Tag Archives: Coastal cities

World’s coastal cities face risk from land and sea

As the tides rise ever higher, the world’s coastal cities carry on sinking. It’s a recipe for civic catastrophe.

LONDON, 15 March, 2021 − Citizens of many of the world’s coastal cities have even more to fear from rising tides. As ocean levels swell, in response to rising temperatures and melting glaciers, the land on which those cities are built is sinking.

This means that although, worldwide, oceans are now 2.6mm higher every year in response to climate change, many citizens of some of the world’s great delta cities face the risk of an average sea level rise of up to almost 10mm a year. Both the rising waters and the sinking city streets are ultimately a consequence of human actions.

Humans have not only burned fossil fuels to alter the planet’s atmosphere and raise global temperatures, they have also pumped water from the ground below the cities. They have raised massive structures on riverine sediments; they have pumped oil and gas from offshore, and they have dammed rivers to slow the flow of new sediments.

And because of such steps, some of the world’s great cities have been steadily going downhill. Tokyo in Japan has subsided by four metres in the course of the 20th century. Shanghai in China, Bangkok in Thailand, New Orleans in the US and Djakarta on the island of Java in Indonesia have all sunk by between two and three metres in the last 100 years.

Now a new study in the journal Nature Climate Change has found that 58% of the world’s coastal citizens live on soil and bedrock that is collapsing beneath their feet. Fewer than 1% are settled on terrain that is uplifting. Most are exposed to possible relative sea level rises of between 7.8mm and 9.9mm a year.

“The message to governments and local authorities is: start thinking about subsidence now”

“We wanted to look at the big picture globally, to better understand the impact of global sea level rise combined with measurements of sinking land,” said Robert Nicholls, of the University of East Anglia in the UK.

“We found that coastal populations live with sea level rise at three and four times the global average and that the impacts of sea level rise being experienced today are much larger than the global numbers being reported by the Intergovernmental Panel on Climate Change.”

So the message to governments and local authorities is: start thinking about subsidence now.

Coastal flooding has been a source of increasing alarm for a decade. Eight years ago, researchers warned that by 2050 coastal floods could be costing the world US$1 trillion a year.

Since then individual research teams have been looking at the risks from extremes of rainfall, storm surges, shifts in ocean temperatures and currents, to find that by the century’s end what had once been once-a-century events could become 10 times more frequent.

Faulty readings

And yet another group has questioned the assumptions on which sea and coastal land heights are based. Many of the estimates have been confirmed by satellite radar topography measurements, but these in turn are based on reflections from the first surface the radar signal touches. If it falls on bare farmland, it will be accurate. If the signal hits buildings or tree tops, then the measurements might be misleading: the land surface could be much lower.

Other research teams have looked at rates of melting in Greenland and the Antarctic to warn that previous forecasts could prove to have been underestimates: by the end of the century, oceans could have risen by as much as two metres in a worst case scenario. Once again, how bad things turn out will depend on what steps humans take now.

So, like all the research that has preceded it, this last study confirms that, however bad things looked before, they now look even more alarming. The point of such research, of course, is to help governments prepare for the worst. Tokyo, Shanghai and Bangkok have already slowed the extraction of groundwater. Other nations must consider other solutions.

“One of the main reasons that Jakarta, the capital city of Indonesia, is being moved to Borneo is because the city is sinking due to groundwater extraction from shallow wells,” said Professor Nicholls.

“We hope that our analysis improves the understanding of how sea level rise and subsidence are hand-in-hand for science and coastal management policy worldwide. Jakarta might be just the beginning.” − Climate News Network

As the tides rise ever higher, the world’s coastal cities carry on sinking. It’s a recipe for civic catastrophe.

LONDON, 15 March, 2021 − Citizens of many of the world’s coastal cities have even more to fear from rising tides. As ocean levels swell, in response to rising temperatures and melting glaciers, the land on which those cities are built is sinking.

This means that although, worldwide, oceans are now 2.6mm higher every year in response to climate change, many citizens of some of the world’s great delta cities face the risk of an average sea level rise of up to almost 10mm a year. Both the rising waters and the sinking city streets are ultimately a consequence of human actions.

Humans have not only burned fossil fuels to alter the planet’s atmosphere and raise global temperatures, they have also pumped water from the ground below the cities. They have raised massive structures on riverine sediments; they have pumped oil and gas from offshore, and they have dammed rivers to slow the flow of new sediments.

