̽��ֱ�� of Cambridge - Coastal defence

Sea change for Hull

lw355 — Fri, 16 Dec 2022 08:55:44 +0000

With a changing climate and rising sea levels putting cities at risk of flooding, it’s crucial for planners to increase their cities’ resilience. A new tool has been developed to help them – and it started with the throwing of a thousand virtual hexagons over Hull.

Sea Change

sc604 — Fri, 22 Mar 2019 09:13:26 +0000

̽��ֱ��coast is an intrinsic part of British identity – and perhaps nowhere is it more at risk than in the East of England. Cambridge researchers are working with communities and organisations across the region to manage the coast for the future, by working with nature rather than against it.

Opinion: Methods for protecting England’s coastal communities ‘not fit for purpose’

Anonymous — Wed, 07 Nov 2018 16:42:50 +0000

In October 2018, a stark report suggested that current methods being used to protect England’s coastal communities are ‘not fit for purpose’.

̽��ֱ��Committee on Climate Change’s Managing the coast in a changing climate report showed that between 2005 and 2014, over 15,000 new buildings were built in coastal areas at significant risk of coastal flooding and/or erosion.

However, if the government meets its ambitious housing targets, up to 90,000 homes built in the next five years might be in areas of significant annual flood risk from all sources of flooding, including coastal flooding.

Practically every winter we are reminded of how dynamic our coastline is. And many of us see at very close quarters how vulnerable many communities in the UK are to coastal flooding and erosion.

But by the time summer arrives, the need for a wide and deep debate as to how we deal with rising sea levels and potential future increases in maritime storminess around the UK coastline evaporates.

Our approach to coastal management issues is to react to failures of coastal defences, either natural or man-made, rather than proactively working towards future-proofing our coastline.

Much of the UK coastline is already eroding, as testified by the dominance of coastal cliff scenery. But coastal erosion and flooding, and consequent damage to infrastructure, disruption of services and modifications to the coastal landscape will become more common over the next century due to climate change.

Specifically, rising sea levels will increase the probability of extreme coastal water levels and this could be exacerbated by potentially larger and more frequent extreme waves due to changes to the wave climate.

At the same time, our coastal zone is far from natural, with numerous clifftop properties and extensive development at the back of beaches, on top of dunes and in low-lying coastal valleys. It is obvious that coastal communities are facing significant future challenges.

Much existing coastal development took place when our understanding of coastal dynamics was limited and when climate change, and its consequences for the coast, was not yet a reality.

That development is already under threat, and the scale of the threat will only increase. Dealing with this issue requires a balanced consideration of the various adaptation strategies, ranging from ‘hard’ coastal protection such as sea walls to more sustainable solutions such as supplementing the amount of sand and gravel on our beaches, and managed realignment.

There will always be locations where only hard coastal defences will do.

But if we wish to avoid piling ever-increasing costs – in both financial and environmental terms – on future generations, we need a more sophisticated, integrated discussion of zoning (to avoid building in high-risk zones).

It may be stating the obvious, but a relatively easy win is to avoid more development in the dynamic coastal zone unless it is absolutely essential.

̽��ֱ��concept of Coastal Change Management Areas (CCMAs) can play a key role here.

̽��ֱ��National Planning Policy Framework (NPPF) requires councils to identify CCMAs where rates of shoreline change are expected to be significant over the next 100 years, taking account of climate change.

̽��ֱ��first local plan to make use of CCMAs to inform coastal planning is in Cornwall, where the Newquay Neighbourhood Plan (NNP) is currently under consultation.

̽��ֱ��NNP recommends that proposals for development in CCMAs should only be supported where they are for “small, temporary structures that will not add to the erosion risk”, and rules out residential development.

Proposals for redevelopment, enlargement or extension of existing buildings that fall within the exclusion zone, and proposals to change the use of existing buildings into residential usage, will not be supported either.

In the NNP, the landward limit of CCMAs represents the estimated 100-year erosion line with an additional buffer of 10 metres. Another 2m buffer zone is added if the coastal path is located within the CCMA.

