The Signature of Climate in Annual Burned Area in Portugal

Portugal is by far the country most affected by wildfires in Mediterranean Europe. The increase in frequency and severity of extreme years in the last two decades calls for a better understanding of the role played by climate variability and climate change. Using data covering a period of 44 years (1980-2023), it is shown that the distribution of annual burned area in Portugal follows a Rayleigh distribution whose logarithm of the scale parameter depends linearly on Cumulative Daily Severity Rate (CDSR). Defined for each year as the sum of the mean Daily Severity Rate over Portugal from 1 January to 31 December, CDSR is a measure of the dryness of dead fuels as induced by atmospheric conditions. Changes along the years of the modeled average explain 56% of the interannual variability of the annual burned area. When comparing the model for 30-year subperiods 1980-2009 and 1994-2023, large decreases are observed in return periods of annual burned area amounts, from 35% for amounts greater than 120 thousand hectares up to 49% for amounts greater than 200 thousand hectares. The proposed model is a useful tool for fire management under present and future climate conditions.