From Rotterdam to Tarakan, coastal cities must deal with rising sea levels and extreme weather threats
By Megan Darby
Sea levels are rising and so are urban populations. Increasingly volatile rainfall patterns mean flooding and drought.
Coastal cities face particular threats from climate change. So what are local authorities doing to protect people, property and ecosystems?
RTCC found three very different approaches in Australia, Indonesia and the Netherlands.
First, do no harm
More than half a million people live sprawled along 52km of shoreline in Gold Coast, Australia.
Just south of Brisbane, the city is built on no fewer than seven flood plains. A spell of exceptionally heavy rainfall could do a lot of damage.
The local government is aware of the risks and has placed restrictions on building in areas that would be flooded by the kind of storm that comes round once a century.
But with economic growth and cheaper housing political priorities, there is pressure to find space for new homes.
In the Nerang catchment, residents are protected from flooding by the Hinze Dam, which regulates the flow of water.
The height of the dam was raised in 2012, creating an extra buffer against extreme weather. Other things being equal, this should make it safe to build on lower ground than before.
The council had a decision to make: lower the flood planning level and allow 5,000 more homes to be built, or maintain existing restrictions.
Officials warned the councillors that other things were not equal. Climate change will make rainfall extremes increasingly likely and the benefits of raising Hinze Dam will have eroded by 2060.
In the long run, they argued, building these homes will be bad for the economy. This view prevailed and flood plain regulations stuck.
Save the proboscis monkey
The Indonesian city of Tarakan was once surrounded by dense mangrove forests, home to the proboscis monkey or bekantan.
An island just off the coast of Borneo, Tarakan’s population has swelled to nearly 200,000. Tropical trees have given way to shops, offices and apartments.
Meanwhile, the bekantan population across Borneo has halved in the past four decades, propelling the species onto the IUCN’s Red List of endangered animals.
Tarakan mayor Jusuf Serang Kasim decided to save at least some of the historic forest, declaring 21 hectares a conservation zone.
As well as supporting diverse ecosystems, mangroves provide a buffer against tropical storms and prevent coastal erosion. The zone has become a popular tourist attraction.
Create “sponge zones”
Some 80% of Rotterdam, the Netherlands, sits below sea level. The port city’s survival depends on an elaborate infrastructure of dykes and dams.
Keeping water at bay is nothing new to the city authorities, but climate change is ramping up the risks.
More erratic rainfall patterns mean flooded basements at one extreme and subsidence of levees – as drought dries out the ground – at the other. Water quality is declining.
With an urban population of one million in a tight space, Rotterdam is all hard surfaces. Rain runs swiftly off roofs and roads, meaning intense bursts of rainfalls can overload the city’s drainage network.
The answer is a network of “sponge zones”, or parts of the city that can retain and release water as needed.
Most ambitious of these is Benthemplein water square. A basketball court and skate park in dry weather, the sunken civic space is designed to fill up with water from surrounding rooftops when it rains. It can hold up to 1.7 million litres of water, which then drains gradually after the downpour finishes.