall observed annual time-series, while the \(\Sigma\)GPP\({}_{\rm ANOM}\) are strongly influenced by monthly disturbances.  
Figure 1: (a) Elevation of Portugal, in metres high; (b) fire frequency at pixel-level between 2001 and 2021; (c) time without burn (TwB) in the period 2001–2021.  
The areas nearer to the shore, as well as the southwest region of the country, have the highest positive trends, with \(\mathrm{GPP_{TREND}}\) of about 0.01 kg C/m\({}^{2}\)/month and \(\mathrm{NPP_{TREND}}\) above 0.20 kg C/m\({}^{2}\)/year.  
The persistence of 'Very High' and 'Extreme' fire danger classes is noticeable in Figure 2d, where the south, as well as the centre of the country, reveal probabilities of finding these classes above 20-25%, whereas other regions have probabilities lower than 20% (as estimated for the 1980-2021 period). Besides FWI, FRE, as shown in Figure 2e,  
Figure 2: (**a**) Sum of monthly \(\mathrm{GPP_{ANOM}}\) over the period 2001–2021; (**b**) linear trend of GPP between 2001 and 2021; (**c**) same as (**b**) but for NPP; (**d**) probability of occurrence of FWI classes ‘Very High’ and ‘Extreme’ between 1979 and 2021; (**e**) median Fire Released Energy, expressed in gigajoules, between 2004 and 2020; (**f**) Fire Risk Map between 2017 and 2021. These nine variables are the ones which are used to be used in the PCA.  
reveals values of about 250-500 GJ over most of the points where the fire events occurred. Nonetheless, much higher values can be found, especially in the centre of the country. Intense fire occurred in these regions, promoting FRE values above 1000 GJ and, in some spots, FRE reached values even higher than 2000 GJ. In the southernmost part of Portugal, high values are also found, especially in the southwestern (about 1000-1500 GJ) and southeastern (about 1750-2000 GJ) regions. FRM, which is illustrated in Figure 2f, is higher in the centre and the south of the country, similarly to FRE. In these regions, the percentages of fire risk vary from 60 to 70% in the south and 40 to 50% in the centre of the country.  
The occurrence and intensity of wildfires are closely linked to favourable weather conditions. During the last four decades, these conditions have been enhanced, as shown by FWI classes in Figure 3. A general increase in the probability of occurrence of more-severe classes of FWI has been observed throughout the territory, with a northward expansion crossing the Montejunto-Estrela mountain range (see Figure 1a). Two danger classes stand out: the 'High' and the 'Very High'. The probability of occurrence of class 'High' increased about 5% in the last four decades while the 'Very High' probability increased about 5-10% in the same period. Furthermore, the probability for the 'Extreme' class shifted from residual cases (0%) in 1980-1990 to about 3-5% in 2010-2020.