Establishing a global database of surface elevation change and accretion rates in coastal wetlands

The effects of rising sea-levels on coastal regions and the increased vulnerability of the coastal zone due to the high concentration of natural and socio-economic resources highlight the need for regional to global assessments. Global vulnerability assessment (GVA) studies have been the main sources of quantitative information on the potential impacts of sea-level rise. However, one of the principal limitations of GVAs, which has compromised their reliability and consistency, has been the lack of appropriate data sources. To fill this significant gap in coastal research, a new global coastal database has been developed within the framework of the EU DINAS - COAST project. The database provides the input data for the Dynamic Interactive Vulnerability Analysis (DIVA) tool which is the main product of the project. DIVA has been designed to assess impact and vulnerability of the coastal zone to sea-level rise at regional to global scales and is driven by a set of internally consistent 'mid-term' (until 2100) scenarios of sea-level rise and socio-economic drivers of societal sensitivity to plausible impacts of accelerated sea-level rise and adaptive capacity. DIVA identifies coastal units that are particularly vulnerable to sea level rise and adverse human interventions and allows for the evaluation of a range of response options.

The DIVA database has been designed to include data on physical, ecological and socio-economic characteristics of the coast at various resolutions and covers all the world's coastline, excluding Antarctica. Given the linear nature of the coast, all the data in the DIVA database are referenced to linear coastal segments (Figure 1) and are expressed as attributes of five main geographic features: (a) coastline segments, (b) administrative units, (c) countries, (d) rivers, (e) tidal basins. This gives a fundamentally different data structure compared to the more common raster datasets used in global studies.

Figure 1 An example of the coastline segmentation. Coastline segments for Europe and associated information (from Vafeidis et al., 2004).

Nested within DINAS - COAST is a wetland loss and change module (Figure 2)

Figure 2 Schematised methodology of DINAS - COAST.

The Wetland Change Model incorporates a number of physical (e.g. tidal range and sediment supply) and socio-economic forcing factors (e.g. removal of accommodation space by building seawalls and dikes). These factors are weighted to give a wetland vulnerability score (Figure 3). This vulnerability score is then transformed into a measure of ecological sensitivity; the model recognises that the response of a wetland to environmental stresses is not necessarily immediate. Rather, it is likely to be due to a combination of current and previous ecological states. This time lag between a forcing event and its geomorphological and/or ecological expression is dependent on habitat type. Finally, ecological sensitivities are converted to changes in wetland type and/or wetland loss to open water through a wetland transition model (Figure 3).

Figure 3 The Wetland Change Model (from McFadden et al., in review)

An example of model outputs is shown for potential changes in wetland extent for the State of Florida, USA (Figure 4).

Figure 4 Scenario of predicted wetland transitions 2000 - 2060 within the State of Florida, USA as predicted by the DIVA Wetland Change Model (From McFadden et al., in review).

Whilst the Wetland Change Model provides an improved broad-scale model of loss and transition of coastal wetlands under sea-level rise, a major challenge remains in the validation of model results. The development of more systematic national to regional scale assessments of wetland behaviour would contribute significantly to validating the Model and hence, refining global estimates of wetland loss. Sedimentation Erosion Table (SET) measurements as described by Cahoon et al., (1999) have begun to generate a large dataset of vertical marsh elevation change over time to a range of environmental forcings. This standard approach offers the possibility of detailed site-specific information that might then be applied to similar wetlands to better measure the vulnerability of wetlands worldwide. As yet, the data network is concentrated in the USA, the Caribbean, Europe and the western Pacific and the measurement time series are relatively short at most locations. Nevertheless, the network is now of sufficient maturity to allow the first steps (as reported at the INTECOL meeting in Utrecht in 2004) to be taken in developing a multi-regional and global assessment of wetland responses to sea-level rise.

Publications

• McFadden, L., Spencer, T.S. and Nicholls, R.J. (in review) Broad-scale modelling of coastal wetlands: what is required? Hydrobiologia.

Published conference proceedings

• McFadden, L., Spencer, T. and Nicholls, R.J. (in press) Coastal Wetland Loss and Climate Change: Towards a Global Perspective. In: COASTWETCHANGE, Lagoons and Coastal Wetlands in the Global Change Context: Impacts and Management Issues, Venice 2004. UNESCO : Paris.
• McFadden, L., Spencer, T. and Nicholls, R.J. 2005 Identifying Vulnerable Wetland Systems: Modelling the large-scale response of wetlands to sea-level rise. In Wallendorf, L., Ewing, L., Rogers, S. and Jones, C. (Eds.), Solutions to Coastal Disasters 2005, 453-465. ASCE : Reston, VA.
• Vafeidis, A.T., Nicholls, R.J., Boot, G., Cox J., Grashoff, J.P., Hinkel, J., Maatens, R., McFadden, L., Spencer, T. and Tol, R.S.J. 2004 A global database for coastal vulnerability analysis (DINAS COAST). LOICZ Newsletter 33: 1-4.

Conference abstracts

• McFadden, L., Spencer, T. and Nicholls, R.J. 2005 A new model of wetland loss and sea-level rise. LOICZ II Inaugural Open Science Meeting, Egmond an Zee, Netherlands, 27-29 June 2005.
• Spencer, T., Cahoon, D.J., Day J.W. Jr. and French, J.R. 2004 Trends in surface elevation change of European and North American salt marshes. 7^th INTECOL International Wetlands Conference, Utrecht, The Netherlands, Abstracts Volume.

Collaboration

• Dr L McFadden, Flood Hazard Research Centre, Middlesex University, UK
• Professor RJ Nicholls, Southampton University, UK
• Dr JR French, University College London, UK
• Professor R Klein, Potsdam Institute for Climate Impact Research, Germany
• Dr D Cahoon, US Geological Survey, Maryland, USA
• Professor JW Day Jr, Louisiana State University, USA
• Professor DJ Reed, University of New Orleans, UK

DINAS-COAST is an IGBP-LOICZ Regional Project.

Funding

The initial project was funded as part of the EU DINAS-COAST project under the Fifth Framework Programme Thematic Priority 'Mitigation and Adaptation to Global Change'. The project number was EVK2-2000-22024.