Spatial Distribution Patterns of Wildfire Ignitions in Portugal

Burnt area in Portugal increased in the last decades, contrarily to other southern European countries. On the other hand, the number of wildfire ignitions is increasing in Portugal, Spain and Greece, but in Portugal its occurrence density is much higher. Since 2000 Portugal registered an average of about 28,500 fire ignitions every year, and this situation causes an important dispersion of detection and fire fighting resources, contributing to reduce their effectiveness. In order to evaluate the distribution of wildfire ignitions, we analyzed 127,492 fires detected in Portugal during the period 2001-2005 in relation to variables such as population density, proximity to urban areas and road network, land cover types, altitude, causes and final burnt area. Results showed that most part of fire ignitions are concentrated in the north and centre littoral areas, in the most populated municipalities, and were intentionally caused. Although municipalities with more than 100 persons per km2 only represents 21 % of the territory, they concentrated more than 70 % of fire ignitions occurring in Portugal, but only about 14 % of total burnt area. We verified that 85 % of fire ignitions occurred at less than 500 m from urban areas and 98 % were within a distance of 2 km. Fire ignitions were also located very close to the main roads (70 % at less than 500 m, and 98 % at less than 2 km). Most ignitions were located in agricultural and social/urban areas (60 % and 25%, respectively), and only 15 % in forested or uncultivated areas (8.5 % and 6.5%, respectively). We verified that about 80 % of ignitions occurred at elevations below 500 meters, and that 85 % of fire ignitions originated a burnt area lower than 1 ha, and only 0.3 % of them originated large wildfires with 500 hectares or more. These results emphasise the crucial role of human distribution and activity in the spatial distribution of wildfire ignitions, and can be very useful in fire risk management and in prevention strategies implementation