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at the gauge Neu Darchau [29]. A constant salinity of 33 PSU at the seaward boundary 
and 0.4 PSU for the upstream inflow is assumed. The water level at the seaward boundary 
of the model is derived from the Dutch Continental Shelf Model DCSMv6FM, which is a 
further development of DCSMv6 [54,55]. Five SLR scenarios of 10, 30, 50, 80 and 110 cm 
are simulated by adding the respective SLR at the open seaward boundary of the German 
Bight model. These scenarios approx. cover the range of SLR projections given by the 
IPCC ([14-16]). 
A comparison of simulation results and measurements of water level during the 
ELWSs 2018 at Cuxhaven, St. Pauli and other gauges in the Elbe estuary is displayed in 
Figure A2 in the Appendix A: The comparison shows that the tidal cycle is well reproduced 
by the model with respect to height and phase. The lowest LW is slightly lower in the 
simulation compared to measurement data in the mouth of the estuary and slightly higher 
further upstream. These differences could be caused due to the resolution of the model 
and the forcing data as well as the parametrization of certain processes. As [56] use a very 
similar model set up, additional information about the model and its performance can be 
found there. Rasquin et al. [56] demonstrate the importance of a high model resolution of 
coastal topography in hydrodynamic numerical simulations regarding the changes of tidal 
dynamics due to SLR scenarios. The mentioned model similarity implies that our applied 
model resolution is sufficient to simulate these scenarios. 
3. Results 
3.1. Past Development of Low Water Levels 
The development of LW in the past is displayed for the two stations Cuxhaven und St. 
Pauli. Cuxhaven is located in the mouth of the estuary, while St. Pauli is located further 
upstream close to the Hamburg harbour (see Figure 1b). The data of observed LWs was 
ased to calculate and visualize the minimum and median values of each year for the period 
1950-2019 (see Figure 2). At St. Pauli, a strong decrease of median and minimum of LW 
levels can be seen over the displayed period. For the period between 1963 and 2019, the 
length of three nodal tide periods, a significant decreasing trend of —1.01 + 0.62 (p < 0.01) 
and —1.45 + 0.18 cm/a (p < 0.001) can be detected for minimum and median at St. Pauli, 
respectively. In contrary, a weaker but significant increasing trend of +0.77 + 0.59 (p = 0.011) 
and +0.21 + 0.09 (p < 0.001) cm/a for minimum and median is detected at Cuxhaven (see 
Figure 2) for this period. Possible reasons for this observed development are discussed 
in Section 4.1. 
-50 
100 
450 — 
minimum Cuxhaven ® median Cuxhaven 
minimum St.Pauli-‘---------&--median St.Payli- 
w 
J 
; 200 + 
_-250 + 
3 
= _300 — 
-350 
a. 
-400 
T : ; 1 . . ; . 17 T- 1 1} 
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 
Var 
Figure 2. Minimum and median of tidal low water (LW) observations for each year between 1950 
and 2019 at Cuxhaven (mouth of the estuary) and St. Pauli (Hamburg harbour) relative to NHN.