Recent Active Forest Fires and Fire Weather in Alaska

Recent weather conditions under rapid climate change will greatly affect each process in forest fire, such as ignition by lightning, extinction, smoldering, rate of fire spread, crown fire, spotting, and other process. Forest fire behaviors are usually not so simple and most of them are strongly related to weather and climate. In this paper, forest fire processes in Alaska are carefully examined to explain background of recent active forest fires in Alaska. Forest fire behavior in 2004 was firstly analyzed simply because total burn area in 2004 was the largest since 1956 and number of lightning flashes was the second largest since 2000. In 2004, wildfires burned 26,700km² in Alaska and nine individual fires exceeded 1,000km² in size. From these large fires, the author tried to extract critical fire expansion processes under so-called fire weather in Alaska by analyzing various data. Analysis results showed: most of fires with large burnt area were ignited during second lightning period of several days in mid June when upper level ridge formed over Alaska. First remarkable fire activity after ignition by lightning started in rate June and highest peak of fire activity was observed in early July. Weather conditions during fire active period could be defined as fire weather in Alaska. Fire weather conditions in around highest fire peak at Fairbanks and its vicinity were: maximum air temperature>25℃, wind speed>4.5m/s, wind direction≒60°(ENE), relative humidity≒30~40% and about 30-day drought from early June. Fire weather conditions in other fire periods in July and August were also clarified.