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

TY - JOUR

T1 - Convergent human and climate forcing of late-Holocene flooding in Northwest England

AU - Schillereff, D. N.

AU - Chiverrell, R. C.

AU - Macdonald, N.

AU - Hooke, J. M.

AU - Welsh, K. E.

AU - Piliposian, G.

AU - Croudace, I. W.

PY - 2019/11/1

Y1 - 2019/11/1

N2 - 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 (510–630 CE, 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.

AB - 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 (510–630 CE, 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.

KW - Flood hazard

KW - Human activity

KW - Lake sediments

KW - North Atlantic Oscillation

KW - Paleofloods

KW - Solar forcing

UR - http://www.scopus.com/inward/record.url?scp=85064194681&partnerID=8YFLogxK

U2 - 10.1016/j.gloplacha.2019.102998

DO - 10.1016/j.gloplacha.2019.102998

M3 - Article

AN - SCOPUS:85064194681

SN - 0921-8181

VL - 182

JO - GLOBAL AND PLANETARY CHANGE

JF - GLOBAL AND PLANETARY CHANGE

M1 - 102998

ER -