Continued investment into the coastal zone will reduce the natural capability of the coast to respond to hazards, while at the same time passing the financial burden of protecting such coastal development onto future generations.

In order to future-proof our dynamic coast, we need to implement an appropriate buffer zone to inform coastal planning decisions, and these buffer zones will need to be site-specific and science-based.

They would also require regular updating in light of new data, understanding and predictions of climate change and its consequences.

̽��ֱ��Committee on Climate Change’s report has demonstrated the scale of future potential problems, and our own research heavily supports their findings.

By implementing a CCMA-informed policy that is consistent on a national scale, potentially with the policy outlined in the NNP as a blueprint, we can better protect our coastlines now and for future generations.

A bold response to the world’s greatest challenge
̽��ֱ�� ̽��ֱ�� of Cambridge is building on its existing research and launching an ambitious new environment and climate change initiative. Cambridge Zero is not just about developing greener technologies. It will harness the full power of the ̽��ֱ��’s research and policy expertise, developing solutions that work for our lives, our society and our biosphere.

Professor Tom Spencer from Cambridge’s Department of Geography and Professor Gerd Masselink from the ̽��ֱ�� of Plymouth say evidence suggests there should be far stricter controls on coastal developments.

Christopher Martin

Teignmouth seafront

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Up to four-fifths of wetlands worldwide could be at risk from sea level rise

sc604 — Wed, 24 Feb 2016 08:38:49 +0000

Using a new model to measure the possible effects on wetlands on a global scale, the researchers, from the UK and Germany, modelled the impacts of different scenarios for sea level rise to the end of this century.

They found that even in the event of ‘low’ global sea level rise (around 30 centimetres), much of the world’s wetlands, particularly on ‘micro-tidal’ coasts, are vulnerable. Around 70 percent of the world’s wetlands are found on micro-tidal coasts, where the range between high spring tide and low spring tide is less than two metres, such as in the Mediterranean and the Gulf of Mexico. ̽��ֱ��results are reported in the journal Global and Planetary Change.

Across the globe, wetlands cover more than 750,000 square kilometres, an area more than three times the size of the UK. Coastal wetlands, which include salt marshes, mangrove forests and mud flats, protect against erosion and flooding, provide habitat and food for wildlife, improve water quality, support commercial fisheries, and can store large amounts of carbon.

“Wetlands are particularly sensitive to environmental change, and are being lost worldwide due to human activity, such as conversion to agriculture, and through the effects of climate change, including rising sea levels,” said Dr Tom Spencer of the ̽��ֱ�� of Cambridge’s Department of Geography, the paper’s lead author.

According to the Intergovernmental Panel on Climate Change (IPCC), it is very likely that sea levels will rise during the 21^st century, but by how much depends on a variety of factors, including thermal expansion caused by ocean warming, loss of ice in glaciers and ice sheets, and the reduction of liquid water storage on land.

̽��ֱ��Wetland Global Extent Index, published in 2014, estimates that between 1970 and 2008, natural coastal wetlands declined by nearly 50 percent. A main reason for the high vulnerability of coastal wetlands to sea level rise is coastal ‘squeeze’, a consequence of long-term coastal protection strategies, such as dikes. While dikes provide flood defence to coastal populations and infrastructure, they prevent wetlands from moving landwards and upwards: dikes leave them with nowhere to go.

Wetlands such as salt marshes are made up of grasses and shrubs and are sensitive to environmental change, whereas wetlands such as mangrove forests, since they are trees, are far more resilient, at least in the short term.

Previous attempts to quantify the risk to wetlands posed by rising sea levels have focused on small areas, or have only looked at wetlands being lost through ‘drowning’ of the plants and shrubs, and not at how wetlands will ‘migrate’ inland.

̽��ֱ��model that Spencer and his collaborators from the ̽��ֱ�� of Southampton and Middlesex ̽��ֱ�� in the UK, and the Geographisches Institut and the Global Climate Forum in Germany, have developed assesses biophysical and socio-economic consequences of sea level rise and socio-economic development, taking into account coastal erosion, coastal flooding, wetland change and salinity intrusion.

