Abstract
In 2004, many large-scale fires occurred in Alaska and the burned area encompassed about 26,700 km2. This was the largest burned area since 1956, and combined with an additional 19,000 km2 burned in 2005 (third-largest fire year), the total burned area comprised about 10% of the Alaskan boreal forest in just two years. To clarify the background of the many large-scale fires in 2004, spatial and temporal analyses using various data were performed in this paper. The derived results allow the following conclusion. Dry and warm weather conditions with strong persistent winds are crucial for fires. In 2004, easterly winds from Canada caused two daily hotspot peaks in late June and late August; one daily hotspot peak in mid-July was caused by southwesterly winds from Bethel or the Bristol Bay. These persistent winds lasted for about one week and promoted fire expansion. The above wind conditions in June and August were caused by the development of a high-pressure system over the Beaufort Sea under a persistent blocking ridge over Alaska.
