Abstract
Simple, basic analyses were carried out using two data sets of lightning-caused forest fires and lightning strikes. Recent fire data for 14 years and lightning data for 11 years were analyzed. The analysis clearly showed recent change in the occurrence of forest fires and lightning in Alaska.
The recent situation may be summarized as follows :
1. Average annual burnt area from 1986 is 3464km2, 1. 5 times the long-term average of the 44 years from 1956. This may be due to the effect of so-called global warming.
2. Relatively small fires with burnt areas under 1km2comprise about 70% of the total fire occurrence. The average burnt area per fire is 18km2.
3. A small number of large fires dominate the total annual burnt area. Fire size class of from 100 to 1000km2 covers burnt areas of about 1720km2. Seven fires of this class occur annually and comprise half of the annual burnt area.
4. Fires in Alaska occur from the middle of May till the middle of August. Severe forest fires occur for about two weeks from the end of June.
5. Usual fire occurrence is about 3. 6 fires/day. In severe fire years, fire occurrence has reached about 38 fires/day.
6. Lightning occurrence has two peaks but lightning-caused forest fire occurrence shows only one peak. This difference may be due to the effect of rainfall on forests.
