A new study warns that land subsidence is making the danger of rising sea levels even greater. Earth's sinking cities are slipping toward sea level at an alarming rate, and subsidence more than doubles the rate of sea level rise for some areas of the coastline.
Rising sea levels are already putting millions at risk of flooding – but a new study warns that land subsidence is making the danger even greater.
Earth's sinking cities are slipping toward sea level at an alarming rate, experts from the Technical University of Munich have warned. In a new study, scientists found that subsidence more than doubles the rate of sea level rise for some areas of the coastline. To make matters worse, researchers say that this affects the largest and most densely populated cities more than anywhere else.
Between rising seas and sinking land, heavily urbanised areas of coast experience a relative sea level increase of about six millimetres per year on average. That is three times more than the global average for relative sea level rise, which stands at 2.1 millimetres per year. Likewise, land subsidence roughly doubles the absolute sea–level rise of 3.15 millimetres per year, which measures the actual increase in volume and height of the ocean.
Lead researcher Dr Julius Oelsmann, of Technical University of Munich, says that this can 'significantly amplify the effects of climate–driven sea–level rise'. Scientists have found that land subsidence is doubling the rate at which the water level rises in some of the world's biggest cities, putting millions at risk of flooding. Jakarta is the world's fastest–sinking city, subsiding at a rate of 13.7 millimetres per year. This puts the megacity's 42 million residents in extreme danger of flooding.
As the climate gets hotter, melting glaciers and the expansion of warming water are gradually raising the level of the world's oceans. However, Dr Oelsmann and his co–authors warn that the surface of the sea only tells half the story.
'If we want to understand sea–level rise along coastlines and respond effectively, we must not only observe the ocean but also the land itself,' Dr Oelsmann says. This is because a mixture of human activity and natural forces is combining to sink some of the world's biggest cities into the ocean. The biggest factors driving this subsidence are excessive groundwater and oil extraction, which remove underground resources that previously stabilised the surface.
Dr Oelsmann points out that the 'sheer weight of cities' is also driving urban areas below sea level. As cities grow larger and taller, heavier buildings are constructed, which compacts the ground beneath and slowly sinks the city relative to its surroundings. Combined with climate–change–driven sea level increase, urban areas are seeing the waterline rise a lot faster than the rest of the world.
In the UK, the US, and Europe, areas of the coastline are sinking into the sea due to land subsidence. This is leading to a significantly faster rate of relative sea level increase. Prominent subsidence hot spots include: Countries where relative sea levels are rising the fastest include Thailand, Bangladesh, Nigeria, Egypt, China, and Indonesia, where the ocean is getting seven to 10 millimetres higher each year.
The US, the Netherlands, and Italy also experience exceptionally rapid increases, with relative sea levels rising by around four to five millimetres per year. Due to the strong influence of city size, many countries also featured intense 'hot spots' of subsidence. The 42 million residents of Jakarta, Indonesia, the world's most populous city, are in particular peril as the megacity slips towards the ocean at a rate of 13.7 millimetres per year.
This is closely followed by Tianjin, China, home to 13.8 million people, which is seeing 13.5 millimetres of subsidence per year. Similarly, Bangkok, Lagos, and Alexandria are all experiencing well above average rates of subsidence with 8.5, 6.7, and four millimetres per year, respectively. Even within cities, the different rates of subsidence meant that one neighbourhood might be falling towards the ocean while others rise out of it.
In Jakarta, for example, some parts of the city are sinking at a staggering 42 millimetres per year, while other regions actually see uplift. Densely populated urban coastal regions are experiencing around six millimetres of relative sea level increase per year (red regions). This means that millions of people in some of the world's biggest cities are being put at risk of severe flooding.
Even if their homes don't fall completely below sea level, every millimetre of relative sea level increase creates a bigger risk that storms or extreme weather will lead to severe floods. This is especially concerning for Jakarta, where about 40 per cent of the city is below sea level. Studies estimate that nearly half of the city could be inundated and uninhabitable by 2050 if sea levels continue to rise at the current rate
Rising Sea Levels Land Subsidence Climate-Driven Sea Level Rise Earth's Sinking Cities Prominent Subsidence Hot Spots Countries With Rising Sea Levels Jakarta Indonesia Tianjin China Bangkok Lagos And Alexandria
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