Mapping burn severity and uncovering spread patterns of the 2021 Varibopi wildfire

Abstract

This work unveils how the wildfire of August 3rd, 2021 that initiated at the northeastern part of Attica (Varibopi), spread and burned during the four days of its active propagation. This fire is a characteristic large-scale event that affected the wildland-urban interface of Athens, revealing weaknesses of both pillars of fire management: prevention and suppression. Initially, we provide a short description of how and under which conditions (vegetation and weather) the fire initiated and propagated after debriefing reports, news articles and satellite data. Then, we applied the difference Normalized Burn Ratio on a pair of Sentinel 2A satellite images (one right before and another taken one year later) to map the extended burn severity and delineate the fire perimeter. Finally, using the Minimum Travel Time Algorithm, we simulated major spread vectors and rate of spread to answer how the fire would have been evolved in the absence of active fire suppression. We found that from the 8,445-ha included in the final delineated perimeter, 1,000 ha were unburned, 4,715 ha experienced low or moderate-low burn severity, and 2,730 moderate-high or high burn severity. Without suppression, the fire could have escaped from three directions to the west with high spread rate, potentially affecting the Parnitha National Park. The most imminent post-fire issue is not whether the conifer vegetation will recover, but if during the next decade vegetation management measures are not applied in selected locations, then a new ignition can spread faster and burn a more extended area compared to the 2021 fire.