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Multicentury reconstruction of the Canadian Drought Code from eastern Canada and its relationship with paleoclimatic indices of atmospheric circulation
Authors:Email author" target="_blank">M-P?GirardinEmail author  J?Tardif  M?D?Flannigan  Y?Bergeron
Institution:(1) Centre for Forest Interdisciplinary Research (C-FIR), University of Winnipeg, 515 Avenue Portage, Winnipeg, Manitoba, R3B 2E9, Canada;(2) Canadian Forest Service, 1219 Queen St East, Sault Ste Marie, Ontario P6A 2E5, Canada;(3) Groupe de recherche en écologie forestière inter-universitaire (GREFI), Université du Québec à Montréal, C.P. 8888, Succ. Centre-Ville, Montréal, Québec, H3C 3P8, Canada;(4) Department of Botany, University of Manitoba, 505 Buller Building, Winnipeg, Manitoba, R3T 2N2, Canada
Abstract:Inter-annual and -decadal scale variability in drought over the Abitibi Plains ecoregion (eastern Canada) was investigated using a 380-year dendroclimatic reconstruction of the Canadian Drought Code (CDC; July monthly average) i.e., a daily numerical rating of the average moisture content of deep organic layers. Spectral analyses conducted on the reconstructed CDC indicated a shift in spectral power after 1850 leading toward a reduction in interdecadal variability and an increase in interannual variability. Investigation on the causes for this shift suggested a decrease in North Pacific forcing after the mid-nineteenth century. Cross-continuous wavelet transformation analyses indicated coherency in the 8–16 and 17–32-year per cycle oscillation bands between the CDC reconstruction and the Pacific Decadal Oscillation (PDO) prior to 1850. Following 1850, the coherency shifted toward the North Atlantic Oscillation (NAO). Principal component analysis conducted over varying time windows reaffirmed that the Pacific forcing was restricted to the period about 1750–1850. Prior to and after this period, the CDC was correlated with the NAO. The shift around 1850 could reflect a northward displacement of the polar jet stream induced by a warming of the sea surface temperature along the North Pacific coast. A northward displacement of the jet stream, which inhibits the outflow of cold and dry Arctic air, could have allowed the incursion of air masses from the Atlantic subtropical regions.
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