Abstract
Severe lightning flashes, 120,000 a year or four times more than in the average year, started around 300 fires in each of the three years of 2004, 2005, and 2007 but the burnt area of each year differed considerably. The burnt areas in 2004 and 2005 were the largest and the third largest in the last 55 years (1956-2010), respectively; the burnt area in 2007 was smaller than the average 3,541 km2. Overall, a comprehensive understanding of active forest fires in severe lightning years in Alaska was achieved based on various fire characteristics including the newly introduced “number of live fires” and “daily fire activity by hotspots” from NASA. These fire characteristics established the fact that severe lightning ignited Alaska's forests in June and July, and that most of the large fires in 2004 and 2005 started and lasted until August. Large numbers of live fires became active during drought and high-air-temperature conditions, which increased the burnt area in 2004. In 2005, continuous precipitation started from June but a large burnt area was also created by a very active forest fire period in August. The burnt area in 2007 was not so large due to continuous precipitation from the beginning of June.