̽��ֱ��researchers used their model to look at three different sea level rise scenarios (low, medium and high), combined with different scenarios for dike construction (no dikes, widespread dikes and maximum dikes), and assessed what the effect on coastal wetlands would be for each.

They found that if global sea levels rise by 100 centimetres combined with maximum dike construction, global wetland losses may reach 78 percent. For a rise of 50 centimetres, between 46 and 59 percent of coastal wetlands could be lost. For sea level rise around 30 centimetres, wetlands in micro-tidal regions are the most vulnerable.

“What our model does is provide better-informed projections about what might happen to wetlands over the coming century on a global scale,” said Spencer.

One of the issues which the researchers looked at was the use of dikes, seawalls, levees and other forms of coastal protection, and finding the balance between protecting cities and infrastructure from flooding, and protecting the wetlands which also play a key role in flood defences.

“One of the key things this project shows is that we need integrated management of wetlands and coastal protections on a national and international scale,” said Spencer. “Because if you don’t, in many cases if you protect one section of the coast, all you’re doing is moving the problem somewhere else.”

Countering these potential wetland losses will require both global responses such as climate mitigation to minimise sea level rise, and regional responses such as the maximisation of accommodation space and sediment supply on low-lying coasts.

̽��ֱ��researchers have already begun working on the next version of their model, which will also consider the effect that storms have on wetlands.

̽��ֱ��research was supported in part by the European Union.

Reference:
Thomas Spencer et. al. ‘Global coastal wetland change under sea-level rise and related stresses: ̽��ֱ��DIVA Wetland Change Model.’ Global and Planetary Change (2016). DOI: 10.1016/j.gloplacha.2015.12.018

Researchers have modelled how wetlands might respond to rising sea levels, and found that as much as four-fifths of wetlands worldwide could be lost by the end of the century if sea levels continue to rise.

We need integrated management of wetlands and coastal protections on a national and international scale.

Tom Spencer

By Anthony Bley, U.S. Army Corps of Engineers [Public domain], via Wikimedia Commons

Wetlands in Cape May, New Jersey, USA

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Salt marsh plants key to reducing coastal erosion and flooding

sc604 — Thu, 02 Oct 2014 10:07:00 +0000

̽��ֱ��effectiveness of salt marshes – wetlands which are flooded and drained by tides – in protecting coastal areas in times of severe weather has been quantified in a study by researchers from the ̽��ֱ�� of Cambridge.

In the largest laboratory experiment ever constructed to investigate this phenomenon, the researchers have shown that over a distance of 40 metres, the salt marsh reduced the height of large waves in deep water by 18%, making them an effective tool for reducing the risk of coastal erosion and flooding. Sixty percent of this reduction is due to the presence of marsh plants alone. ̽��ֱ��results are published in the journal Nature Geoscience.

One of the most noticeable effects of climate change is the increasing frequency and severity of storms, such as the series of storms which battered parts of south west England last winter. As the climate continues to warm and sea levels continue to rise, the effects of these storms could be devastating, putting these and other coastal communities worldwide at risk.

While the important role of salt marshes in protecting against coastal erosion is well-known, their effectiveness in mitigating the effects of extreme weather, when water levels are at their maximum and waves are at their highest, had not been understood or definitively quantified.

Recreating a salt marsh in a large wave tank and subjecting it to realistic storm conditions, the researchers found that it significantly ‘buffered’ the effects of the waves. Similar to wind blowing through a forest, the plants reduce the energy of the water as it flows through and around them. Even when the waves flattened and broke the marsh’s vegetation, the soil surface beneath remained stable and resistant to surface erosion.

Salt marshes are found throughout the world, particularly at middle to high latitudes. In addition to their role in protecting against coastal erosion and reducing flooding, they also act as nurseries and refuges for many species of marine animals, and protect water quality by filtering runoff.

Given increased rates of global sea level rise, there are concerns about losing salt marsh on many coasts, particularly where there is insufficient sediment and space to allow marshes to build upwards and landwards.

