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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/cp-2019-123
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/cp-2019-123
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 14 Oct 2019

Submitted as: research article | 14 Oct 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Climate of the Past (CP).

Coupling between the North Atlantic subpolar gyre vigor and forest fire activity in northern Scandinavia

Tine Nilsen1,2, Dmitry V. Divine3,1, Annika Hofgaard4, Andreas Born5,6, Johann Jungclaus7, and Igor Drobyshev8,9 Tine Nilsen et al.
  • 1Department of Mathematics and Statistics, UiT - The Arctic University of Norway, 9037 Tromsø, Norway
  • 2Department of Geography, Justus-Liebig University of Giessen, 35390 Giessen, Germany
  • 3Norwegian Polar Institute, Fram Centre, 9296 Tromsø, Norway
  • 4Norwegian Institute for Nature Research, 7485 Trondheim, Norway
  • 5Department of Earth Science, University of Bergen, 5020 Bergen, Norway
  • 6Bjerknes Centre for Climate Research, Bergen, 5020 Bergen, Norway
  • 7Max Planck Institute for Meteorology, 20146 Hamburg, Germany
  • 8Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences, 230 53 Alnarp, Sweden
  • 9Chaire industrielle CRSNG-UQAT-UQAM en aménagement forestier durable, Université du Québec en Abitibi-Témiscamingue (UQAT), J9X 5E4 Québec, Canada

Abstract. The circulation strength of the North Atlantic subpolar gyre varies on a range of timescales, it regulates the northwards oceanic heat transport and influences weather and climate over Scandinavia. We test the hypothesis that persistent atmospheric circulation anomalies favorable for extensive forest fire activity in the northern Scandinavian boreal region are predominantly associated with weaker subpolar gyre strength on subannual timescales. We included both winter and summer drought as important precursors for forest fire occurrence in the boreal region. Three ensemble members of climate model simulations covering the time period 850–2005 AD are considered. Years of widespread and severe drought in northern Scandinavia are identified using the monthly drought code as a summer-drought indicator, and winter drought is identified as the 5th percentile of coldest and driest winters. The statistical significance of anomalous ocean- and atmospheric circulation is tested for these years, both during and prior to the main fire season.

Analysis of the ensemble of three simulations did not yield a generalized result, hence the hypothesis cannot be confirmed for subannual timescales. For the three simulations we find respectively that the fire-prone years are associated with subpolar gyre circulation that is on average stronger, weaker or insignificantly changed compared with the mean state. The 5th percentile of most extreme dry and cold winters has a strong relation to the winter North Atlantic oscillation (NAO), but not with the gyre circulation state. We find a number of extremely cold/dry winters occurring during the Little Ice Age (LIA, 16th–19th centuries AD), and infer that winter drought may have played a significant role in promoting forest fire activity at this time.

Our results highlight the importance of resolving the past fire seasonality in the northern Scandinavian domain, and developing compound drought indicators for winter and spring.

Tine Nilsen et al.
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Short summary
Using a set of three climate model simulations we cannot find a consistent relationship between atmospheric conditions favorable for forest fire activity in northern Scandinavia and weaker ocean circulation in the North Atlantic subpolar gyre on seasonal timescales. In the literature there is support of such a relationship for longer timescales. With the motivation to improve seasonal prediction systems, we conclude that the gyre circulation alone does not indicate forthcoming model drought.
Using a set of three climate model simulations we cannot find a consistent relationship between...
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