And because of such steps, some of the world’s great cities have been steadily going downhill. Tokyo in Japan has subsided by four metres in the course of the 20th century. Shanghai in China, Bangkok in Thailand, New Orleans in the US and Djakarta on the island of Java in Indonesia have all sunk by between two and three metres in the last 100 years.

Now a new study in the journal Nature Climate Change has found that 58% of the world’s coastal citizens live on soil and bedrock that is collapsing beneath their feet. Fewer than 1% are settled on terrain that is uplifting. Most are exposed to possible relative sea level rises of between 7.8mm and 9.9mm a year.

“The message to governments and local authorities is: start thinking about subsidence now”

“We wanted to look at the big picture globally, to better understand the impact of global sea level rise combined with measurements of sinking land,” said Robert Nicholls, of the University of East Anglia in the UK.

“We found that coastal populations live with sea level rise at three and four times the global average and that the impacts of sea level rise being experienced today are much larger than the global numbers being reported by the Intergovernmental Panel on Climate Change.”

So the message to governments and local authorities is: start thinking about subsidence now.

Coastal flooding has been a source of increasing alarm for a decade. Eight years ago, researchers warned that by 2050 coastal floods could be costing the world US$1 trillion a year.

Since then individual research teams have been looking at the risks from extremes of rainfall, storm surges, shifts in ocean temperatures and currents, to find that by the century’s end what had once been once-a-century events could become 10 times more frequent.

Faulty readings

And yet another group has questioned the assumptions on which sea and coastal land heights are based. Many of the estimates have been confirmed by satellite radar topography measurements, but these in turn are based on reflections from the first surface the radar signal touches. If it falls on bare farmland, it will be accurate. If the signal hits buildings or tree tops, then the measurements might be misleading: the land surface could be much lower.

Other research teams have looked at rates of melting in Greenland and the Antarctic to warn that previous forecasts could prove to have been underestimates: by the end of the century, oceans could have risen by as much as two metres in a worst case scenario. Once again, how bad things turn out will depend on what steps humans take now.

So, like all the research that has preceded it, this last study confirms that, however bad things looked before, they now look even more alarming. The point of such research, of course, is to help governments prepare for the worst. Tokyo, Shanghai and Bangkok have already slowed the extraction of groundwater. Other nations must consider other solutions.

“One of the main reasons that Jakarta, the capital city of Indonesia, is being moved to Borneo is because the city is sinking due to groundwater extraction from shallow wells,” said Professor Nicholls.

“We hope that our analysis improves the understanding of how sea level rise and subsidence are hand-in-hand for science and coastal management policy worldwide. Jakarta might be just the beginning.” − Climate News Network

Coastal cities face $1tn floods by 2050

EMBARGOED until 1700 GMT on Sunday 18 August In less than 40 years from now the cost to the world’s biggest coastal cities from flooding is expected to have risen to $1 trillion – 0.7% of the value of the entire world economy in 2012. LONDON, 18 August – By 2050, flood damage in the world’s coastal cities is expected to reach $1 trillion a year as sea levels rise and global warming triggers new extremes of heat, windstorm and rain. More than 40% of these prodigious costs could fall upon just four cities – New Orleans, Miami and New York in the US and Guangzhou in China. Stephane Hallegatte of the World Bank in Washington and colleagues looked at the risks of future flood losses in the 136 largest of the world’s coastal cities. Any coastal city is always at some risk – by definition it is at sea level, and often on an estuary or floodplain, and very often began as a seaport. But risks increase as the environment changes: some coastal cities are subsiding; sea levels are slowly but surely rising as the oceans warm and the glaciers melt; and for two decades researchers have repeatedly warned that what used to be “extreme” events such as once-in-a-century floods are likely to arrive considerably more often than once a century.

More at risk

But, Hallegatte and colleagues point out in Nature Climate Change, there is another factor: populations are growing, and even in the poorest nations there is greater economic development. At bottom, for any future disaster, there will be more potential victims, with more investment to lose. In 2005, average global flood losses are estimated to have reached $6 billion a year. This figure is expected to grow to $50 billion a year, and unless cities put money into better flood defences, losses could pass the $1 trillion mark. To make their calculations, the authors matched average annual losses (and in a city like New Orleans, much of it already below sea level, this is estimated at $600 million) against a city’s gross domestic product, to provide a measure of how much should be set aside to pay for such losses. Both New York and New Orleans have already undergone catastrophic flooding this century, and flood hazard can only increase. Some cities – Amsterdam in the Netherlands is a classic example – are highly exposed to flood risk, and the once-a-century flood could cost the Dutch $83 billion, but in fact Dutch sea defence standards are probably the highest in the world. Ho Chi Minh City in Vietnam and Alexandria in Egypt have less to lose, but in relative terms both are far more vulnerable. Prophecies such as these are intended to be proved wrong: the idea is that a prophet warns of horrors to come, people take steps, and as a consequence the horrors do not arrive.