“While we have long known that salt marshes and other natural defences such as sand dunes or mudflats can help protect our coastlines, a lack of data on their effectiveness in extreme conditions has meant that they often are not included in flood risk assessments,” said Dr Iris Möller of Cambridge’s Department of Geography (Cambridge Coastal Research Unit), who led the research. “But we’ve shown that even in extreme conditions, salt marshes are a vital defence for our coastlines and protect against more frequent storms.”

̽��ֱ��researchers used large sections of salt marsh, cut from a natural marsh in northwestern Germany. ̽��ֱ��team then rebuilt the marsh in one of the world’s largest wave tanks, located in Hannover, and subjected it to water depths and types of waves that are typical in storm surge conditions. Even after the waves flattened the plants, the marsh was still an effective barrier against erosion, demonstrating the importance of natural flood defences alongside manufactured defences such as flood walls.

̽��ֱ��flooding which hit south west England last winter was the worst in nearly 20 years. A series of 12 major storms between December and February caused huge waves, strong winds and hide tides to pummel large parts of Cornwall, Devon and the southwest, causing millions of pounds worth of damage. Many homes and businesses were flooded multiple times, and major flooding in the Somerset Levels forced many families to evacuate their homes and many farmers to evacuate their livestock.

As part of the government’s attempts to mitigate the effects of future storms, salt marshes have been re-created in several locations around the UK coast: a large new salt marsh on the Somerset’s Steart peninsula was recently completed, and several more are planned for locations throughout the UK.

̽��ֱ��research was supported by the European Community’s 7th Framework Programme and a grant from ̽��ֱ��Isaac Newton Trust, Trinity College, Cambridge.

̽��ֱ��researchers are blogging about their work at thesaltmarshexperiment.wordpress.com.

Study finds that natural flood defences such as salt marshes can reduce the height of damaging waves in storm surge conditions by close to 20%.

Even in extreme conditions, salt marshes are a vital defence for our coastlines

Iris Möller

James Tempest

Storm on a rising tide, Orplands, Essex

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Cambridge researchers learn lessons from recent storm surge

jfp40 — Thu, 16 Jan 2014 12:20:31 +0000

̽��ֱ��wet and windy weather that has battered Britain’s coasts this winter has brought misery to many, but for researchers at the ̽��ֱ�� at Cambridge the storm damage is providing vital data that could help improve future flood warnings and emergency planning.

On 5 December 2013, coastal communities along the North Norfolk coast were threatened by a significant storm surge – the result of low atmospheric pressure (which causes sea level to rise) combined with high winds pushing up the sea surface as they blow water towards the coast.

According to Dr Tom Spencer of the Department of Geography’s Cambridge Coastal Research Unit: “ ̽��ֱ��southern North Sea is very vulnerable to storm surges because of its shallow water, and winds blowing from north to south funnel the sea into the narrowing basin near the Straits of Dover.”

Predicting the impact of storm surges on coastal areas like North Norfolk, which is lined with barrier islands and gravel spits – and cut by tidal inlets bordered by mudflats and saltmarshes, is challenging. To find out how these features affected the water levels and waves that hit the area’s coastal settlements during the storm, the team from Cambridge and Birkbeck, ̽��ֱ�� of London took to the road.

Immediately after the surge, they travelled the 45km between Holme-next-the-Sea and Salthouse measuring maximum water levels with a satellite-based survey system able to resolve positions and heights to an accuracy of less than 50mm and often less than 20mm. “We looked for debris lines, erosion marks on earthen banks and floodlines on buildings – or in some cases car windscreens,” Dr Spencer explained.

They found that maximum surge heights here differed by almost 2m, depending on whether the site was exposed or sheltered, differences much larger than previously thought. “At some sites this was the critical difference between a business or a home being flooded or not,” said Dr Spencer. If these results can be incorporated into surge models and flood forecasts, they could help improve early warning systems and evacuation planning.”

̽��ֱ��December 2013 event that Dr Spencer studied came almost exactly 60 years after the disastrous storm that hit the region in 1953, claiming more than 2,000 lives around the southern North Sea – the largest death toll from flooding in Europe for 100 years.

