PARENT SESSION
Contributed Oral Session 117: Biodiversity: Climate and Environmental Effects
Thursday, August 11, 8:00 AM - 11:30 AM, Meeting Room 519 A, Level 5, Palais des congrès de Montréal

Synoptic scale atmospheric circulation and summer drought variability of the past three centuries, Boreal Canada.

Girardin, Martin Phillipe^*,1, Tardif, Jacques¹, Flannigan, Mike², Bergeron, Yves³, ¹ Centre for Forest Interdisciplinary Research (C-FIR), Winnipeg, Manitoba, Canada² Great Lakes Forestry Centre, Sault Ste Marie, Ontario, Canada³ Groupe de recherche en écologie forestière inter-universitaire (GREFI), Montréal, Québec, Canada

ABSTRACT- Many fire history studies across boreal Canada report a general decrease in forest fire frequency since 1850. This work intends to provide empirical evidences for the causes of this shift. Five independent multicentury reconstructions of the July Canadian Drought Code and one reconstruction of mean July to August temperature were developed using a network of 120 well-replicated tree-ring chronologies from 13 species covering the portion of the eastern Boreal Plains to the eastern Boreal Shield of Canada. The reconstructions were conducted using 52 time varying reconstruction sub models that explained up to 50% of the regional drought variance during the period 1919-1984. Spatial correlation fields on the six reconstructions and on a rectangular matrix of 90 multicentury tree-ring chronologies revealed that the meridional component of the climate system from central to eastern Canada increased since 1850. Using 500-hPa geopotential height and wind composites, we interpreted this zonal to meridional transition as a response to an amplification of planetary waves flowing over the eastern North Pacific onto boreal Canada, from 1851 to 1940. Composites with NOAA global extended reconstructed sea surface temperatures (SST) indicated a coupling between the meridional component and tropical and North Pacific SST for a period covering at least the past 150-years, supporting previous findings of a summertime global ocean-atmosphere-land surface coupling. This change in the global atmospheric circulation could be a key element toward understanding the observed temporal changes in the forest fire frequency. Over 36% of the variance in the Boreal Shield seasonal area burned (period 1959-1998) can be accounted for by the zonal and meridional atmospheric circulation components defined in this work.

Key words: Dendrochronology, drought reconstruction, climate change, forest fire frequency