10:45 AM - 11:00 AM
[HCG26-01] Enhancing resilience of atoll islands against sea level rise
★Invited Papers
Keywords:atoll islands, sea level rise, resilience, Tuvalu
In the course of global warming, the sea level is projected to rise by 0.3 to 1.1 meters in this century, and by more than 5 meters in three centuries in the worst-case scenario. Atolls consist of low-lying land with an elevation of 1 to 4 meters, and are under threat of being submerged by rising sea levels. There are about 500 atolls globally, and about 400 of them are distributed in the Pacific Ocean. Tuvalu, Kiribati, and the Republic of the Marshall Islands in the Pacific Ocean, and the Maldives in the Indian Ocean are all atolls. These countries are in a critical situation due to global warming caused by CO2, which they themselves emit little of. Therefore, they are appealing to the international community to join with other small island states to reduce global warming and support adaptation measures against sea level rise (Alliance of Small Island States). In response to this appeal, international support such as the Green Climate Fund (GCF) is being planned for adaptation to climate change. Atoll nations are anticipating sea walls and land reclamation as effective measures against sea level rise.
Atoll islands are formed by calcium carbonate skeletons of coral and foraminifera, which were washed up on the platform of coral reefs created by corals. The coral reefs were established 4,000 years ago, when sea level rise during the postglacial period stabilized, and atoll islands were constructed and inhabited as sea level fell by 1-2 m from 2,000 years ago (Yamaguchi et al., 2007; Kayanne et al., 2011). In atoll countries such as the Republic of the Marshall Islands and Tuvalu, the concentration of populations in the capital islands has led to the expansion of residential areas into low marshes and storm ridges, which are particularly vulnerable in atoll island landforms (Yamano et al., 2007). In addition, domestic wastewater from increasing population has created a reductive environment on the coast, degrading coral reef ecosystems and replacing coral communities with algae, thus reducing the resilience of the atoll islands against sea level rise (Fujita et al., 2013; Nakamura et al., 2020). Construction of causeways and dredge of shipping channels, piers, vertical seawalls by piling up stones also inhibit sand drift and accumulation.
The problem of atolls is not as simple as submergence by sea level rise, but a complex problem caused by the expansion of inhabitable areas into vulnerable areas, the degradation of ecosystems due to environmental deterioration, and the diminishing restoration potential of the beach due to artificial coastal structures. In order to maintain atolls against future sea level rise, global warming and sea level rise must be suppressed as much as possible, and the resilience of the land must be rehabilitated through ecosystem restoration. The restoration of ecosystems will also contribute to the improvement of the basic environment of the atoll countries. From this perspective, Tuvalu implemented a beach reclamation project on Fongafale Island in Funafuti Atoll, the capital of Tuvalu, in 2015 with the technical cooperation of JICA (Onaka et al., 2017). Beach reclamation is a practical example of green infrastructure that does not interfere with the natural sand deposition process on the island.
However, Tuvalu has since planned a large-scale land reclamation project with the support of the GCF. Tuvalu's desire for short-term, tangible measures that will lead to the expansion of its small land area is understandable. Green infrastructure as an ideal cannot be forced on them that do not yet have sufficient gray infrastructure. However, it is necessary to evaluate the stability of reclaimed land against external forces and the danger that reclamation will lead to environmental degradation in the long run, which is not sustainable and will inhibit the formation of atoll islands. The application of the best mix of green infrastructure and gray infrastructure such as seawalls and landfills, under a long-term perspective, must be based on the demands of the local government and residents, and an approach to gaining local understanding is essential for this purpose.
Atoll islands are formed by calcium carbonate skeletons of coral and foraminifera, which were washed up on the platform of coral reefs created by corals. The coral reefs were established 4,000 years ago, when sea level rise during the postglacial period stabilized, and atoll islands were constructed and inhabited as sea level fell by 1-2 m from 2,000 years ago (Yamaguchi et al., 2007; Kayanne et al., 2011). In atoll countries such as the Republic of the Marshall Islands and Tuvalu, the concentration of populations in the capital islands has led to the expansion of residential areas into low marshes and storm ridges, which are particularly vulnerable in atoll island landforms (Yamano et al., 2007). In addition, domestic wastewater from increasing population has created a reductive environment on the coast, degrading coral reef ecosystems and replacing coral communities with algae, thus reducing the resilience of the atoll islands against sea level rise (Fujita et al., 2013; Nakamura et al., 2020). Construction of causeways and dredge of shipping channels, piers, vertical seawalls by piling up stones also inhibit sand drift and accumulation.
The problem of atolls is not as simple as submergence by sea level rise, but a complex problem caused by the expansion of inhabitable areas into vulnerable areas, the degradation of ecosystems due to environmental deterioration, and the diminishing restoration potential of the beach due to artificial coastal structures. In order to maintain atolls against future sea level rise, global warming and sea level rise must be suppressed as much as possible, and the resilience of the land must be rehabilitated through ecosystem restoration. The restoration of ecosystems will also contribute to the improvement of the basic environment of the atoll countries. From this perspective, Tuvalu implemented a beach reclamation project on Fongafale Island in Funafuti Atoll, the capital of Tuvalu, in 2015 with the technical cooperation of JICA (Onaka et al., 2017). Beach reclamation is a practical example of green infrastructure that does not interfere with the natural sand deposition process on the island.
However, Tuvalu has since planned a large-scale land reclamation project with the support of the GCF. Tuvalu's desire for short-term, tangible measures that will lead to the expansion of its small land area is understandable. Green infrastructure as an ideal cannot be forced on them that do not yet have sufficient gray infrastructure. However, it is necessary to evaluate the stability of reclaimed land against external forces and the danger that reclamation will lead to environmental degradation in the long run, which is not sustainable and will inhibit the formation of atoll islands. The application of the best mix of green infrastructure and gray infrastructure such as seawalls and landfills, under a long-term perspective, must be based on the demands of the local government and residents, and an approach to gaining local understanding is essential for this purpose.