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The Impact of Sea Level Rise on Coastal Wetlands

map showing coastal ramsar wetlands sites in Mexico at risk from 0-1 meter sel level rise

This map depicts the relative risk of wetland loss from sea level rise in coastal areas of Mexico, as part of an analysis for Ramsar Wetlands of International Importance. The Ramsar Convention is an international treaty that seeks to safeguard aquatic ecosystems by protecting specific wetland sites of high value. The map shows several sites with large percentages of land area currently above sea level that are at risk of being partially submerged by a 1-m sea level rise. (Sites are labeled if they are at risk of losing greater than 32% of their land area to a 1-m rise in mean sea level.)  Sea level has risen and is expected to continue to rise mostly as the result of melting of land based glaciers and ice sheets, as well as thermal expansion of ocean water. Both processes are tied to temperature increases associated with global warming. Experts indicate that sea levels could rise by as much as a meter in this century.

There are 133 Ramsar sites in Mexico, of which 77 are at some risk of losing land to a 1-m sea level rise.  The largest Mexican site at relatively high risk is the Biosphere Reserve (Reserva de la Biosfera) Pantanos de Centla in Tabasco State (see inset). This site features seasonally flooded moist forests with associated wetlands (bogs, swamps, and neighboring mangroves). Roughly 62% of the land area that is currently above sea level is at risk from a 1-m rise.

Globally, coastal Ramsar sites feature a number of important ecosystems, including coral reefs, sea grass beds, mangroves, and estuaries. Because they lie at current sea level, they are at risk of inundation (flooding) from sea level rise and associated phenomena such as storm surge, when a coastal storm causes water to rise to abnormally high levels. Although coastal wetlands are themselves an important natural buffer to storms, sea level rise will put new stress on them, and potentially displace them inland. Just how far inland these wetlands can “migrate” depends on what surrounds them, whether natural features such as hills or plains or manmade features such as roads, settlements, croplands, or infrastructure.

In this analysis, conducted for the Ramsar Convention’s Scientific and Technical Review Panel (STRP) by the Earth Institute’s Center for International Earth Science Information Network (CIESIN), the risk of wetland loss is first assessed by evaluating the elevation of Ramsar sites to see what percentage of a site’s area above sea level is at risk of inundation under different sea level rise scenarios. We then evaluated each site’s ability to migrate inland given human population density and urban areas in and around the site.

Globally, we found that 85% of 1,143 coastal sites (evaluating only those sites with adequate spatial boundary data that are contiguous with the coastline), or 971 sites, are at risk due to sea level rise. This suggests a need to begin planning for adaptation measures, such as ensuring that wetlands have the ability to move inland with rising waters.

This first-order assessment has a number of limitations. We used NASA’s Shuttle Radar Topography Mission (SRTM) data to estimate the area at risk, which is the best available global elevation data set, but which has some limitations in vertical accuracy and may pick up tree-tops in areas with dense vegetation.  Sea level rise will not be consistent globally, but will be affected by coastal bathymetry (the depth of the water offshore), local topography, and tides. There will also be secondary impacts of sea level rise, such as the displacement of human populations and agricultural activities and the salinization of aquifers, which could have additional consequences for wetland and biodiversity loss. Although this exercise has served to identify high risk sites, we recommend more detailed site-level analyses using high resolution digital elevation and land use data in order to understand the specific risks confronting any given site.

To explore which sites are most at risk to sea level rise, visit CIESIN’s map client.  For a more detailed presentation of the data, methods and results, see the Ramsar STRP Briefing Note that describes this work. Finally, statistics on the areas at risk of inundation for all coastal Ramsar sites are available for download from CIESIN.

This map and commentary is part of the Map of the Month blog series produced by the Center for International Earth Science Information Network (CIESIN). Development of this month’s blog was led by senior research associate Alex de Sherbinin and geographic information specialist Malanding Jaiteh, with senior staff associate Sandra Baptista, geographic information specialist Tricia Chai-Onn, and communications coordinator Elisabeth Sydor.

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