Construction Week Online 4 Apr 09;
With sea levels predicted to rise by at least half a metre this century Bahrain Editor Benjamin Millington explores what it means for the longevity of the 21st century’s coastal developments.
If you type “rising sea levels” into the Google news search engine you’ll retrieve hundreds of articles from around the world each telling the same story – we are losing our coastline.
Waves are swallowing houses in Vietnam, villages are disappearing in Ghana, Australia is making plans to relocate coastal towns, sea water is lapping at windowsills in China and the Pacific Islands are losing their islands.
In light of this, the Arabian Gulf must be the only part of the world where the length of coastline and number of islands is actually increasing rather than decreasing.
The UAE, Qatar and Bahrain are all zealously reclaiming land from the sea to create island communities where residents enjoy the beach in their backyard.
Are these people climate change skeptics? Or are the islands built on sound scientific knowledge?
The key resource for information on rising sea levels is the United Nation’s Intergovernmental Panel on Climate Change (IPCC), which collates published scientific literature and produces global climate change assessments every five to six years.
Their fourth and latest assessment in 2007 predicted sea levels would rise between 18cm and 59cm this century, a worrying set of figures for any coastal development.
But John Hunter, an Australian scientist and contributor to the IPCC assessments, said more recent predictions are even worse.
“Many people have since suggested much bigger rises, Hansen, an American scientist says the upper limit could be around 5m,” he said.
“Not many people really believe that, but another recent paper suggests with good reason that we are set for a rise between 80cm and 2m this century. “That’s what I would allow for based on the very latest research.”
Hunter said the research behind all of these predictions comes from the various scientists monitoring and computer modeling the two main factors contributing to rising sea levels.
The first is the melting of land-based ice which is mainly occurring in Greenland, Antarctica and mountain glaciers. The second is the increase in sea temperature which is causing the ocean to expand and thus sea levels to rise.
But predicting the impact of these events, which themselves are caused by a long list of complex factors, is far from precise and constantly changing. This in turn makes determining just how high above sea level it is safe to build a bit of a scientific stab in the dark.
“People may be conversant with sea level rise at the time of design and construction, but if it was 10 years ago they’d be relying on some very old IPCC research – that’s what you’ve got to be careful of,” said Hunter.
And if Hunter’s predictions of a rise between 80cm and 2m are correct, it means the largest and most well known developer of land reclamation projects, Nakheel, has based its famous Dubai projects on data that is already outdated.
Shaun Lenehan, head of environment for Dubai’s largest developer of land reclamation projects Nakheel, said its trilogy of Palm shaped island projects and the World have been built to take into account a sea level rise of 60cm this century, 20cm less than Hunter’s minimum prediction.
But this is not to say that Nakheel has been reckless in its approach to determining the height of its projects; 60cm is still at the upper end of the IPCC’s current assessment and relatively conservative in comparison to other developments.
Last October, the Bahrain government released a land reclamation and dredging manual which recommended all projects in the Kingdom only factor in a 40cm rise in sea level this century.
This, they claimed, is the optimum level to prevent “over-reclaiming” and unnecessarily building islands too high. But whether its 40cm or 60cm, as the body of scientific research grows, the potential is there for larger
predictions over the coming decades and ultimately the realisation of much bigger rises in sea levels. For coastal developments built in line with yesterdays predictions it means an increased vulnerability to storm surges and one in 100 year flooding events, which are also set to dramatically increase by 2100.
“If the sea levels only rise half a metre this century, this means that in most places, what we call a 100 year storm event will be happening about four times a year,” said Hunter. “That’s a huge change. If you’re designing things for a 1-in-100-year event you’re going to finish up at the end of the century with flooding every few months.”
“And this is actually only allowing for sea level rise. We’re not sure on how the frequency and strength of meteorological surges are going to change with climate change. If the storms get worse as well then you have to make a further allowance.”
The artificial advantage
While Nakheel and other reclamation developers will inevitably face ongoing maintenance to combat rising tides over this century, their artificial islands are unlikely to be the first coastal developments to suffer major flooding.
Lenehan explains that reclaimed islands at least have the advantage of determining the height of their development to take into account factors like sea level rises, one in 100 year storms, king tides and storm surges.
He said their projects are generally at least 3m above the water level and areas exposed to the wave climate and storm surges are built higher depending on their vulnerability.
This, he said, is a luxury many other coastal areas don’t have, including large parts of Dubai’s mainland.
“If you look at a topographic survey you can see that with a high tide at [Dubai] creek you might get 1½m freeboard between the top of the water and the land. On the palm we’ve got 3m freeboard,” Lenehan said.
“In fact if you stand on our project at Mina Rashid, you can actually see that it is higher than the adjacent mainland.
“So if by the end of the century sea level rise did come up to the max forecast, large areas of Deira, the Creek and Bur Dubai would be underwater and Mina Rashid would still be above.”
Similarly, low lying cities and countries around the world will be battling for survival well before Nakheel’s Palms.
In 1987 the then president of the Maldives, Maumoon Abdul Gayoom, was famously quoted on his nation’s future.
“As for my own country, the Maldives, a mean sea level rise of 2m would suffice to virtually submerge the entire country of 1190 small islands, most of which barely rise 2m above mean sea level,” he said.
“That would be the death of a nation. With a mere 1m rise also, a storm surge would be catastrophic, and possibly fatal to the nation.”
The time lag
For several decades now small island nations around the globe have been making impassioned pleas to the developed world to cut greenhouse gas emissions to curb the rising seas.
This year a group of small island leaders put a resolution before the United Nations calling on the Security Council to tackle the issue as a threat to international peace and security.
But the horse may have already bolted with regards to saving our lowest lying coastal areas.
“The sea has been rising at about 3mm per year over the last decade and scientists expect that to accelerate along with the temperature of the globe,” said Hunter.
“This is obviously subject to what we do in terms of mitigating greenhouse gases but certainly for the first few decades or at least first half of this century that hardly affects sea level rises.
“There’s a big time lag effect here and there’s not much we can do about it. Once we really curb greenhouse gas emissions then we’ll have to wait decades, maybe centuries for sea level rise to flatten off.”
It’s a sobering thought and one which leads to the question, even if land reclamation projects are safe from sea rise this century, what will happen next century? At the rate things are going it seems likely most coastal development’s will face a watery future at some point.
While none of us will be around to see it, it’s a depressing thought that unlike the Pyramids of Egypt or India’s Taj Mahal these iconic developments of the 21st century may not stand the test of time for future generations.
