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°C since 1830 in Yakutsk, Sakha. In Yakutsk and in interior Alaska, the rate of warming increased notably in the 1970' 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.
Surface flash over a napped fabric is theoretically investigated. A mathematical model is presented to predict the surface flash velocity as a function of nap density, a governing parameter of the phenomenon. The model is an extension of a premixed-gas theory and considers the pyrolysis of fibers and the heat loss to the surroundings. The activation energy asymptotics (AEA) technique is applied to obtain an analytical solution of the model. The model solution correctly reproduced the following two important experimental observations:(1) the dependence of surface flash velocity on the nap density, that is, V0 ∼ ρn0 for small ρn , and V0 ∼ ρn-1 for large ρn , where V0 is the surface flash velocity and ρn the nap density ; (2) the existence of the critical nap density above which surface flash does not occur.
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