engleski

Numerical modelling of weather conditions during the wildfires

In Croatia, forests cover 44% of the area, and the mean annual burned area is about 10, 000 ha mainly on the Adriatic coast and islands. For early warning of fire brigades, it is important to know the weather situation that precedes the wildfires. Two large wildfires were intentionally caused on the Pelješac Peninsula on the southern Croatian coast on 20/21 July 2015 at night and were completely extinguished in mid-August. The aim of this study is to research weather conditions and vertical structure of atmosphere that led to the begging of wildfires by using the meteorological data and ALADIN/HR numerical simulations model. Fires preceded the very dry and hot weather (25 days without rain and seven consecutive days with maximum daily air temperature above 34°C). The absolute maximum temperature of 38.8°C on the peninsula of Pelješac was measured in the first day of the fire, and the next night minimum daily temperature was 30°C. During the wildfires slightly lower air pressure prevailed on the southern Adriatic, the warm air was up to 850 hPa and relative humidity was around 40% during the day. Few hours before fires wind gusts reached 12 m/s. Canadian forest fire weather index (FWI) showed high risk of wildfire until 26 July 2015 and initial spread index (ISI) indicated the worst possible forest fires - fire crown. ALADIN/HR model predicted weak wind up to 5 m/s, decreasing air temperatures with height and almost neutral air stratification in the lower troposphere during the fire. The rapid spread of the fire, which was affected in a short time a large part of the peninsula, favoured very dry dead fuel material of the Mediterranean vegetation and quick lifting of hot air accelerated very steep terrain. Haines index showed high risk of forest fire during the day and moderate risk during nights.

wildfire, Fire Weather Index, vertical wind profile, ALADIN model, Croatia

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