Effect of climate change on lightning induced forest fires in Austria

Increasing temperatures, due to climate change lead to more evapotranspiration which increases the possibility of severe drought periods. These trends enhance the risk of wildfire hazards even in humid regions like the Alps. Further, possible changes in the occurrence of thunderstorms can modify the ignition danger of lightning induced wildfires. This study aims to investigate the effect of climate change on the probability of wildfires ignited by lightnings including possible shifts in lightning probability for Austria. The full analysis is performed on a 1x1 km grid over Austria. Fire ignition danger and drought periods are approached by computing the Fine Fuel Moisture Code (FFMC). Noon temperature and windspeed for the FFMC are estimated by a spatio-temporal GAM (generalized additive model) with a geographic varying cyclic B-spline. The occurrence of lightnings is approached by the Showalter Index, which is validated with data from the Austrian Lightning Detection and Information System (ALDIS) for the period 2011 to 2020. For the historical weather conditions the Spartacus dataset is used for the period 1981-2022. Regarding the future development, five different climate projections are compared. The historical period showed on average no trend for days with high FFMC values (> 91) for Austria, but already 13% of the study area have a significant positive trend (tested by Mann-Kendall trend test). The trend is even more evident for the climate projections, which show a significant increase in days with FFMC values > 91 for 99% of the study area, with a sharp increase starting about 2050. Possible alterations in thunderstorm activity will strengthen the danger of forest fire ignitions of wildfires in Austria and are posing an increasing threat for forest management and society.