Zeeland, the North Sea Flood of 1953 | Photo: ANP (collection Spaarnestad), Nationaal Archief
Zeeland, the North Sea Flood of 1953 | Photo: ANP (collection Spaarnestad), Nationaal Archief
Current Dutch flood protection policy focuses on strong flood defences to limit the risks of large-scale flooding (layer 1 of our so-called multi-layered safety approach). This results in very low probabilities of flooding, but the consequences (damage and casualties) can be very large due to the low altitude of the country. Due to sea level rise and increasing river discharges, the Netherlands will need increasingly higher and wider flood defences to keep flood probabilities sufficiently low. The guiding principle of the conceptual perspectives ‘protect’ and ‘advance’ is to control or reduce the probability of flooding. ‘Re-commodate’, on the other hand, focuses on preventing damage by proactively and timely withdrawing from flood-prone areas and mitigation of the consequences of flooding by local measures to homes and businesses.
Re-commodate as a long-term possible solution
Previous research by the Sea Level Rise Knowledge Programme distinguished between two variants of re-commodate: 'pure play' and 'hybrid' [2]. In the 'pure play' strategy, flood defences would no longer be reinforced after 2050: citizens and businesses in flood-prone areas would be relocated to higher ground and, where possible, buildings and infrastructure will be adapted to mitigate the impact of flooding (layer 2 of the multi-layered safety approach). This strategy also aims for fewer casualties through improved evacuation options (layer 3 of the multi-layered safety approach). A period of 100 years is envisaged for this transition. Re-commodate on a 'pure play' basis was assessed as unrealistic in the Sea Level Rise Knowledge Programme, because this variant severely affects the earning capacity of the Randstad, the densely populated urban agglomeration which currently forms the economic heart of the Netherlands. According to the Programme this area is essential to fund the transition. Moreover, protecting the Randstad using flood defences is both technically and financially feasible. Therefore, in the 'hybrid' strategy, re-commodate only takes place from areas below sea level and flood-prone areas along the major rivers (hereinafter: the 'transition areas'), and only the Randstad will remain well-protected with strong flood defences.
We estimated the costs of several variants of the hybrid strategy [3], based on the building blocks of ‘retreat’ and the multi-layered safety approach, referred to as 'accommodate' by the IPCC in 1990. Note that in these strategies no levee reinforcements for protection are foreseen [4]. Financial and economic effects of maintaining the existing protection during the 100-year transition period were included in this evaluation. Costs have been estimated for the period 2050 to 2200, as the aftermath of the transition (beyond 2150) will continue to generate costs.
Four courses of action have been identified for the transition areas:
In line with all conceptual perspectives explored in the Sea Level Rise Knowledge Programme, a situation in 2050 in which all flood defences meet current statutory standards is taken as the reference, along with an extreme scenario in which sea levels rise by 5.15 metres between 2050 and 2200 (i.e. 5.4 metres compared to the current situation) [5].
Impact on homes, businesses and land use
A map from the 'Spatial assessment framework for a climate-adaptive built environment' [6] was used to estimate the flooded area; see Figure 1. In transition areas, around 4 million homes are estimated to be affected by flooding in 2050, of which an estimated 1.7 million (42 percent) could remain habitable by taking local measures. For 2.3 million homes (58 percent) this will not be possible. For businesses and other fixed capital assets, the same percentages have been assumed. Furthermore, frequent floods and the loss of the IJsselmeer as a freshwater basin will mean that 1.3 million hectares of agricultural land will no longer be arable.
Figure 1. Image of the flooded area used for estimating the costs of ‘re-commodate’. T100K refers to a recurrence of the depicted water depths with a frequency of once every 100,000 years. Properties that can be flooded up to a maximum of 1 metre are considered to be habitable. The Randstad area (highlighted in yellow) will remain protected in all cases.
