Mapping of burned area and assessment of burn severity of the 2017 wild fires in Kresna gorge

At the end of the summer of 2017, the weather in Bulgaria was very dry and hot and this contributed for the occurrence of a series of wild fires. The largest and most prolonged was the wild fire that raged in Kresna gorge. The fire broke out on August 24 and lasted for nearly a week. The aim of the paper is to make an assessment of the damage caused by the August fire and by a smaller wild fire in the same region, which broke out on July 13, 2017. The assessment is based on images from the satellites Sentinel-2A and -2B. For the identification and mapping of burned areas the spectral indices NBR (Normalized Burn Ratio) and dNBR (difference NBR) were used. Map of burn severity within the fire perimeter was compiled by reclassifying the dNBR values into three classes. The total burned area was 2199.1 ha; of this, the August fire covered 96%. The greatest part of the fire scar, over 50% of the area, is characterized with medium burn severity (dNBR between 0.27 and 0.66). Both, the lowest (dNBR between 0.1 and 0.27) and highest (dNBR>0.66) burn severity levels covered about ¼ of the total burned area. A map of the major land cover types in the study area was prepared in order to assess the most severely affected land cover types. The map is derived from supervised SVM (Support Vector Machine) classification of a Sentinel-2B image acquired before the fires. It was found that the coniferous forest class is dominated by the highest burn severity level (43.7% of the area). In the broadleaf forest class the areas with the lowest level of burn severity prevail (53.5%). The main reason is that coniferous forests in the study area represent artificial plantations created at altitude lower than the usual altitude of coniferous species in the region. Therefore they are much more susceptible to fire than broadleaf species which are native to the oak belt