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GPSS-GLI Researchers study rare and real examples of low-lying islands adapting to sea-level rise

Last updated August 03, 2017

Tidal flooding in Batasan island. Credits to Ven Paolo Valenzuela



   The 5th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) projects that by the year 2100, the global mean sea-level will have risen by as much as 0.28m to 0.98m. This projection has sparked an intense debate amongst scholars and policy-makers about the possibility of climate-induced mass migration, especially in low-lying Small Island Developing States (SIDS). 


   However, due to the slow onset of sea-level rise, there is a lack of case studies that examine its actual impacts and potential adaptation strategies (currently, Atoll Island States are only experiencing complete inundation about once a year, during King tides). Furthermore, since climate projections are not yet available on the island-level, designing appropriate adaptation strategies, particularly engineering measures, is proving to be a difficult challenge. 


   To address the issue of data availability, Ma. Laurice Jamero, Dr. Motoharu Onuki, Dr. Miguel Esteban, and Ven Paolo Valenzuela of GPSS-GLI drew an analogy between climate-induced sea-level rise and earthquake-induced land subsidence in terms of their tidal flooding effects. Collaborating with researchers from Zoological Society of London-Philippines, Tokyo Institute of Technology and Ho Chi Minh City University of Technology, the group investigated the flooding experiences of four low-lying island communities in Tubigon, Bohol, Philippines that suffered from land subsidence caused by the 2013 Bohol earthquake. 


   In a study recently published by Nature Climate Change, the group examined the impacts of relative sea-level rise, and identified and evaluated various potential community-based adaptation strategies. The study provides a rare and real example of adaptation strategies against sea-level rise, and challenges the mass migration theory.


   Currently, the island communities of Tubigon become partially or completely inundated during spring tides that occur around the new and full moon phases of each month. In 2016, the islands were flooded across 44-135 days, with median flood heights reaching up to 0.2m-0.4m above ground level. Daytime flooding occurring during the southwest monsoon disrupts school activities, while nighttime flooding during the northeast monsoon increases disaster risk since it also coincides with the typhoon season.


   Despite severe flooding conditions, none of the island communities have decided to relocate to the mainland through an available government-funded project, contradicting the prevailing mass migration theory. Instead, they have mainly pursued various accommodate (i.e. in-situ) adaptation strategies that include hard infrastructures, such as building stilted housing and raising floors, and soft measures, such as elevating belongings during floods and designing taller furniture. They have also implemented “no regrets” strategies that address both flooding and their pre-existing socio-economic problems, allowing the communities to continue their daily lives on the islands. Examples include the acquisition of rainwater collectors to solve water supply issues. 


   However, not all of these strategies were effective and thus adaptive. In particular, excessive coral mining for raising floors and reclaiming land inadvertently increases the islands’ vulnerability to storm surges and decreases its sediment supply. Coral reef assessment surveys of mined areas show live coral cover of less than 10%, indicating severe degradation.


   Overall, the research highlights the need to improve our understanding of the way humans adapt to climate change, avoiding simplistic scenarios and attempting to understand how communities interact with their environment. As adaptation strategies ultimately tie back to the development agenda, such holistic ways of looking at climate change adaptation are necessary for creating more sustainable development paths for small islands communities around the planet.


A free, read-only version of the paper may be accessed here


A Japanese feature article about the paper can be read here.


An opinion article that summarizes the contribution of the paper to academic literature can be read here.


The group is also currently creating a documentary to show rare footage of extreme tidal flooding and to help the island residents of Tubigon share their story with the world. They are collaborating with Richard Crichton and John Erick Avelino of GPSS-GLI, and Christopher Chadwick of The Hatch TV in Liverpool for this project.


Indoor flooding in a house in Batasan island.
Credits to Motoharu Onuki

Coral mining.
Credits to Nicholson Tan

Primary school of Ubay during flooding.
Credits to Ma Laurice Jamero

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