Historic Spatial Patterns of Storm-Driven Compound Events in UK Estuaries

Abstract

Compound estuarine flooding is driven by extreme sea-levels and river discharge occurring concurrently, or in close succession, and threatens low-lying coastal regions worldwide. We hypothesise that these drivers of flooding rarely occur independently and co-operate at sub-daily timescales. This research aimed to identify regions and individual estuaries within Britain susceptible to storm-driven compound events, using 27 tide gauges linked to 126 river gauges covering a 30-year record. Five methods were evaluated, based on daily mean, daily maximum, and instantaneous 15-min discharge data to identify extremes in the river records, with corresponding skew surges identified within a ‘storm window’ based on average hydrograph duration. The durations, relative timings, and overlap of these extreme events were also calculated. Dependence between extreme skew surge and river discharge in Britain displayed a clear east–west split, with gauges on the west coast showing stronger correlations up to 0.33. Interpreting dependence based on correlation alone can be misleading and should be considered alongside number of historic extreme events. The analyses identified 46 gauges, notably the Rivers Lune and Orchy, where there has been the greatest chance and most occurrences of river-sea extremes coinciding, and where these events readily overlapped one another. Our results were sensitive to the analysis method used. Most notably, daily mean discharge underestimated peaks in the record and did not accurately capture likelihood of compound events in 68% of estuaries. This has implications for future flood risk in Britain, whereby studies should capture sub-daily timescale and concurrent sea-fluvial climatology to support long-term flood management plans.

A New Method to Compile Global Multi-Hazard Event Sets

“…Here, the extreme wind event is likely a storm that is paired with storm surge and/or extreme precipitation, commonly referred to as a compound flood. Various research has shown that these compound floods occur most frequently as a consequence of European winter storms 54,55 , however, they can also occur during summer with devastating impacts, as has been observed during the July 2021 UK floods 56 . Likewise, floods are prominent in Bangladesh, in a flood to flood hazard pair.…”

A new method to compile global multi-hazard event sets

“…Here, the extreme wind event is likely a storm that is paired with storm surge and/or extreme precipitation, commonly referred to as a compound flood. Various research has shown that these compound floods occur most frequently as a consequence of European winter storms 54 , 55 , however, they can also occur during summer with devastating impacts, as has been observed during the July 2021 UK floods 56 . Likewise, floods are prominent in Bangladesh, in a flood to flood hazard pair.…”

MYRIAD-HESA: A New Method to Generate Global Multi-Hazard Event Sets

“…Here, the extreme wind event is likely a storm that is paired with storm surge and/or extreme precipitation, commonly referred to as a compound ood. Various research has shown that these compound oods occur most frequently as a consequence of European winter storms 53,54 , however, they can also occur during summer with devastating impacts, as has been observed during the July 2021 UK oods 55 . Likewise, oods are prominent in Bangladesh, in a ood to ood hazard pair.…”