Spatial distribution of coastal wetland change by the year 2100 under sea level rise from global warming. Graphic: Schuerch, et al., 2018 / Nature

13 September 2018 (University of Southampton) – A new global study involving researchers from the University of Southampton suggests coastal wetlands, such as those on the South Coast of England, can survive rising sea levels and continue to provide natural defence from flooding if they are able to migrate further inland.

Coastal wetlands, which include saltmarshes, mudflats and mangroves are found widely around the world’s coastlines. They provide productive habitats for wildlife and protect local communities from flooding and coastal erosion. Wetlands are declining around the world and rising sea levels are expected to increase the rate of these losses. However this new research shows that if coastal wetlands are given space to expand, they can adapt to rising sea levels and continue to protect coastal communities from the effects of climate change.

These findings will have particular implications for the South Coast. Saltmarshes are widely found in front of seawalls and dikes in estuaries such as the Solent or Poole Harbour and are declining. A number of projects in the region have seen manmade defences removed or relocated to restore the natural flood defence provided by wetlands. Schemes have been implemented around Chichester Harbour, at Thorness Bay on the Isle of Wight, the Rother, East Sussex and most notably the large project at Medmerry near Selsey Bill. Further schemes are being implemented or are planned in the coming decades.

Whilst schemes such as these can face local opposition, the study’s authors are calling for this natural approach to protecting the coast to be considered more widely. To build on this global study, more monitoring is needed locally to ensure that coastal engineers have the information they need to minimise the risk of flooding.

Professor Robert Nicholls from the University of Southampton who co-authored the report said: “This paper fundamentally challenges the existing consensus about the future of coastal wetlands under sea-level rise. It suggests that nature-based approaches to defence in coastal zones are sustainable and we should maximise the benefits of them as much as we can.”

Dr Sally Brown and Dr Mark Pickering completed the team from the University of Southampton. The global study was led by the University of Lincoln and included researchers from universities in Germany, Australia and the USA.

The full paper, Future responses of global coastal wetlands to sea level rise, has been published in the scientific journal Nature.

Wetlands across England’s south coast need to move inland in fight against climate change


ABSTRACT: The response of coastal wetlands to sea-level rise during the twenty-first century remains uncertain. Global-scale projections suggest that between 20 and 90 per cent (for low and high sea-level rise scenarios, respectively) of the present-day coastal wetland area will be lost, which will in turn result in the loss of biodiversity and highly valued ecosystem services1,2,3. These projections do not necessarily take into account all essential geomorphological4,5,6,7 and socio-economic system feedbacks8. Here we present an integrated global modelling approach that considers both the ability of coastal wetlands to build up vertically by sediment accretion, and the accommodation space, namely, the vertical and lateral space available for fine sediments to accumulate and be colonized by wetland vegetation. We use this approach to assess global-scale changes in coastal wetland area in response to global sea-level rise and anthropogenic coastal occupation during the twenty-first century. On the basis of our simulations, we find that, globally, rather than losses, wetland gains of up to 60 per cent of the current area are possible, if more than 37 per cent (our upper estimate for current accommodation space) of coastal wetlands have sufficient accommodation space, and sediment supply remains at present levels. In contrast to previous studies1,2,3, we project that until 2100, the loss of global coastal wetland area will range between 0 and 30 per cent, assuming no further accommodation space in addition to current levels. Our simulations suggest that the resilience of global wetlands is primarily driven by the availability of accommodation space, which is strongly influenced by the building of anthropogenic infrastructure in the coastal zone and such infrastructure is expected to change over the twenty-first century. Rather than being an inevitable consequence of global sea-level rise, our findings indicate that large-scale loss of coastal wetlands might be avoidable, if sufficient additional accommodation space can be created through careful nature-based adaptation solutions to coastal management.

Future response of global coastal wetlands to sea-level rise

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