Convergent human and climate forcing of late-Holocene flooding in northwest England

This is a Preprint and has not been peer reviewed. The published version of this Preprint is available: https://doi.org/10.1016/j.gloplacha.2019.102998.

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Authors

Daniel Schillereff , Richard Chiverrell, Neil Macdonald, Janet Hooke, Katharine Welsh, Gayane Piliposyan, Ian W Croudance

Abstract

Concern is growing that climate change may amplify global flood risk but short hydrological data series hamper hazard assessment. Lake sediment reconstructions are capturing a fuller picture of rare, high-magnitude events but the UK has produced few lake palaeoflood records. We report the longest lake-derived flood reconstruction for the UK to date, a 1500-year record from Brotherswater, northwest England. Its catchment is well-suited physiographically to palaeoflood research, but its homogeneous, dark brown sediment matrix precludes visual identification of flood layers. Instead, an outlier detection routine applied to high-resolution particle size measurements showed a >90% match, in stratigraphic sequence, to measured high river flows. Our late-Holocene palaeoflood reconstruction reveals nine multi-decadal periods of more frequent flooding (CE 510-630, 890-960, 990-1080, 1470-1560, 1590-1620, 1650-1710, 1740-1770, 1830-1890 and 1920-2012), and these show a significant association with negative winter North Atlantic Oscillation (wNAO) phasing and some synchrony with solar minima. These flood-rich episodes also overlap with local and regional land-use intensification, which we propose has amplified the flood signal by creating a more efficient catchment sediment conveyor and more rapid hillslope-channel hydrological connectivity. Disentangling anthropogenic and climatic drivers is a challenge but anthropogenic landscape transformation should evidently not be underestimated in palaeoflood reconstructions. Our paper also demonstrates that flood histories can be extracted from the numerous lakes worldwide containing organic-rich, visually homogeneous sediments. This transformative evidence base should lead to more reliable assessments of flood frequency and risks to ecosystems and infrastructure.

DOI

https://doi.org/10.31223/osf.io/4jrwh

Subjects

Earth Sciences, Environmental Sciences, Geography, Geomorphology, Physical and Environmental Geography, Physical Sciences and Mathematics, Social and Behavioral Sciences

Keywords

Lake sediments, flood hazard, Human activity, North Atlantic Oscillation, Paleofloods, Solar forcing

Dates

Published: 2019-08-12 18:34

Last Updated: 2019-08-13 12:44

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License

CC BY Attribution 4.0 International

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