Complementing daily fire-danger assessment using a novel metric based on burnt area ranking

Understanding the relationship between fire and weather has important implications for fire danger evaluations, firefighting and fire management. Fire weather indices are mathematical representations of a suite of meteorological variables that are often used as decision-support tools for evaluating the likelihood of fire on a given day. However, these indices are seldom evaluated for their ability to express a probability in terms of final burnt area, which is a very important fire danger component. We propose a new approach for selecting fire weather indices that represent good proxies for both the probability of fire occurrence on a particular day and of the related final burnt area. The novel performance metric was applied to historical data (11 to 31 years) from four European regions with different fire regimes in Switzerland (Canton Ticino) and Italy (Cilento in Campania, Chilivani and Campidano in Sardinia). The results confirm the suitability of the approach for selecting an appropriate fire weather index for a particular region and for providing insight into the regional meteorological control patterns of fire ignition and spread. For three of the six fire regime types analyzed (Campidano, Cilento and winter fire season in Ticino), the prediction power for burnt area of most indices was generally in accordance with estimates of fire ignition risk. For the remaining case studies, fire ignition and burnt area appear to be controlled by different meteorological or non-climatic drivers. In these cases, the selection of the most suitable index should be based on a cutoff that optimizes the two selection criteria according to local needs. From an operational point of view, this novel approach that includes the burnt area aspect can strongly support decisions on firefighting alert and preparedness as well as requested firefighting strategies.