By 2100, almost 5% of the world’s population could be affected by flooding each year as a result of sea-level rise, unless we boost coastal protection or mitigate climate change. That’s according to researchers in Germany, the UK, the Netherlands, Austria and Belgium who performed the first study to take into account different scenarios for population, climate, socioeconomic development, regional patterns of sea-level rise, adaptation strategies and topography.
“There is concern that increasing storm-surge flooding and associated adaptation costs is one of the most costliest aspects of climate change,” Jochen Hinkel of Global Climate Forum, Germany, told environmentalresearchweb. “Yet there was no global, comprehensive study on this subject.”
Flooding associated with global mean sea-level rise of 25–123 cm – an amount feasible by the end of the century – could cause damages worth up to 9.3% of global gross domestic product, Hinkel and colleagues found. Dikes to protect coasts would be far cheaper than the damages, but would still cost between $12 bn and $71 bn each year to build and maintain by 2100.
“Our results emphasize the central role of long-term coastal adaptation strategies,” writes the team in PNAS. “These should also take into account that protecting large parts of the developed coast increases the risk of catastrophic consequences in the case of defence failure.”
The world’s infrastructure and population is in many cases distributed along the coast. According to an earlier study, around one-tenth of the global population – roughly 634 million people – lives within 10 m of sea level.
“If we ignore this problem then damages of future storm surges will be dramatic,” said Hinkel. “If, however, we adapt by e.g. enhancing coastal protection, impacts can be much reduced.”
To come up with the results, Hinkel and colleagues used four climate models from the Coupled Model Intercomparison Project Phase 5, along with three scenarios for melt of ice sheets and glaciers, three pathways for greenhouse emissions, and five scenarios for population and gross domestic product. At this stage, they did not allow for the expected continuing coastward migration and urbanization, sea-level rise from groundwater depletion for human use, or the effects of any changes in storminess or cyclone intensity.
Flood damages are much more sensitive to coastal protection strategy than to climate or socioeconomic scenarios, the researchers discovered. They considered two protection approaches – constant protection, which maintains dikes at the same height so that flood risk increases over time as sea-level rises, or enhanced protection – building dikes higher as sea level and socioeconomic development rise, and the value and density of assets needing protection goes up.
But other approaches are available. Hinkel says we need to promote mixed responses to sea-level rise including: limiting emissions to curb sea-level rise and so restrict the overall risks and costs; protecting densely populated regions with hard protection like dikes or soft protection such as dunes, mangrove forests or shore nourishment; steering future development away from the coast; supporting developing countries and small island states in meeting the costs of adaptation; and, in the longer term, exploring where we could retreat from the coastline.
Now the team plans to examine some of these more diverse adaptation options, including ecosystem-based adaptation, set-back zones and building codes, and will consider “at which location what kind of strategy is robust”.
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