Sea level rise a different kind of dilemma for Hamburg, Germany. The city that was traumatized by the 1962 flood is now building infrastructures higher and higher. First dikes and now city plinths, how high would the Germans have to build to stay dry?
Earth.Org has mapped the high-level flood potential the low-lying city could suffer by 2100 with current sea level rise projections.
Dikes and seawalls surrounding Hamburg have been elevated twice after two flooding episodes. The first was in 1962 when the North Sea flood caused the Elbe river to swell and occupy ⅙ of Hamburg’s area. Then, in 2017, Hamburg’s famous fish market was flooded as storm Sabine caused the Elbe to rise by 2.76 meters. In reaction, the dikes have been raised from 5 meters to a varying height of 7.5 meters to 9.25 meters since they were first built.
Uniquely, apart from constructing shields, architects from Hamburg immersed themselves into an ambitious project called the Hafencity. Built on a small island and formally inaugurated in 2008, this neighborhood is an urban regeneration project, featuring many new hotels, shops and residential areas. A sophisticated flood control system was incorporated because dikes would cut off the view and be extremely expensive. Instead, all roads and public spaces were elevated on sand terraces over 7.5 meters high.
All shore-adjacent buildings must be water-proofed and provide access to the elevated areas in case of flooding. The HafenCity is considered the largest urban redevelopment project in Europe, at least in terms of landmass.
Meanwhile, the rest of Hamburg is counting on as a $592-million dike renovation project over the next 30 years to hold back alarming rates of sea level rises. Earth.Org has modeled the possible consequences of high tides in Hamburg by the end of the century.
Global mean sea level is projected to rise by 2m at the end of this century. However, in order to determine local sea level rise (SLR), one has to take into account local coastal flood levels which could be 2.8m above Mean Higher-High Water (MHHW) at extreme forecasts. These local levels bring variability to the projected SLR from 1m to 6.5m (eg. Rio vs Kolkata).
The SLR scenarios used in this study are based on the forecasts from Climate Central – Coastal Risk Screening Tool with the following parameters:
- Sea level Projection Source
- Coastal Flood Level
- Pollution Scenario
Sea level Projection Source
From two highly cited journals by Kopp et al., estimating SLR mainly due to ocean thermal expansion and ice melt. The mid-range scenario projected 0.5-1.2m of SLR based on different representative concentration pathways (RCP) defined by the IPCC. While the pessimistic scenario added more mechanisms of ice-sheet melting, estimating SLR at 1m-2.5m in 2100, with a projection of 10m SLR at 2300.
More frequent coastal flooding is a direct impact of sea-level rise. Based on the Global tides and surge reanalysis by Muis et al., (2016), it is estimated that the extreme coastal water level could be from 0.2 – 2.8m over the mean level. While in extreme cases like China and the Netherlands it could experience 5-10m of extreme sea levels. Here, the coastal local flood level is added on top of the projected SLR.
Allows choosing the RCP, the greenhouse gas concentration trajectory defined by the IPCC. The mild level is based on RCP4.5, of 2°C temperature rise; while the Extreme level is based on RCP 8.5, of 4°C temperature rise.
Applies to the baseline SLR, defined in the “Sea level projection” section, upon which we add flooding. “Mild” refers to the mid-range scenario of 0.5-1.2m, and “extreme” to the pessimistic scenario of 1-2.5m. We used the high-end value of each scenario (mild = 1m; extreme = 2.5m).
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This article was written by Eva Angela Seputra and Owen Mulhern.
Kulp, Scott A., and Benjamin H. Strauss. “New elevation data triple estimates of global vulnerability to sea-level rise and coastal flooding.” Nature communications 10.1 (2019): 1-12.
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