In the summer of 2022, 20 islands in the Maldives were flooded when a distant swell event in the Indian Ocean coincided with an extremely high tide level.
A new and detailed analysis of that incident, compiled using fieldwork and computer modelling, has shown it to be a relatively rare occurrence with the worst flooding seen in the region since the Boxing Day tsunami of 2004.
However, scientists have warned that future predicted rises in sea levels, potentially coupled with an increase in extreme weather events and wave conditions, could result in such flooding becoming far more common, perhaps happening every two to three years by around 2050.
It has led them to call on authorities in the Maldives, and other low-lying island nations, to urgently identify, evaluate and implement adaptation strategies to mitigate against the adverse impacts of flooding without delay.
The research, published in the journal Coastal Futures, was carried out by researchers from the University of Plymouth and Deltares, a not-for-profit applied research institute in the Netherlands, as part of the ARISE project, a £2.8million programme supported by UK Research and Innovation.
Professor Gerd Masselink, Professor of Coastal Geomorphology at the University of Plymouth and leader of the ARISE project, said: "Low-lying atoll islands are among the most vulnerable places on Earth due to rising sea levels and, when they flood, it is disruptive and potentially hazardous. Global computer modelling studies suggest that by 2050 what used to be rare, extreme floods – like those experienced in the Maldives in 2022 – could happen every year in tropical regions. However, our research has also shown how waves washing over an island can deposit coral sand and rubble onto the island's surface, raising its elevation and potentially making it more resilient to future flooding events and sea-level rise. It is a complex picture and, for people living in these communities and the infrastructure protecting them, is an area that needs to be studied further."
The study is the latest led by scientists in Plymouth to explore the effect of rising sea levels and other climate related events on atoll nations in the Indian Ocean and the Pacific Ocean.
Previous research has suggested that despite the nations being extremely vulnerable to the effects of climate change, island 'drowning' might not be inevitable as atoll islands without significant coastal protection structures, such as seawalls, could naturally adapt and survive.
Building on that, this research simulated the July 2022 flooding event through XBeach, a coastal flooding and erosion computer model, developed at Deltares in collaboration with international partners including the University of Plymouth.
The computer model results were compared with field observations made in January and July 2022 on the island of Fiyoaree, at the south west tip of the Huvadhoo Atoll.
The model was reasonably accurate in predicting the height the waves reached, and the extent to which flooding spread across the island, with the researchers believing the results would likely be replicated across other Maldivian islands with similar physical characteristics.
They ran their model for all 158 storm events that occurred over the period from 1990 to 2023. Only one of these storms – the July 2022 event – resulted in predicted flooding with current sea level, but an additional nine of these historic storms would result in predicted flooding by 2050 due to the additional sea-level rise.
While the model did not factor in natural or anthropogenic adjustments over the next quarter of a century, the results prompted the scientists to forecast that while significant island flooding only occurs every 25 years at present, such events could occur every few years by 2050.
Dr Robert McCall, a coastal flooding specialist at Deltares and one of the co-authors of the study, said: "Low-lying atoll island nations are clearly going to face increasing risk of coastal flooding as sea levels rise. Research such as this allows us to support governments and other decision-makers to plan for the future, by quantifying when, where, and by how much, the risk of flooding will increase. Importantly, we can also use our understanding of the processes leading to flooding to support the selection and design of flood protection, mitigation, and adaptation solutions, helping societies to manage future flood risk."
* The Natural adaptation of atoll islands to sea-level rise offering opportunities for ongoing human occupation (ARISE) project aims to revolutionise our capability to model the physical impacts of sea-level rise on atoll islands. A five-year £2.8million project, it is led by the University of Plymouth and funded by the Engineering and Physical Sciences Research Council, part of UK Research and Innovation.
