The term forest fire risk means the existence of such conditions that would make possible the occurrence of a fire in the forest environment. The base for the effectiveness of a forest fire protection system is the evaluation of the forest fire risk followed by adequate organization of the system. This article presents methods for determination of the forest susceptibility to fire known as potential forest fire risk. The below presented methods were developed by Forest Research Institute as the results of the projects commissioned by the General Directorate of State Forests. The forest fire risk category and stand flammability classes are the methods included here. The forest fire risk category was elaborated already in 1975 for the first time. Until today, after the last modification in 2008, it is the fundamental document for the polish forest fire protection system. The purpose of this modification was to increase the determination accuracy of the fire risk category of all polish forest, regardless of its ownership type and at the different administrative level. The categorization method, however, doesn’t reflect the fire risk in micro scale. The attempt to solve that problem was made in 2018 while developing the methodology of stand flammability classes. It was assumed that ground cover fuel models will be developed for the most flammable forest habitat types including ground cover types, dominant species, age class and geographical localisation.
The weather conditions determine the dynamic forest fire risk. In Poland, the dynamic forest fire risk is calculated using a method elaborated at the Forest Research Institute. The forest fire risk degree (4-level scale) is calculated every day at 9:00 am and at 1:00 pm during the fire season (1.03 till 30.09) for 60 prognostic zones selected on the basis of stand and climatic conditions. 97% of all annual forest fires occur during the fire season. Surface fires are a significant part of the fires (90%) and occur in forest stands where pine is the dominant species. The purpose of the research was to prepare a new method of forecasting forest fire risk, which would enable a more precise method of evaluation of the risk of an outbreak of fire in relation to the existing and forecast meteorological conditions in forests. The results obtained during testing of this method indicate a high accuracy in forecasting fire risk and a satisfactory precision of formulae for calculating moisture content of pine litter.
The assumptions of the new method included:
–possibility of determining the actual risk of fire for the given area, being the average for all measurement points located on the terrain equally those in which the moisture content measurement of litter has not been performed,
–possibility of forecasting the risk of forest fire for the afternoon in the morning hours of the given day,
–possibility of forecasting fire risk for the following day,
–forecasting moisture content of litter for the afternoon and of the given day and for the following day,
–drawing up a method enabling limitation of operational costs of fire prevention system.