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ŠUMARSKI LIST 9-10/2023 str. 70     <-- 70 -->        PDF

2019), and in the short term, time drives fire behavior and spread (Wotton et al., 2007). Flannigan et al. (2016) state that fuel moisture is time dependent. The condition of the plant cover during the growing season is determined by the intensity and frequency of the dry season. The distribution and amount of precipitation affect the increase in the humidity of the fuel material, and thus the decrease in the risk of fire and vice versa (Vučetić, 2001; Ćurić et al., 2013). Heikkilä et al. (2007) state that the moisture content of the fuel is a very important condition for combustion. Many authors in their studies (Dimitrakopoulos et al., 2001; Aguado et al., 2007) state that moisture content was the most significant factor affecting the flammability of Mediterranean forest fuels. Garcia et al. (2008) they state the moisture content of the fuel is correlated with the ignition and spread of fire. Xystrakis et al. (2014) believe that the rate at which fuel dries depends on air humidity and temperature. Fuel material with reduced moisture content is suitable for the occurrence and spread of forest fires (Vasić, 1992; Živanović, 2017; Živanović et al., 2018). If the moisture content is high enough, the amount of available combustible material will decrease and thus the risk of ignition (Burgan, 1979). Gaulton et al. (2013) state that fuel moisture is an important indicator of fire risk. Fuel moisture content is a critical parameter in predicting fire behavior (Zhenxing et al., 2017) and is largely determined by precipitation and air temperature. Živanović (2012) states that the value and variability of climatic elements indicate when and to what extent there is a danger of the occurrence and spread of forest fires. Wotton (2009) claims that weather conditions primarily determine the severity and strength of a forest fire.
The aim of this work is to determine the areas and periods of increased risk of forest fires based on the climatic conditions on northeastern Serbian teritory.
MATERIALS AND METHODS
MATERIJALI I METODE
Northeastern Serbia is a geographic area between 21o40´ and 22o46´ east latitude and 43o20´ and 44o42´ north longitude. The forested area of northeastern Serbia is 3014.79 km2 or about 42.28% of the territory (total area 7130 km2), and deciduous species dominate (beech, oak, hornbeam). Winters in the area of northeastern Serbia are short and cold, and summers are warm. According to Keppen’s climate classification system (Wladimir Köppen, 1846–1940), the climate formula for Negotin is Cfs’’w’’ax, Zaječar Cfs’’w’’bx and Crni Vrh Cfwbx, period 1951-2010. The location of the area of northeastern Serbia is shown in Figure 1.
Data from ground meteorological measurements from three meteorological stations in the area of northeastern Serbia were used to analyze the change in climate conditions (Figure 1). Thresholds of air temperature, amount of precipitation and air humidity in the period 2009-2022. were calculated from the common base period of 1961-1990. Data series are complete (i.e. no missing values). The data were retrieved from the Republic Hydrometeorological Service of Serbia (RHSS, 2023)
The distribution of moisture throughout the year can be determined by a modified version of Thornthwaite’s evapotranspiration index (Thornthwaite, 1948):
                M = (PR) – F          (1)
where:
M – Monthly moisture index
P – Total monthly precipitation (cm)
R – Total monthly days with precipitation, and
F – Evapotranspiration factor.
The evapotranspiration factor can be represented by the formula:
                                (2)
where:
T – Mean monthly air temperature (oC), and
L – Mean monthly day length (h).