Atlantis may be a fictitious island lost to the sea, but for hundreds of coastal cities around the world Plato’s story may prove to be a prophecy.
“There are 570 coastal cities with a total urban population of over 800 million, both rich and poor, with varying degrees of infrastructure preparedness and in climates hot and cold, that are vulnerable to a climate change-induced sea level rise of just 0.5 meters by 2050
Research from the Intergovernmental Panel on Climate Change suggests a 2°C increase in global average temperature will cause global sea levels to rise between 0.35 and 0.93 meters by 2100†. Other studies suggest this could be much higher.
This magnitude of sea rise will displace people, destroy land and property, and generate billions of dollars in losses in many cities. There’s also potential harm to transport infrastructure, farmland, sanitation and drinking water, and ultimately it could cause a city to become uninhabitable.
Rapid urbanization is also exacerbating the problem together with the destruction of coastal mangroves, reefs, marshes, sand dunes and wetlands, which act as natural flood defenses.
So, what is the solution for these communities: fight the rising tide or abandon their city to become an Atlantis of tomorrow?
“There’s no simple solution as the impact of rising sea levels will manifest itself in different ways at a regional level,” says Amar Rahman, Global Risk Engineering Practice Leader for natural hazards resilience at Zurich Insurance Group (Zurich).
“There’s a misconception that sea levels will rise uniformly over the planet, but it will differ regionally, dependent on a number of factors. Cities exposed to hurricanes or typhoons could potentially have their storm surge risk amplified, while the extent of coastal erosion will vary regionally as it is dependent on local wave dynamics,” explains Rahman.
Michael Szönyi, Head of Zurich’s Flood Resilience Program, says these coastal cities must first control the creation of new risk. “This means adopting policies that prevent new developments or an increase in population density arising in areas that are going to be most affected by sea level rise,” he explains.
For existing flood risks, many cities are investing in solutions to keep seas at bay, including sea walls, storm surge barriers, water pumps and overflow chambers.
Other cities have switched their attention to environmental approaches. This may involve land recovery and the restoration of mangroves and wetlands to help cities cope with floodwater inundation.
The Netherlands is proving both strategies work. Almost a third of the country is below sea level, but it is protected by a 3,700km (2,300 mile) network of dikes, dams and seawalls, including the famous Maeslant Barrier that shields the delta city of Rotterdam.
In the past two decades, the Dutch have complemented this hard infrastructure with water management strategies. This includes spatial planning that uses city parks and public spaces as emergency reservoirs for floodwaters, and a new concept called ‘Room for the River’ introduced over a decade ago. It allows rivers to expand to cope with extra water by lowering floodplains, widening rivers and building side channels.
But in Jakarta, one of the 570 coastal cities highlighted at risk, there lies an even bigger issue: the megacity is literally sinking as the sea around it rises.
Jakarta is not the only city sinking, but its issues are particularly acute, with parts in the north sinking by up to 25 cm a year. Today, about 40% of the city sits below sea level.
11 sinking cities that could disappear by 2100‡
One of the key reasons for this severe land subsidence is excessive groundwater extraction. Jakarta’s system of water pipes reaches only one-third of residents. The rest pump water – often illegally – for drinking, washing and other purposes from aquifers deep underground as the rivers are too polluted.
“Despite the rains, groundwater is not replenished as 97% of the city is covered in impermeable asphalt and concrete. So, when groundwater is pumped out, the land above sinks as if sitting on a deflating cushion."
“Subsidence is a difficult problem to solve,” says Rahman. “At a building level it’s a disruptive and costly exercise, but how do you do it for a whole city? And it’s not just about preventing buildings from sinking, there are sewers, pipes, cables and other key infrastructure all underground. The work required would paralyze Jakarta.”
With these challenges, Indonesia’s 2017 announcement that it plans to relocate its national capital to the province of East Kalimantan, on Borneo, could be a shrewd decision.
Szönyi believes relocating cities, or parts of cities, could be a viable option. “In the past there was a long tradition of abandonment due to environmental changes, such as drought or a loss of industry. Maybe we need to revive this tradition.
“I’m not suggesting cities in a situation like Jakarta abandon the whole city, but undertaking a managed retreat might be a good option for the long run. Some cities could give up coastal land that would protect people living in those areas, while providing a flood defence for the rest of the city’s population.”
But in the meantime, Jakarta’s population could find some inspiration from the Dutch.
For more than 1,000 years, the Netherlands has been fighting back water and today has some of the world’s most sophisticated sea defences. But this century, with its ‘Room for the River’ and other water management strategies, it has learned to live with water.
Not only do cities like Jakarta need to learn to live with water, but respect and manage it too. This may include cleaning up rivers and canals, extending clean water and sanitation to all residents, and introducing measures to restrict groundwater extraction. And these cities may also have to consider the Atlantis option and abandon some city districts to the sea.
*The Future We Don’t Want technical report (February 2018): C40 Cities, Global Covenant of Mayors, Acclimatise, and the Urban Climate Change Research Network (UCCRN)
†[Global Warming of 1.5°C (2018): IPCC, Summary for Policymakers. Masson-Delmotte, V., P. Zhai, H.-O. Pörtner, D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C. Péan, R. Pidcock, S. Connors, J.B.R. Matthews, Y. Chen, X. Zhou, M.I. Gomis, E. Lonnoy, T. Maycock, M. Tignor, and T. Waterfield (eds.)].](https://www.ipcc.ch/sr15/)
‡These 11 sinking cities could disappear by 2100 (September 2019): Talia Lakritz.
Global Risks Report 2020 (pdf)