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Heterogeneous response of circumboreal wildfire risk to climate change since the early 1900s

Authors

  • MARTIN P. GIRARDIN,

    1. Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre, 1055 du P.E.P.S., PO Box 10380, Stn. Sainte-Foy, Quebec, QC, Canada G1V 4C7,
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  • ADAM A. ALI,

    1. Centre de Bio-Archéologie et d'Écologie (UMR 5059 CNRS), Université Montpellier 2, 163 rue Auguste Broussonet, F-34090, Montpellier, France,
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  • CHRISTOPHER CARCAILLET,

    1. Centre de Bio-Archéologie et d'Écologie (UMR 5059 CNRS) & Paleoenvironments and Chronoecology (PALECO EPHE), Université Montpellier 2, 163 rue Auguste Broussonet, F-34090, Montpellier, France,
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  • MANFRED MUDELSEE,

    1. Climate Risk Analysis, Schneiderberg 26, 30167 Hannover, Germany,
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  • IGOR DROBYSHEV,

    1. Université du Québec en Abitibi-Témiscamingue, 445 boulevard de l'Université, Rouyn-Noranda, QC, Canada J9X 5E4,
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  • CHRISTELLE HÉLY,

    1. CEREGE, CNRS UMR 6635, Université Paul Cézanne-Aix-Marseille III, Europôle de l'Arbois, BP 80, 13545 Aix en Provence cedex 4, France,
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  • YVES BERGERON

    1. Université du Québec en Abitibi-Témiscamingue, 445 boulevard de l'Université, Rouyn-Noranda, QC, Canada J9X 5E4
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Martin P. Girardin, e-mail: martin.girardin@rncan.gc.ca

Abstract

We investigated changes in wildfire risk over the 1901−2002 (ad) period with an analysis of broad-scale patterns of July monthly drought code (MDC) variability on 28 forested ecoregions of the North American and Eurasian continents. The MDC is an estimate of the net effect of changes in evapotranspiration and precipitation on cumulative moisture depletion in soils, and is well correlated with annual fire statistics across the circumboreal (explaining 25–61% of the variance in regional area burned). We used linear trend and regime shift analyses to investigate (multi-) decadal changes in MDC and percentage area affected by drought, and kernel function for analysis of temporal changes in the occurrence rates of extreme drought years. Our analyses did not reveal widespread patterns of linear increases in dryness through time as a response to rising Northern Hemisphere land temperatures. Instead, we found heterogeneous patterns of drought severity changes that were inherent to the nonuniformly distributed impacts of climate change on dryness. Notably, significant trends toward increasing summer moisture in southeastern and southwestern boreal Canada were detected. The diminishing wildfire risk in these regions is coherent with widely reported decreases in area burned since about 1850, as reconstructed by dendrochronological dating of forest stands. Conversely, we found evidence for increasing percentage area affected by extreme droughts in Eurasia (+0.57% per decade; P<0.05) and occurrence rates of extreme drought years in Eurasian taiga (centered principally on the Okhotsk–Manchurian taiga, P=0.07). Although not statistically significant, temporal changes in occurrence rates are sufficiently important spatially to be paid further attention. The absence of a linear trend in MDC severity, in conjunction with the presence of an increase in the occurrence rate of extreme drought years, suggest that fire disturbance regimes in the Eurasian taiga could be shifting toward being increasingly pulse dependent.

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