S.A.M.A de Maat1*, J.G.W. Beemster1 , A.J.F. Hoitink1 , S. Fischer1 , C.B.M. Weijenborg2.
1Hydrology and Environmental Hydraulics Group, Wageningen University and Research, The Netherlands; 2Meteorology and Air Quality Group, Wageningen University and Research, The Netherlands;
* Corresponding author: sander.demaat@wur.nl
Introduction
Extreme weather events, particularly storm surges, pose an increasing risk to coastal communities worldwide due to climate change. In the Netherlands, storm surges, characterized by sudden sea level rise, are primarily caused by extratropical cyclones (ETCs). Research has shown that storm surges are complex natural hazards influenced by a combination of meteorological, oceanographic, and geographic factors. One key meteorological driver is the clustering of serial cyclones (SCC), a phenomenon in which multiple ETCs pass over the same area within a short timeframe. Recent findings by Rantanen et al. (2024) indicate that nearly 50% of extreme sea level events in the Baltic Sea are linked to periods of SCC.
Despite the significant threat storm surges pose to the Dutch coastline, most existing research has focused on single storm surge events. This knowledge gap introduces critical uncertainties in coastal defence planning and flood risk management. Specifically, the extent to which SCC amplifies storm surges and influences extreme water level statistics, such as return periods, remains unclear. These uncertainties are crucial for designing robust coastal protections.
Objective and Methods
This study assesses whether storm surges amplify along the Dutch coastline during clustered events and aims to identify the factors driving this amplification across regions. It addresses a key knowledge gap on storm surge amplification linked to SCC, investigating how these factors heighten the severity and frequency of major events, particularly in low-lying areas like the Netherlands.
To quantify storm surge amplification, its regional variations, impacts on flood metrics, and the role of SCC, we analyse hourly water level data from 10 Dutch tide gauge stations alongside ERA5 meteorological reanalysis data. Storm surge events are extracted from the low-pass filtered residual water levels using the 95th percentile as threshold. Peak water levels are considered clustered if they occur within a three-day window. ETC tracks are derived and six-hourly MSLP fields are analysed while excluding ETCs lasting <24 hours or traveling <500 km to focus on larger systems. Clustering is identified when ETCs pass within two to three days of each other. A statistical model is then applied to assess impacts on flood metrics, incorporating extreme value statistics and mixture models to evaluate how clustering influences return periods and storm surge heights.
Results
Preliminary results indicate that clustered storm surges lead to higher peak water levels across all tidal stations. Return period analysis suggests that in some areas, conventional methods may underestimate the impact of clustering, as clustered storm surges result in higher water levels for given return periods compared to non-clustered events. For example, a return period of 10 years at the Bath (near Belgian border) for clustered storm surges show an increase of 12 cm compared to single storm surge events. Additionally, in southern regions like the Western Scheldt, this signal appears to be stronger than in northern regions like the Wadden Sea. Further analysis is underway to refine these findings, assess regional variations in storm surge amplification, and identifying factors driving the amplification of clustered storm surges.
References
Rantanen, M., Van Den Broek, D., Cornér, J., Sinclair, V. A., Johansson, M. M., Särkkä, J., Laurila, T. K., & Jylhä, K. (2024). The impact of serial cyclone clustering on extremely high sea levels in the Baltic Sea. Geophysical Research Letters, 51(6). https://doi.org/10.1029/2023gl107203
