Where there is road, there is fire (influence): An exploratory study on the influence of roads in the spatial patterns of Swedish wildfires of 2018

English. This study focuses on the Swedish wildfire season of 2018, when the country incurred ten times more than the average burnt area that occurred in previous years. The study aims to address a broad research question: Do roads influence the size of the burned area? This study fills the gap in research on the effects of roads in the spatial patterns of wildfires. Moreover, the research hopes to include the influence of roads in the narrative of wildfire patterns. Among other statistical methods, multivariate regression analysis was ultimately used to answer the research question. Looking at road, landcover, proximity to towns, temperature and fire weather index (FWI), it was found that the parcel sizes of forest and open landscapes influence the average burnt area of a fire. An increase of mean forest area coincides with larger fires, while the inverse is seen for open landscapes. This, in turn, suggests that roads act as fuel breaks and suppression access points by fragmenting forests. A second method that measured the ratio of a fire’s perimeter conforming to the contours of the roads supports the results of the multivariate method above. Of the fires that had edges that conformed to roads, this corresponds to 95% of the total fire area in 2018. An average of 26.7% of the ratio of road conformity was seen in these fires. The increase in conformity percentage led to smaller fire areas. The model created in this method tested what drives the amount of road conformity of fires. The amount of road density and total forest area were statistically significant in driving the conformity of fire perimeter to roads.

Swedish. Studiens fokus är på skogsbränderna i Sverige år 2018, då tio gånger mer markyta påverkades av bränder än genomsnittet under föregående år. Syftet med studien är att undersöka en bred forskningsfråga: har vägar en påverkan på storleken hos den brända ytan i en löpeld? Studien bygger på tidigare forskning om hur spridningen av löpeld påverkas av vägar. Bland olika statistiska metoder valdes slutligen multivariat regressionsanalys för att besvara forskningsfrågan. Genom att ta hänsyn till vägar, marktäcke, närheten till bebyggelse, temperatur samt FWI (Fire Weather Index) kunde ett samband finnas mellan storleken på skogspartier och den genomsnittliga ytan av en brand. En ökning av genomsnittsytan av skogspartier korrelerar med en större brand, medan motsatsen kan ses för öppna landskap. Detta tyder på att vägar dels ökar framkomligheten för brandbekämpning, och dels fungerar som en broms för spridningen av eld genom att dela upp skogen i mindre partier. En annan metod mäter hur stor andel av en brands ytterkant följer en väg, och den här metoden stödjer resultaten från den multivariata metoden. Bränder vars perimeter följde vägar utgjorde 95% av den sammanlagda ytan som brann år 2018. För dessa bränder sammanföll i genomsnitt 26,7% av ytterkanten med en väg. En högre andel kan ses korrelera med en mindre brandyta. Modellen som skapades för den här metoden undersökte vad som driver brändernas anpassning till vägar. Vägtätheten och den totala skogsarealen var statistiskt signifikanta när det gällde hur mycket brandperimetrar följer vägar.

English. Humans have impacted the earth in how lands are changed for us to live on, and for us to create industries using the land. The creation of roads by cutting through the landscapes is needed to move people and products for development. As there is now more evidence that the climate change that we are experiencing is caused by human activities, wildfires are expected to become larger and more frequent through time. By looking at the roads, another mark of human presence, how do these influence the size of wildfires? To make the study possible, smaller parcels were created when roads cut through the landscapes clearly. By looking at the resulting shapes of the 2018 wildfire season in Sweden against the parcels of land, the investigation began. As most of the fires happened in forest land, the study saw that the increase in size of forests tend to have larger fires; the increase of open landscapes, on the other hand, tend to have smaller fires. The study reveals that the quality of burnable materials is essential in determining the sizes of wildfires. By fragmenting the land to smaller parcels, which was made possible by roads, we see that roads do have an influence in the suppression of wildfires. There was also an observation that some of the fires have followed their perimeters to the contours of the roads. This meant that roads could stand as fire breaks preventing the spread of fire to the other side of the road, or that the roads acted as access points for fires to be suppressed by emergency services.