Financial feasibility of large-scale adaptation strategies for future SLR in northern Europe: NEED vs dike reinforcement

Abstract

The effects of climate change are felt all around the world. An increased sea level goes hand in hand with an increased risk of flooding. To combat this, the coastlines must be reinforced to withstand future sea levels. However, repeatedly reinforcing coastlines to keep up with the sea level rise (SLR) could prove extremely costly. An alternative approach would be to shorten the coastline, as the Netherlands did with the Afsluitdijk to enclose the IJsselmeer. Looking at Europe, Groeskamp and Kjellsson (2020) proposed the construction of the Northern European Enclosure Dam (NEED) — a dam that would disconnect the North and Baltic Seas from the Atlantic Ocean. In this way, it would protect fifteen northern European countries against the accelerated global mean SLR (GMSLR), as it simultaneously shortens the coastline that requires reinforcement. This thesis aims to determine whether the NEED (Adaptation Strategy 2) would be a financially favourable adaptation strategy over raising the coastal defences on a country-by-country basis (Adaptation Strategy 1) around the North Sea to combat future GMSLR, and if so, at which GMSLR.

Through the use of the GLOFRIS model framework it was possible to estimate that by 2080 a total of 15,000 km2 would be inundated, affecting 9.5 million people and resulting in damages up to 1 trillion € for all fifteen countries combined. Reinforcing the regional flood protections (Adaptation Strategy 1) is estimated to have a total cost range of 245 to 335 billion € for a 1-metre GMSLR with an increase in costs between 170 and 235 billion € per metre GMSLR. The construction of the NEED (Adaptation Strategy 2), using an earth-fill dam design with 1:6 slopes on either sides, is estimated to be just under 1.1 trillion €, with an increase in costs of 11 billion € per metre GMSLR.

It was found that the NEED flood protection adaptation strategy will eventually become more financially favourable over the regional strategy. Estimated to be more cost-effective beyond 5.15 metres GMSLR, which is associates with construction costs of roughly 1.15 trillion €. This GMSLR for scenario SSP5-RCP8.5 is expected to occur between 2280 and 2660, approximately. However, as the total costs are greatly contingent upon the core material, modifying slope angles of the NEED design will lead to a significant reduction in volume and, hence, costs. For the alternative designs with a 1:4 and 1:5 slope, the total costs are reduced by 17% and 34%, respectively. For these designs, the NEED will already become favourable at 3.35 and 4.25 metres GMSLR, respectively.

Several cost distributions have been created based on the four aspects that have been investigated, namely (i) coastline reinforcement length, (ii) size of inundated area, (iii) population exposed and (iv) economic damages caused by flooding. Together with the extrapolated regional costs per country, it is possible to determine which distribution is the most and least financially favourable for each country and whether contributing to the NEED is even favourable at all from the perspective of each country.

This research scrutinised the costs, effects and consequences of the most extreme scenario that generated the greatest exposure indicator values (i.e. SSP5-RCP8.5 combined with a return period of 1000 years). Through this
assessment, it was possible to estimate the costs associated with both adaptation strategies, and furthermore, to determine at which GMSLR one strategy surpasses the other in financial attractiveness and when this GMSLR can be expected. However, it should be noted that recent studies have shown that, in reality, the most extreme scenario might, unfortunately, turn out to be even more extreme than the most extreme scenario assumed in this thesis. And as the consequences strongly dependent on how climate change will unfold in the future, the costs to combat and the timing of such GMSLR occuring will differ.

The results retrieved from this research provide insight into when the NEED flood protection adaptation strategy will become a better alternative to regional flood protection reinforcement. However, it should be borne in mind that it is not a matter of ‘either-or’, but rather ‘both-and’, as regional dike reinforcement cannot entirely be omitted when deciding to construct the NEED. Instead, a balance must be found in the extent to which regional dike reinforcement is required to protect the countries while the NEED is under construction. So there are plenty of uncertainties and questions that require additional research to fully comprehend all the effects of this massive operation and making it feasible.