Abstract
AbstractWe analyze trends in compound flooding resulting from high coastal water levels (HCWLs) and peak river discharge over northwestern Europe during 1901–2014. Compound peak discharge associated with 37 stream gauges with at least 70 years of record availability near the North and Baltic Sea coasts is used. Compound flooding is assessed using a newly developed index, compound hazard ratio, that compares the severity of river flooding associated with HCWL with the at‐site, T‐year (a flood with 1/T chance of being exceeded in any given year) fluvial peak discharge. Our findings suggest a spatially coherent pattern in the dependence between HCWL and river peaks and in compound flood magnitudes and frequency. For higher return levels, we find upward trends in compound hazard ratio frequency at midlatitudes (gauges from 47°N to 60°N) and downward trends along the high latitude (>60°N) regions of northwestern Europe.
Highlights
We analyze trends in compound flooding resulting from high coastal water levels (HCWLs) and peak river discharge over northwestern Europe during 1901–2014
Compound flooding is assessed using a newly developed index, compound hazard ratio, that compares the severity of river flooding associated with HCWL with the at‐site, T‐year fluvial peak discharge
We present a new approach to assess compound flood severity resulting from extreme coastal water level and peak river discharge
Summary
There is a considerable body of recent literature on compound flooding, that is, the simultaneous or d‐day lagged occurrence of extreme sea levels and peak river discharges (or extreme precipitation as a proxy for flooding), in Europe (Bevacqua et al, 2017; Bevacqua et al, 2018; Paprotny et al, 2018; Petroliagkis et al, 2016) and globally (Moftakhari et al, 2017; Wahl et al, 2015; Ward et al, 2018; Zheng et al, 2013; Zscheischler et al, 2018). Previous researchers have identified a moderate to strong correlation between high coastal water levels (HCWLs) or storm surges and floods (either pluvial or fluvial) globally (Ward et al, 2018), and regionally across Europe (Kew et al, 2013; Paprotny et al, 2018; Petroliagkis et al, 2016; Reeve et al, 2008; Svensson & Jones, 2001; Svensson & Jones, 2004), the United States (Moftakhari et al, 2017; Sadegh et al, 2018), Australia (Wu et al, 2018; Zheng et al, 2013, 2014), and China (Lian et al, 2013; Tu et al, 2018) They have focused on the joint probability of compound floods (Couasnon et al, 2018; Kew et al, 2013; Moftakhari et al, 2019; Moftakhari et al, 2017; Sadegh et al, 2018; Ward et al, 2018) considering individual drivers and the conditional probability (Bevacqua et al, 2017) of occurrence of river floods given moderate to extreme coastal water levels or surges. These metrics are valuable for risk management and infrastructure design in delta areas (Wu et al, 2018).
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