Not too late

But as disaster professionals have learned again and again, governments, city authorities, investors and even citizens tend not to listen to prophecies of doom: scientists and engineers repeatedly described what could happen to New Orleans if it was hit by a powerful-enough hurricane, and in 2005, as Hurricane Katrina arrived, the levees gave way, with catastrophic results. But, the scientists warn, Miami, New York and New Orleans are especially vulnerable, because wealth is high but protection systems are poor, and governments should be prepared for disasters more devastating than any experienced today. The paper’s authors argue that with systematic preparedness and adaptation, annual flood losses in the great global cities could be cut to $63 billion a year. Engineering projects can help, but will not be enough, so civic authorities should also be thinking about disaster planning and comprehensive insurance programmes to cover future losses. Since risks are highly concentrated – any city piles millions of people and billions of dollars of investment into a relatively small area – flood reduction schemes could be highly cost-effective. – Climate News Network

EMBARGOED until 1700 GMT on Sunday 18 August In less than 40 years from now the cost to the world’s biggest coastal cities from flooding is expected to have risen to $1 trillion – 0.7% of the value of the entire world economy in 2012. LONDON, 18 August – By 2050, flood damage in the world’s coastal cities is expected to reach $1 trillion a year as sea levels rise and global warming triggers new extremes of heat, windstorm and rain. More than 40% of these prodigious costs could fall upon just four cities – New Orleans, Miami and New York in the US and Guangzhou in China. Stephane Hallegatte of the World Bank in Washington and colleagues looked at the risks of future flood losses in the 136 largest of the world’s coastal cities. Any coastal city is always at some risk – by definition it is at sea level, and often on an estuary or floodplain, and very often began as a seaport. But risks increase as the environment changes: some coastal cities are subsiding; sea levels are slowly but surely rising as the oceans warm and the glaciers melt; and for two decades researchers have repeatedly warned that what used to be “extreme” events such as once-in-a-century floods are likely to arrive considerably more often than once a century.

More at risk

But, Hallegatte and colleagues point out in Nature Climate Change, there is another factor: populations are growing, and even in the poorest nations there is greater economic development. At bottom, for any future disaster, there will be more potential victims, with more investment to lose. In 2005, average global flood losses are estimated to have reached $6 billion a year. This figure is expected to grow to $50 billion a year, and unless cities put money into better flood defences, losses could pass the $1 trillion mark. To make their calculations, the authors matched average annual losses (and in a city like New Orleans, much of it already below sea level, this is estimated at $600 million) against a city’s gross domestic product, to provide a measure of how much should be set aside to pay for such losses. Both New York and New Orleans have already undergone catastrophic flooding this century, and flood hazard can only increase. Some cities – Amsterdam in the Netherlands is a classic example – are highly exposed to flood risk, and the once-a-century flood could cost the Dutch $83 billion, but in fact Dutch sea defence standards are probably the highest in the world. Ho Chi Minh City in Vietnam and Alexandria in Egypt have less to lose, but in relative terms both are far more vulnerable. Prophecies such as these are intended to be proved wrong: the idea is that a prophet warns of horrors to come, people take steps, and as a consequence the horrors do not arrive.

Not too late

But as disaster professionals have learned again and again, governments, city authorities, investors and even citizens tend not to listen to prophecies of doom: scientists and engineers repeatedly described what could happen to New Orleans if it was hit by a powerful-enough hurricane, and in 2005, as Hurricane Katrina arrived, the levees gave way, with catastrophic results. But, the scientists warn, Miami, New York and New Orleans are especially vulnerable, because wealth is high but protection systems are poor, and governments should be prepared for disasters more devastating than any experienced today. The paper’s authors argue that with systematic preparedness and adaptation, annual flood losses in the great global cities could be cut to $63 billion a year. Engineering projects can help, but will not be enough, so civic authorities should also be thinking about disaster planning and comprehensive insurance programmes to cover future losses. Since risks are highly concentrated – any city piles millions of people and billions of dollars of investment into a relatively small area – flood reduction schemes could be highly cost-effective. – Climate News Network