Drought and wildfires in Portugal at the county scale

Weather and climate extreme events contribute to the increase of wildfire risk. A recent study carried out in Mainland Portugal for the period 1981 – 2017, using Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI) to assess drought conditions, revealed that drought affects 70% of the months and a very strong relationship between the occurrence of drought and the spatio-temporal distribution of extreme wildfires (> 5,000 ha). These results raised additional scientific questions that need to be answered, such as: Is the relationship between droughts and fires equally strong for wildfires of smaller size? The study was carried out at the country level, but what are the regions where the relationship is more and less strong? Therefore the objective of this study is to assess the influence of drought on fire incidence, considering all wildfires or classes of wildfire sizes and in each of the 278 counties of Continental Portugal characterized by different features (landscape, weather/climate, drought and fire incidence). This study benefits from the existence of long and reliable meteorological and wildfire datasets. The methodology comprises cluster analysis, contingency tables, accuracy metrics, statistical measures of association to test the independence and help find interactions between these two natural hazards. Main results include: (i) the characterization of spatio-temporal distribution of drought number, duration, severity, intensity, extension; (ii) wildfire space-time distribution within drought periods and affected area; and, (iii) the assessment of the relationship between droughts and wildfires at county scale. The authors believe that the findings of this study are very useful for the definition of adaptation and mitigation strategies for the impacts of droughts in wildfire occurrence and to assess the climatic wildfire hazard/risk.

Acknowledgements

This work was supported and conducted in the framework of the FEMME project (PCIF/MPG/0019/2017) funded by FCT - Portuguese Foundation for Science and Technology. The study was also supported by: i) National Funds by FCT - Portuguese Foundation for Science and Technology, under the project UIDB/04033/2020; and, ii) National Funds by FCT - Portuguese Foundation for Science and Technology, under the project UID/AMB/50017/2019. Data were provided by the European Forest Fire Information System – EFFIS (http://effis.jrc.ec.europa.eu) of the European Commission Joint Research Centre.