Linking past flood frequencies in Norway to regional atmospheric circulation anomalies

• Published in: Journal of Quaternary Science
• Main Authors: Støren, Eivind N., Kolstad, Erik W., Paasche, Øyvind
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2011
• Subjects: North Atlantic; North Atlantic oscillation
• Online Access: http://dx.doi.org/10.1002/jqs.1520; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fjqs.1520; https://onlinelibrary.wiley.com/doi/pdf/10.1002/jqs.1520

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.