PARENT SESSION
Symposium 1: The boreal forest and global change
Organized by: EA Johnson, K Miyanishi, and K Ruckstuhl
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 517 A, Level 5, Palais des congrès de Montréal
Patterns of wildfires in the North American boreal forest as related to climate.
Macias, Marc*,1, Johnson, Edward2, 1 University of Helsinki, Helsinki, Finland2 University of Calgary, Calgary, AB, Canada
ABSTRACT- Large lightning-caused fires in the boreal forest account for most of the area burned and are therefore the main determiners of the age mosaic of the landscape. Such fires occur when positive mid-troposphere pressure anomalies persist during the fire season. The coupling between surface weather and mid-troposphere circulation anomalies provides an explanation for these periods of major fire activity. These positive mid-troposphere events have temporal scales of days to weeks, allowing for long periods with extreme fuel drying, and spatial scales from hundreds to a few thousand kilometres, reducing fuel moisture over large areas. Mid-troposphere anomalies occur in atmospheric waves with geographically fixed nodes and antinodes, which constitute recurring and persistent, large-scale patterns of pressure and span vast geographical areas. Thus, the presence of a positive anomaly (high pressure system) over an area is caused by events occurring at long distances upstream in the atmospheric wave. Our results define eight major centers of fire action in the North American boreal forest between 1959 -1999. These centers of action are related to the mid-troposphere anomalies called the Pacific North America Pattern and the North Atlantic Oscillation and the position of their low pressure centers in the Pacific, Atlantic and Arctic Oceans. Climate changes may cause different locations of the fire areas through the change in location of ridges and troughs in the mid-troposphere circulation and changes in their frequency.
Key words: atmospheric circulation, lightning-caused fires, mid-troposphere anomalies, extreme fire weather