atmosphere 
Article 
Negative Storm Surges in the Elbe Estuary—Large-Scale 
Meteorological Conditions and Future Climate Change 
Corinna Jensen !, Tara Mahavadi ?®, Nils H. Schade !, Ingo Hache ?® and Tim Kruschke !+@ 
' 
Federal Maritime and Hydrographic Agency (BSH), 20359 Hamburg, Germany 
Federal Waterways Engineering and Research Institute (BAW), 22559 Hamburg, Germany 
Correspondence: tim.kruschke@bsh.de; Tel.: +49-40-3190-3210 
Abstract: Negative storm surges in the Elbe estuary can affect shipping as well as shoreline in- 
frastructure. The significant reduction of water level caused by strong offshore winds can lead to 
extreme low water events, which endanger waterfront structures. The current study analyses the 
large-scale meteorological conditions inducing such situations and possible future changes due to 
zlimate change. The analysis is based on tide gauge data from Cuxhaven, atmospheric reanalysis 
data and an objective weather classification approach. It is found that south-easterly wind directions 
in combination with strong gales favour extreme low water events at Cuxhaven. Furthermore, the 
analysis of a single model large ensemble of climate projections shows a significant decrease in the 
frequency of such conditions for the far future (2071-2100). Regarding future global mean sea level 
rise the simulation results of a sensitivity study indicate that water levels during such extreme events 
approximately follow the development of the mean sea level rise. Therefore, our study suggests that 
both meteorological conditions and mean sea levels in a warmer future climate will be less favourable 
tor the occurrence of extreme low water events in the Elbe estuary. 
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Citation: Jensen, C.; Mahavadı, T.; 
Schade, N.H.; Hache, I.; Kruschke, T. 
Negative Storm Surges in the Elbe 
Estuary—Large-Scale Meteorological 
Conditions and Future Climate 
Change. Atmosphere 2022, 13, 1634. 
https: //doi.org/10.3390/ 
atmos 13101634 
Keywords: negative storm tides; negative storm surges; weather types; circulation patterns; climate 
change; Elbe estuary; North Sea; sea level rise; transport; extreme low water events 
1. Introduction 
Strong offshore winds can lead to a significant reduction in the water level in the 
tidally dominated German Bight and adjacent estuaries. Events like these may severely 
restrict transportation along the waterways and could therefore lead to economic loss 
Extremely lowered water levels can also endanger the stability of waterfront structures 
along the shoreline due to pressure imbalance [1]. The port of Hamburg is a very important 
iransit point and the third biggest port in Europe (after Rotterdam and Antwerp) where 
.28.7 million tons of seaborne cargoes were loaded or discharged in 2021 [2]. It is situated 
approx. 107 km inland in the Elbe estuary, which is significantly affected by tides with an 
average tidal range of 3.82 m measured at St. Pauli (close to the harbour) [3]. 
Besides this tidal variability, the occurrence of strong surface-near winds—depending 
on wind direction—significantly alters water levels in the Elbe estuary. Generally speaking, 
ıf wind direction roughly matches (opposes) the stream direction of the Elbe river out of the 
estuary, water levels are reduced (increased) relative to what would be expected from the 
tidal influence only. The phenomenon of wind-induced reduction of water levels during 
tidal low water can be referred to as storm ebb (German: “Sturmebbe”), sea level blowout [4], 
or negative storm surge [5]. For this study, we will use the term extreme low water (hereafter 
”ELW”) to address tidal low water levels (LWs) that are additionally influenced by offshore 
winds and hence significantly below mean low water (mLW). This is to distinguish from the 
solely wind-driven part of the water level reduction apart from tidal level, and which we 
call “negative storm surge” (NSS) in this manuscript. 
Besides the term also the definition of what is considered an NSS or an ELW varies 
in the literature. In a number of studies, a threshold-based approach is used where every 
Academic Editor: Alfredo Rocha 
Received: 13 June 2022 
Accepted: 21 September 2022 
Published: 7 October 2077 
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Atmosphere 2022. 13. 1634. https: / /doi.org /10.3390 /atmos131016234 
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