Linking past flood frequencies in Norway to regional atmospheric circulation anomalies

Authors

  • Eivind N. Støren,

    Corresponding author
    1. Department of Earth Science, University of Bergen, Norway
    2. Bjerknes Centre for Climate Research, Allégt. 55, 5007 Bergen, Norway
    • Bjerknes Centre for Climate Research, as above.
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  • Erik W. Kolstad,

    1. Bjerknes Centre for Climate Research, Allégt. 55, 5007 Bergen, Norway
    Current affiliation:
    1. StormGeo, Nordre Nøstekaien 1, Bergen, Norway
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  • Øyvind Paasche

    1. Bjerknes Centre for Climate Research, Allégt. 55, 5007 Bergen, Norway
    Current affiliation:
    1. Department of Research Management, University of Bergen, Norway
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Abstract

Analysis of two continuous, high-resolution palaeo-flood records from southern Norway reveals that the frequency of extreme flood events has changed significantly during the Holocene. During the early and middle Holocene, flood frequency was low; by contrast, it was high over the last 2300 years when the mean flood frequency was about 2.5–3.0 per century. The present regional discharge regime is dominated by spring/summer snowmelt, and our results indicate that the changing flood frequency cannot be explained by local conditions associated with the respective catchments of the two lakes, but rather long-term variations of solid winter precipitation and related snowmelt. Applying available instrumental winter precipitation data and associated sea-level pressure re-analysis data as a modern analogue, we document that atmospheric circulation anomalies, significantly different from the North Atlantic Oscillation (NAO), have some potential in explaining the variability of the two different palaeo-flood records. Centennial-scale patterns in shifting flood frequency might be indicative of shifts in atmospheric circulation and shed light on palaeo-pressure variations in the North Atlantic region, in areas not influenced by the NAO. Major shifts are found at about 2300, 1200 and 200 years ago (cal. a BP). Copyright © 2011 John Wiley & Sons, Ltd.

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