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While the prioritisation of scarce resources for climate adaptation is becoming a priority for low and middle income countries, the climate service literature addressing adaptation prioritisation decisions is scarce. This paper contributes to filling this gap by presenting a co-creation process carried out in the Maldives among representatives of government, civil society and researchers. Together, we identified the need to improve a ranking method currently used by the Maldivian government to prioritise islands for investments in erosion prevention. As a solution we developed a layered index. The first layer of this index captures the objective dimension of the problem through an erosion hazard subindex, using the three variables wave energy, reef health and reef flat minimum width. The second layer captures the normative dimension through a multi-criteria analysis using the erosion hazard subindex as one criterion next to other stakeholder selected criteria such as critical infrastructure, economic activity, per capita income and the potential to house additional people that resettle from riskier places as sea-level rise progresses. Results of this new ranking method show that socioeconomic criteria were considered more important by the stakeholders than the biophysical criterion of erosion hazard. Among the top-ranked islands are many regional centres but also less populous islands that have a large potential to house additional people. Lessons learnt from the co-creation process highlight the importance of assembling interdisciplinarity teams, fostering mutual learning among project participants, and designing research projects that do not prescribe upfront the exact problems to be addressed and methods to be applied.

Low-lying atoll nations (e.g. the Maldives, Kiribati, Tuvalu, Marshall Islands) are highly vulnerable to climate change, especially sea-level rise (SLR). Stringent climate change mitigation will slow but not stop SLR, which will continue for centuries, mandating additional long-term adaptation. At the same time, urbanisation is concentrating population in a few centres, especially around capital islands which creates additional pressure as most atoll nations are ‘land-poor’. This paper demonstrates how structural adaptation using land claim and island raising can be utilised within an adaptation pathway approach to sustain enough islands and land area above rising sea levels to satisfy societal and economic needs over multiple centuries. This approach is illustrated using the Maldives, especially around the capital and its environs (Greater Malé). Raising, expanding and connecting ‘urban’ islands can provide multiple benefits. Significant developments have already occurred in Greater Malé and further developments there and for other urban centres in the Maldives are expected. Migration to urban centres, especially Malé, is widespread and this adaptation approach assumes this trend continues, implying many other islands are depopulated or abandoned. Tourism is core to the Maldives economy and tourist islands require a different ambience to urban islands. They could be sustained with sympathetic soft engineering reinforcing the natural processes that produce atolls. While land advance and island raising provides a technical solution for SLR, any application must also address the additional policy, human, physical, engineering and economic/financial challenges that are raised. Nonetheless, by aligning adaptation through land advance/raising with existing development trends, atoll nations have the potential to persist and prosper for many centuries even as sea levels inevitably rise. This provides a realistic alternative to widespread assumptions about forced migration and ultimate national abandonment. The lessons here may find wider application to other small island settings and even mainland coasts.

The Maldives, with one of the lowest average land elevations above present-day mean sea level, is among the world regions that will be the most impacted by mean sea-level rise and marine extreme events induced by climate change. Yet, the lack of regional and local information on marine drivers is a major drawback that coastal decision-makers face to anticipate the impacts of climate change along the Maldivian coastlines. In this study we focus on wind-waves, the main driver of extremes causing coastal flooding in the region. We dynamically downscale large-scale fields from global wave models, providing a valuable source of climate information along the coastlines with spatial resolution down to 500 m. This dataset serves to characterise the wave climate around the Maldives, with applications in regional development and land reclamation, and is also an essential input for local flood hazard modelling. We illustrate this with a case study of HA Hoarafushi, an atoll island where local topo-bathymetry is available. This island is exposed to the highest incoming waves in the archipelago and recently saw development of an airport island on its reef via land reclamation. Regional waves are propagated toward the shoreline using a phase-resolving model and coastal inundation is simulated under different mean sea-level rise conditions of up to 1 m above present-day mean sea level. The results are represented as risk maps with different hazard levels gathering inundation depth and speed, providing a clear evidence of the impacts of the sea level rise combined with extreme wave events.

Abstract The Maldives (land elevation approximately 1 m above mean sea level) is often associated with the threat of rising sea levels. Land scarcity due to population pressure is also a major issue. In the late 1990s a new 1.9km2 1.8 m high artificial island, Hulhumalé was created for urban expansion, including an allowance for sea‐level rise. This paper assesses flood exposure through an extreme water level scenario on Hulhumalé taking into account sea‐level rise and analyses potential adaptation options to extend island life. Results indicate that overtopping is likely to occur with 0.6 ± 0.2 m of sea‐level rise, with more severe, widespread flooding with 0.9 ± 0.2 m of sea‐level rise. If the Paris Agreement goals are met, flooding is not anticipated this century. However, under a non‐mitigation scenario, flooding could occur by the 2090s. Building seawalls 0.5, 1.0, and 1.5 m high could delay flooding for 0.2, 0.4, and 0.6 m of sea‐level rise, respectively. Land raising has been successful in Hulhumalé in reducing flood risk simultaneous to addressing development needs. Whilst new land claim and raising can be cost‐effective, raising developed land provides greater challenges, such as timeliness with respect to infrastructure design lives or financial costs. Thus the transferability and long‐term benefits of land raising requires further consideration.