Future response of global coastal wetlands to sea level rise

The response of coastal wetlands to sea level rise (SLR) during the 21st century remains uncertain. Global-scale projections suggest that between 20% and 90% (for low and high SLR scenarios, respectively) of the present-day coastal wetland area will be lost, including the loss of biodiversity and highly valued ecosystem services1-3. These projections do not necessarily take into account allessential geomorphological4-7 and socio-economic system feedbacks8. Here we present an integrated global modelling approach that considers (i) the ability of coastal wetlands to build up vertically by sediment accretion and (ii) the accommodation space, namely the vertical and lateral space available for fine sediments to accumulate and to be colonised by wetland vegetation. We use this approach to assess global-scale changes in coastal wetland area in response to global SLR and anthropogenic coastal occupation during the 21st century. Based on our simulations we find that, globally, wetland gains of up to 60% of the current area are expected, if more than 37% of coastal wetlands have sufficient accommodation space, and sediment supply remains at present levels. In contrast to previous studies1-3, we project that until 2100 global coastal wetland loss will range between 0% and 30%, assuming no additional accommodation space. Our simulations suggest that global wetland resilience is primarily driven by the availability of accommodation space, which is strongly influenced by the building of anthropogenic infrastructure in the coastalzone and its expected to change over the 21st century. Rather than being an inevitableconsequence of global SLR, our findings indicate that large-scale coastal wetland loss might be avoidable, if sufficient additional accommodation space can be created through innovative “nature-based adaptation” solutions to coastal management.