Racing the King Tide

Adaptation strategies for relative sea-level rise

A free, read-only version of a journal article containing the full details of tidal flooding and adaptation in the islands of Tubigon may be accessed here. The study was published by Nature Climate Change, and was featured on the cover of its August 2017 issue.

Rationale of the Study

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, the study drew an analogy between climate-induced sea-level rise and earthquake-induced land subsidence in terms of their tidal flooding effects. The study then examined the impacts of relative sea-level rise, and identified and evaluated various potential community-based adaptation strategies.

Key Findings

The study provides rare and real examples 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 study shows that environmental factors (i.e. frequency and height of flooding) alone do not directly lead to mass migration, refuting the assumption of the mass migration theory. It therefore highlights the need to improve our understanding of the way humans adapt to climate change, avoiding simplistic scenarios and attempting to better appreciate how communities interact with their environment. Furthermore, the experience of the islands of Tubigon emphasizes the need to identify and improve potential in-situ adaptation strategies. As adaptation strategies ultimately tie back to the development agenda, holistic ways of looking at climate change adaptation are necessary for creating more sustainable development paths for small islands communities around the planet.

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