# Mapping the Most Susceptible Regions to Fire in Portugal
## 2 Materials and Methods
### Data
#### 2.1.2 Burned Area and Fire Related Variables  
The detection of the burned areas relied on the MODIS Burned Area product, MCD64 Collection 6 [39], with a spatial resolution of 500 m; here, we considered data for the months between June and October over the 2001-2021 period. This product showed several improvements regarding the previous version, especially in small fires detection, but also in the reduction in burn-date uncertainty. Data were generated relying on daily surface reflectance dynamics so the algorithm could detect the more likely date of fire, as well as the spatial extent of the events.  
Fire weather index (FWI) corresponds to an output from the Canadian Forest Fire Danger Rating System [40]. The index has shown to be an accurate measure of fire danger across different land covers on a global scale, especially over flammability-limited environments [41; 42]. In fact, [PERSON] et al. [43] highlighted that FWI is a particularly suitable index to monitor fire danger over the Mediterranean region. Therefore, FWI is an appropriate index for our study with the aim of monitoring fire danger over the last years.  
FWI is organised into six different components: three fuel moisture codes--Fine Fuel Moisture Code, Duff Moisture Code, and Drought Code--which together integrate information regarding the effect of fuel state and availability on fire danger; the weather-driven fuel moisture information is encompassed in two indices that measure the rate of fire spread (Initial Spread Index) and the available fuel for combustion (BuiltUp Index) [40]; the sixth component, named FWI, combines all the previous information, including daily meteorological variables, namely temperature and relative humidity at 2 m, wind speed at 10 m, and 24 h accumulated precipitation. FWI was extracted from the most recent reanalysis of the European Centre for Medium-Range Weather, ERA5 [44], with daily availability and a spatial resolution of 0.25\({}^{\circ}\), between 1979 and 2021.  
Fire Released Energy (FRE) relies on hourly Fire Radiative Power (FRP) derived from Meteosat Second Generation (MSG) observations [45] provided by Satellite Applications Facility on Land Surface Analysis (LSA-SAF). Daily values of fire released energy are then determined for the period comprising 2004 (i.e., the start of MSG observations) to 2020, through the integration of FRP hourly values over 24 h periods on a pixel-by-pixel basis [46]. To obtain the map of characteristic released energy over the 2004-2020 period, the median value of FRE was determined at pixel-level.  
The fire risk map (FRM), also generated by the LSA-SAF, combines information from Numerical Weather Prediction models, vegetation classes, and historical values of MSG FRP data to accurately characterize the fire danger [47]. Here, we used all available data from the most recent version of LSA-SAF FRM product, i.e., for the period comprising 2017 to 2021. FRM values are expressed as the percentage of the occurrence of the most extreme fire danger classes (Classes 4 and 5) in the considered period.  
All the variables used in this study, with the correspondent spatial and temporal coverage, are summarized in Table 1.