How uncertainty in Antarctic mass-loss impacts the coastal adaptation strategy of the Netherlands

Published: 3 January 2020

Large uncertainty arises from potential ice mass-loss from Antarctica that could rapidly increase sea level rise in the second half of this century. The implications of sea level rise may be existential for a low-lying country like the Netherlands. To deal with uncertain sea level rise, the Netherlands has adopted an adaptive pathways plan. In a paper, published last week in Environmental Research Letters, Dutch researchers assess the potential consequences of a high and accelerated sea level rise scenario for coastal adaptation in the Netherlands, focusing on coastline, flood risk and fresh water resources management.

Large uncertainty arises from potential ice mass-loss from Antarctica that could rapidly increase sea level rise in the second half of this century. The implications of sea level rise may be existential for a low-lying country like the Netherlands. To deal with uncertain sea level rise, the Netherlands has adopted an adaptive pathways plan. In a paper, published last week in Environmental Research Letters, Dutch researchers assess the potential consequences of a high and accelerated sea level rise scenario for coastal adaptation in the Netherlands, focusing on coastline, flood risk and fresh water resources management.

Low-lying coastal zones worldwide

Worldwide, decision makers in low-lying coastal zones are confronted with uncertainties about future sea-level rise. About 10% of the world’s population lives in coastal zones that are less than 10 meters above mean sea level. These low and fertile areas provide food for hundreds of millions of people, have high ecological value, form major logistic hubs, and host megacities including New York, Tokyo, Jakarta, Ho Chi Minh City, Rio de Janeiro, Manilla, Lagos, Dhaka, London, and Amsterdam-Rotterdam.

Increased uncertainty

The Netherlands has adopted an adaptive plan that allows for adaptation over time depending on how the future unfolds. With this plan, developed within the Delta Program, the Netherlands aim to be prepared for future climate and socio-economic developments. A rapid acceleration of sea level rise will, however, significantly reduce the lifetime of adaptation measures and leaving less time to adapt, not only for the Netherlands but also for other low-lying coastal zones. Even for a well-protected developed country such as the Netherlands, the projected rate of change and increased uncertainty bandwidth has large implications and may push current strategies to their limits or beyond. Sand nourishment volumes to maintain the coast would become 20 times larger than to date under rates of 60 mm/year around the end of this century, storm surge barriers will need to close at increasing frequency until closed permanently, and intensified saltwater intrusion will reduce freshwater availability, under a rising demand.

Global mean sea-level rise including accelerated mass-loss from Antarctica for RCP4.5A (blue) and RCP8.5A (red) based on Le Bars et al. (2017) and the potential consequences for coastal adaptation. The coloured horizontal bars present an adaptation pathway existing of a sequence of measures for 0.5 m sea-level rise (from yellow to orange to red) and the functional lifetime of these adaptation measures in the event of an accelerating sea-level rise according to the median value for RCP8.5A or the 95th percentile for RCP4.5A. The lower panel shows a lead time of ~30 years for planning and implementation, and required timing of signals and decision. An alternative pathway could start with the ‘yellow’ measure and switch directly to red (dashed lines).

No-regret measures

Until 2050 the present strategy of the Netherlands is adequate and there is enough time to adapt. The results of the study show that after 2050 accelerated sea level rise may push the present strategy based on incremental no-regret measures to its limits. The uncertain but potentially rapid sea level rise has the potential to become a true gamechanger, as either incremental adaptation at an incredible pace or transformative decisions to high magnitudes of sea level rise may become necessary. This asks for intensified research into the processes that determine sea level rise, and adequate monitoring and detecting early warning signals for rapid sea level rise. In addition, exploration of no-regret measures becomes relevant, like reservations for future water storage, expanding flood protection works and future sand extraction for coastal maintenance.

Marjolijn Haasnoot, researcher Deltares and lead author: “It is not a matter of whether sea level rise will rise to certain levels, but when this will occur. This may help to overcome decision paralysis due to uncertainty. The Netherlands still has enough time to take measures, bearing in mind that there is a delay of about 20 to 30 years between making a plan and the implementation of it”.

Dewi Le Bars, researcher at KNMI: “Our understanding of how the ice sheets will respond to global warming is still far from complete but could potentially result in high levels of sea level rise by the end of this century and beyond. Therefore, it is important to investigate a large range of possible futures. Antarctica is the main uncertainty for The Netherlands, first because it represents a potential contribution to global sea level of 58 m and up to 20% more for the Netherlands, and second because the ice there is in contact with the ocean water which contains enough heat to melt the whole ice sheet.”

 


Paper: 
“Adaptation to Uncertain Sea-Level Rise; How Uncertainty in Antarctic Mass-Loss Impacts the Coastal Adaptation Strategy of the Netherlands”
published in: Environmental Research Letters, 31 December 2019

Authors:
M. Haasnoot (Deltares / Utrecht University), J. Kwadijk (Deltares / University of Twente), J. van Alphen (Staff Deltacommissioner), D. Le Bars (KNMI), B. van den Hurk (Deltares / Institute for Environmental Studies Amsterdam), F. Diermanse (Deltares), A. van der Spek (Deltares), G. Oude Essink (Deltares / University of Utrecht), J. Delsman (Deltares) and M. Mens (Deltares)