Іmproving the methodology of natural fire hazard assessment for forested lands based on a risk-oriented approach

An analysis of the combustibility of the forests of «Zhovtneve» State Enterprise was carried out, with the identification of the most fire-prone forests. The distribution of the forest fund plots of each of the researched forestry by classes of natural fire hazard was analyzed. The spatial distribution of the fire density including forest fires as well as wildfires in the 500- meter buffer zone around forest was studied. The article describes a methodology that allows improving the existing methodology for assessing the natural fire hazard of forest lands based on a risk-oriented approach. According to the Kernel density algorithm with the use of desktop GIS systems, a map of the probability of fire occurrence was built. According to the results of the Kernel Density algorithm, the main flammability centers and the density of fires were identified and the territory of the enterprise was divided into classes according to the probability of fires. According to the proposed classification of the fire probability occurrence: low (up to 10.6 cases is the arithmetic average for the entire map); medium (from 10.7 to 28 — 1.01–1.5σ); high (over 28 — over 1.5σ). The integration of the probability of fire occurrence into the scale of natural fire hazard was carried out through the technique of «risk matrices». Thus, the combination of the classes of natural fire hazard classes with the classes of the fire probability occurrence made it possible to obtain an integrated FRS indicator (Fire Risk Score), which includes both: the level of natural fire hazard and the probability of fire occurrence. In order to verify the results, calculations of actual flammability (fire density and flammability by burnt area) were carried out for each class of the national scale of fire hazard and for the FRS classes of each plot. It was found that significant levels of flammability are characteristic only for the first two classes of natural fire hazard (fire density 83.64 cases per 1000 hectares of forests), the flammability of forests with higher natural hazard classes is practically absent, which indicates the need to differentiate the tree stands that are belongs to these two classes. On the other hand, classifying forests with the assignment of points according to FRS revealed an increase in the indicators of forest combustibility and fire density as the FRS indicator increases (at FRS values of 2–3 there are no fires, at FRS values from 4 to 8, combustibility is moderate (from 1.25 to 3.7 cases per 1000 ha), at values above 9 points, the flammability increases sharply and reaches its peak at the FRS value of 13 points (224.5 cases per 1000 ha). Thus, the improved scale based on the risk-oriented approach (fire risk score) more fully reflects the level of danger in the forest based not only on the natural features of the area and fuel complexes characteristics, but also taking into account the spatial location of fire sources and the frequency of fires in each location.