Extreme forest fires and predictive power of Fire Danger Indices: A deepening in the Alpine region

At alpine scale, the efficiency of fire danger forecast services, prevention activities and fire fighting actions has significantly improved in the last decades. Ongoing trends show a strong decrease both in the overall frequency of forest fires and in the mean extension of burnt area per single fire occurrence. In spite of that, forest fires still represent one of the main threats impacting alpine forests. In the next future, ongoing climate changes could play a relevant role in influencing both the frequency, the geographical patterns and the regimes of fires in the Alpine area. Moreover, they could play a relevant role in inducing the occurrence of big or extreme fires. As a consequence, great efforts should be made to monitor the evolution of fire patterns in the Alps and to identify fire danger indexes highly performing in the Alpine region. Two Alpine Space projects (MANFRED and ALP FFIRS) recently co-operated on these topics. This paper synthesizes the results of the collaboration, aiming mainly at (1) understanding if extreme fire occurrences are significantly influenced by meteo-climatic conditions and (2) identifying the Fire Danger Indices having the best performance in the prediction of extreme occurrences. In the framework of this joint action, a pan-alpine dataset of fires has been generated (more than 82.000 fires, about 26.000 occurrences in the time span 2000 - 2009). The dataset maps the points of ignition and describes each event with a standard set of attributes. Extreme fires (99th percentile of the attribute Total Burnt Area) occurred in the period 2003-2009 were identified and used to test a selection of about 19 Fire Weather Indices, with non-parametric statistics, to investigate their ability in distinguishing between fire/non fire days and between common fire conditions and extreme fire conditions.