Protection Against Sea Level Rise and Storm Surge Prevents Severe Eco-nomic Losses: A Case Study in Copen-hagen

Climate change impacts in coastal cities are expected to represent a major challenge this century, with millions of exposed people and thousands of billions of USD of exposed assets at the global scale. As a low-lying city with a significant number of people and amount of property lying close to the water level, Copenhagen is potentially vulnerable to the effects of sea level rise. In their study, Hallegatte et al (2011) illustrate a methodology to estimate economic impacts of climate change at a city scale, taking the example of sea level rise and storm surge risks in Copenhagen. The authors’ approach is a simplified catastrophe risk assessment<!–[if supportFields]> XE “risk assessment” <![endif]–><!–[if supportFields]><![endif]–>, to calculate the direct costs of storm surges under scenarios of sea level rise, coupled to an economic input–output model. The output is a risk assessment of the direct and indirect economic impacts of storm surge under climate change including production and job losses. For Copenhagen, it is found that in absence of adaptation, sea level rise would significantly increase flood risks. Results call for the introduction of adaptation in long-term urban<!–[if supportFields]> XE “urban” <![endif]–><!–[if supportFields]><![endif]–> planning, as one part of a comprehensive strategy to manage the implications of climate change in the city. —Michelle Schulte
Hallegatte, S., Ranger, N<!–[if supportFields]>XE “nitrogen, N”<![endif]–><!–[if supportFields]><![endif]–><!–[if supportFields]> XE “nitrogen” <![endif]–><!–[if supportFields]><![endif]–>., Mestre, O., Dumas, P, Morlot, J.C., Herweijer, C., Wood, R.M. 2011. Assessing climate change impacts, sea level rise and storm surge risk in port cities: A case study on Copenhagen. Climate Change 104, 113–137.

Due to local factors such as uplift and changes in ocean circulation, the water level in Copenhagen has risen at a rate of 4 cm a year while globally, the sea level has risen17 cm over the century. In terms of regional changes, the IPCC<!–[if supportFields]> XE “Intergovernmental Panel on Climate Change (IPCC)”<![endif]–><!–[if supportFields]><![endif]–> found that sea level rise could be greater than the global average around northern Europe<!–[if supportFields]> XE “Europe” <![endif]–><!–[if supportFields]><![endif]–>, reaching up to 38–79 cm around Denmark. Because of this large uncertainty of sea level rise, several possible amplitudes of SLR<!–[if supportFields]>XE “sea-level rise (SLR)”<![endif]–><!–[if supportFields]><![endif]–> are considered, from 0 to 125 cm, and results are presented for all the cases. The authors analyzed the impact of climate change through a series of steps: (1) a statistical analysis of past storm surges in Copenhagen; (2) a geographical-information analysis of the population and asset exposure in the city, for various sea levels and storm surge characteristics; (3) an assessment of direct economic losses in case of storm surge; (4) an assessment of the corresponding indirect losses—in the form of production and job losses, reconstruction duration etc.—using an adaptive regional input–output model (ARIO); and (5) a risk analysis of the effectiveness of coastal flood protections, including risk changes due to climate change and sea level rise.
Hallegatte et al. found that in the absence of protection, potential losses would increase over time. The authors analyzed the total, direct losses of public and private (insured) land, defining direct losses as the repair and replacement cost of damaged buildings and equipment due to flooding. With 25 cm of mean sea level rise, total losses caused by a future 100-year event would rise from €3 billion to €4 billion. When this storm was coupled with a 50 cm sea level (or a total SLR<!–[if supportFields]>XE “sea-level rise (SLR)”<![endif]–><!–[if supportFields]><![endif]–> of 2 m), the damages increased by 55% to roughly €5 billion, and to €8 billion with 100 cm sea level. Thus, without protection, sea level rise increases the risk of flooding significantly.
Direct losses caused by an event are usually significantly lower than the exposure to this event. There is a complex link between exposure to high sea level and the destruction and losses caused by such episodes. The total cost of flooding in Copenhagen is equal to the sum of direct and indirect costs. The indirect cost is the reduction in production of goods and services across the economy due to the disaster. The authors analyzed the impact of a 2 m increase in sea level above present-day values on 8 sectors of value added (VA). In the early period following a storm surge, the losses and gains in VA are estimated to roughly balance each other due to reconstruction efforts. However, a total of 7,500 jobs are lost in the 3 months after the disaster and 500 jobs are lost 1 year after the shock. The sectors that are most impacted include wholesale and retail trade, finance and business activities, and transportation. However, the authors argue that adaptation measures have to focus on direct loss reduction (using dikes or reinforced buildings) as direct losses are much more vast than indirect losses.
Copenhagen is currently easy to protect against storm surges, but needs additional protection against rising sea levels. While annual mean losses can reach several billions of Euros with protection of less than 1 m, they decrease very rapidly with protection height. Economic losses decrease to less than €100,000 per year for 180 cm of protection, and null for protection higher than 202 cm. Therefore, the authors estimated that construction cost of coastal flood protection of 2 or 3 m to be a few hundred million Euros for the city. Hallegatte et al. assert that despite 202 cm of protection, a 25 cm SLR<!–[if supportFields]> XE “sea-level rise (SLR)” <![endif]–><!–[if supportFields]><![endif]–> causes €1 million a year in damages while a 100 cm SLR causes €4.2 billion per year. On the other hand, with 300 cm protection, damages only occur if SLR are >1 m. In addition, the timescale of the increases in losses cannot be determined, because of uncertainty in future SLR. In the most optimistic scenarios, sea level rise should not exceed 25 cm by 2100 while the most pessimistic studies show that SLR could exceed 1 m by 2100.
Copenhagen is very well protected against storm surges and coastal flooding due to its high standards of defense. First, in the city center and the harbor, quays are at more than 2 m above current sea level. Considering that the authors estimate the maximum possible storm surge at 2 m, this protection level suggests that this part of the city is not at risk. In locations that are at-risk, protection is present in the form of dikes. In addition, even a large SLR<!–[if supportFields]> XE “sea-level rise (SLR)” <![endif]–><!–[if supportFields]><![endif]–> could be managed by the current protection system. Only a few areas could be affected by storm surges with the current sea level and with higher sea levels. In these areas, protection will have to be upgraded to prevent coastal flood risk from increasing rapidly across the ranges of SLR considered in this study.

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