Fire Weather Anomalies Previous and During Large Forest Fires—A Comparison Between Mt. Carmel and Judean Hills

The Mediterranean region is a highly fire-prone ecosystem with a long fire history, aggravated by the prevailing climate conditions (hot and dry summers) coupled with intensive land use. All forest fires in Israel are manmade, however, the weather conditions after ignition are crucial for its propagation. Given the recent increase in fire activity, the study explores Medium Time Scales (seasonal to annual) climatic variables affecting fire occurrences in Mt. Carmel and the Judean hills region, two ‘hotspots’ of frequent and devastating forest fires. The main climate variables for rapid forest fire propagation are very low relative humidity and above normal air temperature together with strong winds. Meteorological data for 1988–2019 were collected at two stations representing the weather conditions on Mt. Carmel and the Judean hills. During that period, data for all wildfires larger than 50 ha, on both sites, were obtained from the ‘Israel Fire and Rescue Services’. For each fire event, data included burnt area, exact location, date, fire duration and daily maximum temperature, daily minimum relative humidity, daily maximum wind speed and the wind direction during the maximum wind speed. The burnt area size was correlated with of relative humidity and air temperature departures, from the long-term average at the same time and location. Calculations were done for the day of the fire occurrence (day = 0) and for each day during the previous week (day =  −7 to day =  − 1). In Mt. Carmel, most forest fires (>50 ha) occurred in autumn (September–November), whereas in the Judean hills they occurred in summer (May–October). In summer, temperatures are at their annual maximum, a constant moderate sea breeze blows, and the fuel is relatively dry. However, while in Judean hills, relative humidity is at its annual minimum, on Mt. Carmel, in this period, relative humidity is at its annual maximum. This difference in the relative humidity regime between these two regions, apart from each other only by 120 km, is the leading cause of the difference in the timing of major forest fires. This method is already used for alerting of dangerous weather conditions that may result in a devastating forest fire.