Multidecadal satellite-derived Portuguese Burn Severity Atlas (1984-2022)

Abstract

Long-Term burn severity assessment can support better pre-and post-fire management plans. In this study, the Portuguese Burn Severity Atlas was created, containing historical fires in Portugal from 1984 to 2022. As prerequisites, fire data were gathered and delimited for all years. Due to the availability of satellite images, for different years, different imageries from Landsat sensors (30 m) were applied. Exploratory analysis showed that burn severity estimates are significantly affected by the time lag between the satellite imagery acquisition and the fire date. We explicitly incorporated the effect of time lag into the degradation of burn severity estimates in the selection of the most suitable pre-and post-fire satellite images for each fire. Using Google Earth Engine, burn severity estimates were calculated for fires that were equal to or larger than 100 ha and that occurred from 1984 to 2022 with known dates (valid fires). Different indices were calculated, such as the differenced normalized burn ratio (dNBR), the relative dNBR (RdNBR), the relativized burn ratio (RBR), and a burn severity index that combines the dNBR with the enhanced vegetation index (dNBR-EVI). Overall, in Portugal, 4.85×106 ha burned over the 38-year period (1984-2022), with the burned area covering 3.29×106 ha being caused by valid fires (68 %). Among these, a total area of 3.18×106 ha had burn severity estimates via the applied indices (97 % of valid and 66 % of all fires). Results show that Portugal has experienced, on average, "high"burn severity throughout this period, with large percentages of dNBR pixels between 0.419 and 0.66 (32 %) and >0.66 (21 %). Estimates from different burn severity indices provided a more complete representation of the burn severity impacts. This atlas can be accessed at 10.5281/zenodo.12773611 (Jahanianfard et al., 2025) and can be used by researchers to have a better understanding of historical fires and their corresponding impacts on vegetation cover, air, soil, and water quality, as well as to identify the most influential environmental and climatic drivers of burn severity.