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Low level jet and wildfire warning in Croatia

Wildfires in Croatia, particularly at mid-Adriatic coast and islands, are part of Adriatic landscape. The native Mediterranean trees and plants have evolved and adapted to fire environment. Some of the fires showed their disastrous impact not only through the destruction of the vegetation, but also through material damage and human sacrifice. The forest fire analysis in Croatian earlier studies was based on weather condition analysis of typical strong winds prevailing on the Adriatic: bura (NE), jugo (SE) and maestral (NW). In three wildfire cases referred to mentioned wind types, a characteristic vertical wind profile was observed with maximum wind speed at 500-700 m a. g. l. and abrupt speed decrease above followed by change in wind direction. If the maximum wind speed in the lower troposphere exceeds 12 m/s, it is classified as a low level jet (LLJ). LLJ is a very important phenomenon in meteorology because it can have a strong influence on dynamic processes in the atmosphere. Research in the United States found that a fire with turbulent behaviour may sometimes develop immediately before the cold front passage. Therefore, the aim of this study is to investigate the connection of the cold front in synoptic scale and LLJ in mesoscale with emergence and spread of large wildfires in the Adriatic. The large wildfire is defined by the burned area greater than 500 ha. Six synoptic situations with nine large wildfires in the mid-Adriatic from July to September in the period 2001-2011 were selected for the research. Each fire comprised burned area between 850 and 5600 ha. The vertical wind profiles at the fire locations were simulated by the ALADIN/HR mesoscale model. In the considered weather situations all the fires started before the cold front passage and were associated with severe turbulence below the LLJ. Therefore, in the high fire risk situations in Adriatic, the cold front passage and LLJ forecasts could be used as additional warning indicators. Recognizing these additional critical weather conditions during wildfires could be of great help in alerting firefighters to standby. This approach would be beneficial in wildfire natural and material damage reduction as well as in human lives protection.

fire weather ; wildfire ; low level jet ; Croatia

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