最近の北方林での大規模森林火災と気候変動: アラスカとサハでの森林火災と気象データによる考察

摘要

北方林，通称タイガは，世界の森林面積の1/3を占 め，夏期の間，平均で300m以下と降雨量が少なく， 火災の危険性が高く，種々の観点からの研究がなされ ている。Campbellらは，最近の気候変動と連動した 暖かい乾燥した夏の傾向から，北方林での火災の数と 規模の増加を予測している。%This paper describes recent forest fire and weather trends in Alaska, North America and Sakha, Far East Siberia. Both regions have reported large forest fires in recent years. The increased burning is potentially linked to climate change. Mean air temperature increased about 3℃ since 1830 in Yakutsk, Sakha. In Yakutsk and in interior Alaska, the rate of warming increased notably in thel970's. At the same time, there was a gradual decreasing trend in precipitation. Forest fire histories from the mid -1950's in Alaska and Sakha show that mean annual area burned increased notably in the 1990's. A warmer, drier climate greatly increases boreal forest flammability. Under such climate conditions, large forest fires occurred near Yakutsk, Sakha, in 2002. In 2004 and 2005, wildfires burned 26,700 and 19,000 km2 respectively in Alaska. Total burned area in 2004 was the largest since record-keeping began in Alaska in 1956 equal to 10% of Alaska's boreal forest area. To identify potential causes of these recent severe fires, a half century of forest fire and weather data were analyzed. Tables show trends of forest fires and weather before and after 1990. June weather was the most important factor in predicting forest fire activity in both Alaska and Sakha. However, forest fires in Alaska were primarily associated with warm June temperatures while forest fires in Sakha were mainly associated with precipitation. The strong correlation between fire activity and climate suggests that global warming may bring more frequent large-scale fire events to the boreal forest.