Abstract
Millennial- and multi-centennial scale climate variability during the Holocene has been well documented, but its impact on the distribution and timing of extreme river floods has yet to be established. Here we present a meta-analysis of more than 2000 radiometrically dated flood units to reconstruct centennial-scale Holocene flood episodes in Europe and North Africa. Our data analysis shows a general increase in flood frequency after 5000 cal. yr BP consistent with a weakening in zonal circulation over the second half of the Holocene, and with an increase in winter insolation. Multi-centennial length phases of flooding in UK and central Europe correspond with periods of minimum solar irradiance, with a clear trend of increasing flood frequency over the last 1000 years. Western Mediterranean regions show synchrony of flood episodes associated with negative phases of the North Atlantic Oscillation that are out-of-phase with those evident within the eastern Mediterranean. This long-term flood record reveals complex but geographically highly interconnected climate-flood relationships, and provides a new framework to understand likely future spatial changes of flood frequency.
Highlights
Millennial- and multi-centennial scale climate variability during the Holocene has been well documented, but its impact on the distribution and timing of extreme river floods has yet to be established
We cannot assume that these long-term record floods and flood patterns will be reproduced in the future, they do hold key knowledge to understand the effect of multi-decadal climate variability on extreme flooding at regional and global scales
The dated fluvial deposits comprise slackwater and boulder berm flood sediments representing individual palaeoflood events, as well as flood units from alluvial floodplain and flood basin environments that record, in some instances, single large floods and changes in the discharge-sediment load over multi-decadal periods. This reveals spatially coherent flood distribution patterns, which are repeated through time, with synchronous and asynchronous episodes of hydrological activity in response to shifts in atmospheric circulation modes associated with Holocene climate variability
Summary
Gerardo Benito[1], Mark G. We present a meta-analysis of more than 2000 radiometrically dated flood units to reconstruct centennial-scale Holocene flood episodes in Europe and North Africa. This long-term flood record reveals complex but geographically highly interconnected climate-flood relationships, and provides a new framework to understand likely future spatial changes of flood frequency. A major achievement in the last decade has been the development of meta-analysis for large databases of 14C-dated Holocene flood units[3] This approach facilitates comparison of probability-based flood series with climate and human impact proxy records, to better constrain the factors that control extreme events, and to inform present and future flood-risk assessment. There is less synchrony of flood periods between regions than in the Mediterranean, suggesting a lower sensitivity to extreme hydroclimatic changes (i.e. lower hydrological variance; Fig. 3d,e)
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