“Looking at the atmospheric pressure charts, the 2013 and the 1953 events look similar: both were characterised by a deep low pressure system that came down the long axis of the North Sea. But while the 2013 storm was short-lived, producing waves of around 3.8m offshore from North Norfolk, in 1953 gale force winds blew for several days ahead of the surge, producing waves probably close to 8m high off eastern England,” he says.

Like the 2013 event, the 1953 storm arrived under cover of darkness. But unlike 2013, it hit over the weekend, with devastating results.

“Most people in the UK and ̽��ֱ��Netherlands were asleep in bed when floodwaters broke into their houses, many of which were single storey chalets and bungalows. Some people managed to get onto their roofs but, with the storm still raging, they died from exposure or slid into the sea,” he said. “In ̽��ֱ��Netherlands, where over 1,800 lives were lost, the radio ceased transmitting at midnight on the Saturday and although warnings were issued by telegram, these arrived at offices that were shut over the weekend.”

Much was learned from the 1953 storm: coastal defences were heightened and strengthened, and there have been major advances in storm surge forecasting and emergency planning. But, as Dr Spencer’s results show, there are still lessons to be learned from today’s floods that could help prevent tomorrow’s victims.

̽��ֱ��team’s initial assessment is published in Nature.

For researchers at the ̽��ֱ�� at Cambridge, recent storm damage is providing vital data that could help improve future flood warnings and emergency planning

These results could help improve early warning systems and evacuation planning

Tom Spencer

I Moeller

Stranded boat at Blakeney after storm surge

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Yes

Good tidings for coastal communities

sj387 — Wed, 23 Oct 2013 09:00:49 +0000

Flooding from rising sea levels and extreme weather events is a major global issue, and the UK is no exception. According to the Government’s 2012 Climate Change Impact Risk Assessment, flooding is the greatest threat facing the UK today.

̽��ֱ��UK’s current strategy for coastal defence is largely reliant on rigid structures such as sea walls. Many of these are reaching the end of their design life, and proving disadvantageous in terms of cost, restrictive access to the sea and limited capacity to adapt to rising sea levels.

As for the longer term, the Future Foresight flood research project commissioned by government and published in 2004, concluded that the government’s 100-year shoreline defence plans were not adaptive enough to cope with changes expected within the next 15 to 30 years.

But how can walls and buildings – which we take for granted as solid, enduring structures – adapt to a landscape that is gradually changing from firm ground to wetlands to sea? Does such an adaption require a sea-change in our own attitudes to permanence in our built environment?

Ed Barsley, who completed a Master’s in Architecture and Urban Design last year in the ̽��ֱ�� of Cambridge's Department of Architecture and has now started a PhD, believes it does, and has come up with an adaptive, flexible approach to coastal flooding as innovative in design and technological terms as it is sensitive in cultural ones.

“I aimed to design a town that is intrinsically able to inhabit this increasingly flood-prone landscape,” he said. “It is characterised by two distinctive features. ̽��ֱ��first is a multi-layered threshold that combines soft and hard defences. ̽��ֱ��second is that every one of these thresholds is permeable by the sea.”

Barsley based his study in the town of Par near St Austell, inspired by a year spent building and designing eco-houses in Cornwall. Shortlisted for the Government’s now defunct Eco-town scheme, Par has been earmarked as a future key commercial and transport hub for the region. Yet it is at high risk of flooding.

Barsley’s concept starts not in the town itself, but out at sea. Wave attenuation devices would divert the waves’ energy, and harness it to power the town. A zone of coastal nourishment, created by spraying sediment on the sea bed, would then graduate the force of the waves and help dissipate their power. Next, a series of interconnected saline lagoons would help to further reduce the waves’ crest height and velocity, as well as provide vital wildlife habitats.

It would only be at the harbour that the sea meets a wall – and one with a difference. “My sea wall, which also acts as a social causeway, is perforated, its apertures work to diffuse the flow of the waves before they enter the harbour,” said Barsley. ”It has been designed to provide access to the water’s edge at a variety of height levels depending on the tides. Like the Thames Barrier, it could lock down and close up during extreme weather conditions.”

