Atmosphere 2022, 13, 1634 
16 of 21 
Elbe estuary revealed a similarly strong influence of SLR on the water levels along the 
estuary including the station St. Pauli, as we observed for the ELW 2018. NSS and resulting 
ELWSs occur as a result of the interaction between astronomical tide and meteorological 
conditions and are therefore individual in their characteristics. Nevertheless, it can be 
assumed, that the possible influence of future SLR on other ELW events in the Elbe estuary 
is in the same order of magnitude, as the essential interactions of involved driving forces 
remain the same. It should be noted, that all simulation results were derived with reference 
topography in the Elbe estuary from the year 2019. The effect of possible future changes 
of estuary topography are therefore not included in the displayed results. As discussed 
for the development of LW observations in the Elbe estuary, topographic changes strongly 
influenced LWs at St. Pauli in the past. It can be assumed, that tidal flats in the Wadden 
Sea will grow to a certain amount with sea level rise, as they did in the past [60], because 
coastal topography and tidal dynamics strive towards a morphodynamic equilibrium [61]. 
However, future morphologic changes in the context of climate change and accelerated SLR, 
as well as anthropogenic measures in the Elbe estuary are difficult to estimate. Therefore, 
reliable predictions of future topography in the Elbe estuary are not available based on 
‚oday’s knowledge and further investigation in this regard is needed. 
5. Conclusions and Outlook 
This article investigated the impact of large-scale meteorological conditions as well as 
changing sea levels on ELWSs in the Elbe estuary. 
Different parameters were considered in the 24 h preceding an ELW at the gauge in 
Cuxhaven in order to analyse which atmospheric conditions (weather type, storminess 
and effective wind) prevail before such an extreme event. The investigations show that the 
SE weather type is represented 8 times more frequently before an ELW than it would be 
expected climatologically. Effective wind speeds (wind direction of 142°) with more than 
10 m/s occur 17 times more frequently than expected from climatology. 
Furthermore, possible future changes in these parameters were analysed using a 
single-model large ensemble of the GCM simulations with 4 different future scenarios. All 
three previously considered parameters show a significant decrease in the frequency of 
conditions favourable for ELWs for the far future (2071-2100), especially in the highest 
emission scenario SSP5-8.5. 
In addition to changing atmospheric conditions, future ELWs in the Elbe estuary will 
be influenced by SLR: Projections for future SLR are varying for the different SSP-scenarios 
within a range of 51 and 85 cm for the median at Cuxhaven for the year 2100 relative to 
the reference period 1995-2014 [14-16]. Our simulation results indicate, how different SLR 
scenarios would increase the lowest ELW in March 2018. At the locations Cuxhaven and St. 
Pauli the increase lies between 88 and 98% of the simulated SLR scenarios of 10, 30, 50, 80 
and 110 cm. It can be assumed, that the possible influence of future SLR on ELW events in 
the Elbe estuary is in the same order of magnitude as determined for the ELW 2018. SLR 
will therefore lead to less extreme and fewer ELWs in the future. 
Therefore, our study suggests that both SLR and meteorological conditions in a warmer 
future climate will be less favourable for the occurrence of ELWs in the Elbe estuary, but— 
ıf they occur—can be associated with significant negative effects on shipping transport 
towards the Port of Hamburg as well as certain waterfront structures. 
These results for potential future changes should and will be reviewed based on 
the extended analysis of a multi-model ensemble in order to account for the existing 
model uncertainty. Nevertheless, the prospect of a potential decrease in ELWs due to 
both—less favourable meteorological conditions and SLR—raises the question whether 
(positive) storm tides in contrast might increase in strength or frequency in the future. 
Even though this topic is much better covered by existing studies, further investigations 
in this respect based on the most recent generation of climate models and future 
scenarios are desired.