Costs and social impacts
In line with the concept of costs in social cost-benefit analyses, ‘costs’ in this study refer to the monetized negative effects on social welfare associated with the ‘re-commodate’ perspective. Costs evaluated in this study involved:
These costs have been estimated based on reports on the value of the fixed capital stock (Statistics Netherlands, CBS), the systemic analysis carried out by the Sea Level Rise Knowledge Programme, which determined the costs of flood defences in the event of extreme sea level rise [7], and studies as part of the Delta Programme Safety [8]. Impacts on the labour market, housing market and financial market have been qualitatively or semi-qualitatively interpreted, and socio-economic and spatial distributional aspects have been addressed. Table 1 provides an overview.
Table 1. Overview of the costs of the four variants of the hybrid re-commodate strategy vs. continuing the current flood protection policy over the period 2050–2200 (price level 2025; discounted costs based on a discount rate of 2.25 percent per year [9])
Conclusions
Based on these findings, the following conclusions can be drawn.
For each variant of the hybrid re-commodate strategy, the societal costs are significantly higher than the costs of continuing the current strategy based on protection. Just the costs of gradually relocating homes, businesses and other capital assets to higher ground are 4 times greater (≈ €3,000 billion vs €800 billion) in absolute terms and 10 times greater (≈ €1,200 billion vs €140 billion) in terms of the funds needed, compared to the costs of continuing the current flood protection policy.
Choosing not to reinforce flood defences during the transition period will lead to catastrophic economic risks, due to a high probability of extreme damage from which recovery is not reasonably possible. If the transition occurs over a 100-year period and flood defences are not reinforced during this time, the transition area will face rapidly increasing flood probabilities and catastrophic effects. Large-scale floods will then occur so frequently, well before 2150, that the reconstruction of properties will be out of the question.
The multi-layered safety approach (accommodate) does not provide sufficient relief to manage these catastrophic risks. While damage to homes and businesses will decrease due to the multi-layered safety approach, a significant proportion of fixed capital assets in transition areas will still be flooded in the long term. As a result, the risks will remain catastrophic.
The other costs of re-commodate are relatively modest, but can have a negative impact on the investment climate and social inequality. Re-commodate will mean that agriculture and the supply of drinking water will no longer be possible in their current forms. There will be negative effects on the labour-, housing- and financial market and – without compensating measures – socio-economic inequality in the Netherlands will increase. These impacts will also occur in case of retreat during the transition phase. Compared to the large increase in flood risk and devaluation of real estate, these are relatively 'modest' costs. The impact on the investment climate and social inequality will be significant, but have not been quantified.
The only variant of a hybrid re-commodate strategy that is somewhat realistic, i.e. in which the risks do not become catastrophic, involves the withdrawal of homes and businesses from the transition areas, with flood defences being reinforced during the transition period (R+P100). The costs of this strategy are roughly 10 times higher compared to continuing the current flood protection policy.
A less extreme scenario for sea level rise would lead to smaller increases in flood probabilities and a slightly more favourable case for the different variants of the hybrid strategy. But even then, without strengthening flood defences, flood probabilities will eventually become very high and the consequences catastrophic. Although possible side benefits of ‘re-commodate’ for nature or other societal functions were not considered in our research, there seems to be no economic argument to opt for this drastic strategy.
Among the adaptation strategies investigated by the Sea Level Rise Knowledge Programme to prepare the Netherlands for sea level rise, are hybrid variants of 're-commodate’, which combine components of ‘retreat’ and ‘accommodate’. In re-commodate strategies, citizens and businesses are relocated from low-lying to high-lying parts of the Netherlands, or properties are adapted to make them more resilient to flooding. An estimate of the financial and economic consequences of four such variants (from 2050 onwards) shows that the social costs of all variants are significantly higher than those of continuing the current flood protection policy. If a variant is chosen in which flood defences are no longer maintained during the anticipated transition period of 100 years, this will lead to catastrophic economic risks due to the high probability of extreme, irreparable damage. From a financial-economic perspective, the only variant in which the risks do not become catastrophic is the withdrawal of all homes and businesses, with all flood defences kept reinforced during the transition period.