̽��ֱ��town itself is designed on the same principle as the permeable sea wall. “Buildings designed to act as buffers are juxtaposed with ones designed to let the water through, so as to enable the people of Par to maintain use of some buildings during a flood event” said Barsley. “Furthermore, because the apertures of the porous buildings are smaller at the front than at the back, the varied configuration of buildings would mean that the streets themselves act like the sea wall, further attenuating the turbidity of the water.”

Par is situated on ground that slopes up from the sea. ̽��ֱ��planning of Barsley’s town takes advantage of this. Organised on the basis of phased inhabitation zones, a range of street levels provides shelter and access routes, with essential services on highest ground.

This results in a main high street that is not only a refuge but is quintessentially Cornish in style and atmosphere. It is peppered with lateral access routes – narrow twisting lanes, winding staircases and inclines – that lead down to the harbour and afford tantalising glimpses of the sea. This charming, higgledy-piggledy style (or ‘Cornish vernacular’ as it known to architects) has emerged from Barsley’s strategic response to the need for resilience, rather than being a pastiche.

Despite its resilience, large portions of Barsley’s town would, eventually, become submerged: current data from the Intergovernmental Panel on Climate Change predicts that Par will be flooded on a daily basis by 2100. Barsley’s design caters for a future beyond this point. “Once submerged,” he said, “the town as a whole would form a major water-calming device in the same way as the other permeable thresholds, by both obstructing and attenuating the waves. As wetlands form in the area behind the town, the water would, I hope, be sufficiently calm to accommodate floating homes and amphibious technologies proven in their efficacy on still water, but unsuited to choppy sea-water.”

̽��ֱ��fundamental principle behind Barsley’s design for Par is that it should enable its residents to live in harmony with the ebb and flow of the sea. To an extent, they already go with the flow: the tides in Par fluctuate by 4.5 metres on an average day.

As well as adapting to the tides in pragmatic terms, however, Barsley believes that a fundamental shift in cultural attitudes towards the idea of possession of property is needed, because gradually, but inexorably, the sea is re-possessing the land. So Barsley’s design is based on the assumption of a policy of 50-year leasehold land parcels to underpin the strategy of Phased Inhabitation Zones. “A ground floor unit by the waterfront might start off life as a café or an artist’s studio,” he explained, “but after 50 years might need, for instance, to turn into a boatshed or a store. And at some point that unit will have to be abandoned and left to function as a defence threshold. We have to change our attitudes towards possession and risk, and stop fighting a losing battle with nature.”

Barsley begins his thesis with H G Wells’ prescient warning written in 1945: ‘Adapt or perish, now as ever, is nature’s inexorable imperative’. Barsley, and his fellow students and graduates of the Department of Architecture at Cambridge, are responding to the challenge.

Koen Steemers, Professor of Sustainable Design and Head of the Department of Architecture, said: “Ed’s project exemplifies design research that builds on the latest multidisciplinary research expertise to synthesise and test an imaginative design in response to pressing environmental issues. Because of the real potential application of such projects, recognised by the architectural profession, developers and policy-makers worldwide, we are now looking into setting up an enterprise advisory scheme to help realise such innovative and necessary visions of architecture.”

You can find more information about the pioneering work of students in Architecture and Urban Design including details of Ed Barsley’s project.

̽��ֱ��sea sustains life but also threatens it. An innovative design concept by Ed Barsley aims to contend with rising seawater by welcoming it into our coastal settlements.

We have to change our attitudes towards possession and risk, and stop fighting a losing battle with nature

Ed Barsley

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Mangroves could survive sea-level rise if protected

tdk25 — Wed, 31 Jul 2013 07:44:32 +0000

Mangroves, which provide a natural coastal defence to communities around the world, may be able to withstand a future rise in sea levels far more than previously thought, scientists have found.

Their report should serve to allay fears that many mangrove areas could be lost in the coming decades as sea levels go up because of global warming.

It comes, however, with a cautionary note: ̽��ֱ��authors, who have carried out a rare and detailed survey of how mangroves adapt to their environment, also argue that it is vital that they are managed and conserved so that they can continue to provide this protection.

