Atmosphere 2022, 13, 1634 
14 of 21 
beyond this threshold. Hence, we consider such extreme effective winds a reasonable 
proxy for the risk of ELWs, not taking into account any actual tide phases of course. The 
result is very much in line with what has been shown for the SE LWT as well as the gale 
strength already. SMHI-LENS shows a systematic shift towards less frequent situations with 
extreme effective winds under climate change. The stronger the climate change scenario, 
the lower the frequency of extreme effective winds, SSP2-4.5, SSP3-7.0, and SSP5-8.5 being 
significantly different from the historical experiment regarding the median frequency. 
3.5.2. Influence of Future SLR on Negative Storm Tide Water Levels 
The focus of this study lies on the meteorological conditions associated with ELW 
However, SLR will become a non-negligible factor in this respect under continued global 
warming. Therefore, we include a sensitivity study based on the ELW event in March 2018 
(marked by a star in Figure 3) and hydrodynamic modelling of different SLR scenarios for 
this particular event. The results are shown in Figure 13. It indicates, to which amount the 
lowest LW would rise at Cuxhaven and St. Pauli solely due to SLR. This is displayed as the 
relative increase, i.e., the rise of ELW due to SLR, scaled by SLR. That means, e.g., for the 
leftmost data point in Figure 13, that the 2018 event is subject to an SLR of 0.1 m would 
yield an approx. 0.09 m higher water level in St. Pauli. The relative increase is slightly 
higher in Cuxhaven than in St. Pauli. At both locations and for all simulated scenarios the 
increase lies between 88 and 98% of SLR. 
'00 
» 
98 
96 
40 
en EU NEER UNSERER DEEERET RUE 
94 
92 
90 
88 
a 
Oo Cuxhaven 
x StPauli 
86 
X 
& 
84 
n 2 
0.4 
36 
DS 
SIRinm 
Figure 13. Simulation results: Increase of the lowest ELW in March 2018 relative to several sea level 
rise scenarios between 10 and 110 cm at Cuxhaven and St. Pauli. 
4. Discussion 
4.1. Development of Past LWs in the Elbe Estuary 
Observations of LWs in the Elbe estuary since 1963 show a strongly decreasing trend 
for the median LW levels at St. Pauli and a slightly increasing trend for Cuxhaven. The 
minimum LW of each year, which is most likely strongly influenced by wind, shows 
a related decreasing and increasing trend for the two stations. The increase of LWs at 
Cuxhaven is very likely to be mainly caused by past sea level rise. According to [14] 
global mean SLR between 1971 and 2018 was in a likely range of 1.55 and 3.12 mm/a. For 
Cuxhaven, a regional mean SLR of 3.6 + 0.8 mm/a between 1971 and 2008 was calculated 
by [57]. At St. Pauli the observed LW is still influenced by varying discharge into the 
estuary. The decreasing trend of LWs at St. Pauli can be caused by the anthropogenic 
changes in the estuary geometry [58], as well as morphological changes and low discharge