Impact details: landward migration

impact chain for tropical coastal areas / sea-level rise (click nodes to view details):
selected case study results:
Case study reference
Spatial context
Impact description (case study)
Case study recommendations
López-Medellín, X., Ezcurra, E., González-Abraham, C., Hak, J., Santiago, L. S., & Sickman, J. O. (2011). Oceanographic anomalies and sea-level rise drive mangroves inland in the Pacific coast of Mexico. Journal of Vegetation Science, 22(1), 143-151. Central America / Caribbean: Mexico Mangrove areas in the Pacific coast of Mexico have been increasing in the recent past due to the flooding of new areas as a consequence of sea-level rise. However, the mangrove fringe is receding as it is directly affected by sea-level rise. The inland expansion (or landward retreat) of mangroves does not ease conservation concerns, as it is the seaward fringes, and not the inland margins, that provide the most valuable ecosystem services for fisheries and coastal protection. Seaward fringes should be conserved with priority, although there is a need to better understand the balance between mangrove loss and mangrove expansion in order to foster more effective conservation activities in coastal areas.

Gilman, E., Ellison, J., & Coleman, R. (2007). Assessment of mangrove response to projected relative sea-level rise and recent historical reconstruction of shoreline position. Environmental monitoring and assessment, 124(1-3), 105-130. Pacific / Pacific Islands: American Samoa The observed mean landward migration of three mangroves' seaward margins in American Samoa over four decades was 25, 64, and 72 mm a(-1), 12 to 37 times the observed relative sea-level rise rate. Two of the sites had clear trends in reductions in mangrove area, where there was a highly significant correlation between the change in position of the seaward mangrove margin and change in relative sea-level. Here it can be inferred that the force of sea-level rise relative to the mangrove surface is causing landward migration. Shoreline movement was variable at a third site and not significantly correlated with changing sea-level, where it is likely that forces other than change in relative sea-level are predominant. Currently, 16.5%, 23.4%, and 68.0% of the three mangroves' landward margins are obstructed by coastal development which inhibits natural landward migration. The three mangrove ecosystems could experience as high as a 50.0% reduction in area by the year 2100. A 12% reduction in mangrove area by the year 2100 is possible in the Pacific islands region. Management authorities are encouraged to assess shoreline response to projected relative SLR and adopt appropriate policies to provide adequate lead time to minimise social disruption and cost, minimise losses of valued coastal habitats, and maximise available options. Use of hard engineering technology including seawalls, revetments, and bulkheads are likely to result in increased vulnerability. Rehabilitating mangroves as a means to mitigate predicted mangrove losses resulting from SLR is a no-regret option that should be pursued.

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