̽��ֱ��survey warns that human activity on land – such as the damming up of rivers or the felling of trees to create shrimp ponds – is currently a far greater threat to many mangrove habitats than the effects of climate change on sea level.

Mangroves – trees and shrubs which grow in saltwater, coastal environments – play a critical role in protecting thousands of shoreline communities in tropical and subtropical regions from floods, storms, and other hazards.

Their densely-packed, overground root systems can absorb wave energy and reduce the velocity of a sudden surge of water. In the 2004 tsunami, for example, mangroves were sometimes the difference between life and death for people whose homes lay in the path of the giant waves which crashed into shorelines around South Asia.

For some time, scientists have been concerned that if sea levels rise as predicted, they will kill off mangroves – removing these natural coastal defences at the very time they are expected to be needed most.

̽��ֱ��new study suggests that this is far less likely than previously thought, however. Dr Anna McIvor, from the ̽��ֱ�� of Cambridge, and the report’s lead author, said: “Although we can expect some mangrove areas to be lost as sea levels rise, many of them appear to be able to withstand it.”

“In fact, changes to mangrove habitats through human activity are likely to pose a bigger threat to these coastal defences than sea level rise as it stands. Our research has enabled us to find out more about how mangroves continue to flourish in spite of a rise in sea levels – but that information should be used as the basis for better management of these important ecosystems.”

̽��ֱ��study was carried out by a team from ̽��ֱ��Nature Conservancy, Wetlands International, and the Cambridge Coastal Research Unit (based in the ̽��ֱ��’s Department of Geography). ̽��ֱ��researchers examined both recent reports looking at surface elevation in mangrove areas, and the historical reasons why mangroves have, in some places, persisted for thousands of years.

They found that the height of the soil surface in mangrove areas is often “surprisingly dynamic”, and in some cases appears to be building up at rates of between one and 10 millimetres every year. ̽��ֱ��global mean sea level rise is currently 3mm per year, meaning that many mangrove areas build up soil at a rate which keeps pace with the sea.

There are several reasons for this, but chief among them appear to be the ability of mangroves to trap sediment as it is carried down to them by rivers, and the work of their roots beneath the surface. “Mangroves provide much of the organic sediment matter that makes up the soil, their complex roots help to bind and trap the sediments on the soil surface, while the unseen growth of roots beneath helps to build up the soil from below,” McIvor said.

Despite this resistance to changes in sea level, however, the report cautions that the future stability of mangroves is by no means guaranteed. “Threshold rates of sea level rise are likely to exist, beyond which mangrove surfaces are no longer able to keep up,” the authors point out.

Perhaps more urgently, in some regions human activities like agriculture and construction are being authorised regardless of their impact on the ecosystems which enable mangroves to thrive.

In some countries, for example, rivers which play a vital role by carrying sediment to the mangrove areas so that the soil can be built up are being dammed or diverted. Another common threat is aquaculture: in Indonesia, and other South Asian countries, mangroves are often cut down without restriction to make way for shrimp ponds.

̽��ֱ��report also warns that mangroves may need room to expand landward, especially where conditions are such that sea level rise may still be a threat to their growth. Communities which rely on them for coastal defence need to leave space to ensure that this can happen, the authors advise.

Dr Mark Spalding, from ̽��ֱ��Nature Conservancy and the Department of Zoology, ̽��ֱ�� of Cambridge, said: “This report shows that well-managed mangroves in many places will continue to support and safeguard many vulnerable communities as sea levels rise. We still have lots to learn about them, but the sensible, precautionary approach is to look after them and restore them as a critical first line of defence.”

̽��ֱ��full report can be downloaded at: http://coastalresilience.org/science/mangroves/surface-elevation-and-sea...

For more information about this story, please contact Tom Kirk, Tel: 01223 332300, thomas.kirk@admin.cam.ac.uk

Human activity is currently a bigger threat to mangroves, and the natural defences they provide against storm surges and other coastal disasters, than rising sea levels, according to a new study.

Although we can expect some mangrove areas to be lost as sea levels rise, many of them appear to be able to withstand it.

Anna McIvor

Wikimedia Commons.

Mangrove trees along a coastline, Everglades National Park.

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Yes