Incidents of mangrove dieback – plants dying from the tip downwards – during 2020 and 2021 could be attributed to climate change and rising sea levels, according to the results of a study published last week in Springer Nature, a leading peer-reviewed journal.

A combined area the size of 33 football fields completely lost its mangrove cover during the mass die-off. Nearly a million trees were estimated to have perished, mostly affecting Bruguiera Cylindrica, a mangrove plant locally known as kandoo.

The findings revealed the “extreme climate vulnerability” of island ecosystems in the Maldives, observed Aishath Farhath Ali, a wetlands and blue carbon researcher who co-authored the study.

“Climate patterns such as La Niña and Indian Ocean Dipole events, which contributed to the recent dieback, are projected to strengthen with global warming, repeating these deadly conditions,” she told the Maldives Independent.

“Globally, similar mangrove collapses (for example in Australia and Indonesia) have been linked to climate extremes. Without urgent action – like local conservation efforts, some mangrove ecosystems can face the same fate in the future.”

The first incidents of mangroves vanishing in the Maldives were reported during the dry season in March 2020 from the islands of Kelaa, Uligan, Neykurendhoo and Vaikaradhoo in the northernmost atolls. The phenomenon was later observed on at least 11 islands throughout the following year, including from islands in the southern atolls, prompting the Maldives government to invite a team of researchers from the Cochin University of Science and Technology to conduct research in December 2021.

For the first time, the study painted a clear picture of how climate change induces such events, Dr S. Bijoy Nandan, a co-author and dean of the marine sciences faculty at the Cochin University, told the Maldives Independent.

“After analysing all these samples we had collected, the main conclusion is increased salinity. There is a tremendous increase in salinity across all the sites where the die-off occurred and this especially affected Bruguiera Cylindrica, which is not very tolerant to increased salinity,” he explained.  

“In the die-off sites where massive trees of Bruguiera Cylindrica had died off in mass, we also found other species of mangroves doing well and thriving,” he noted. 

The research team identified extended drought-like conditions, sea level fluctuations, and increased salt levels in the soil as the key factors behind the widespread decline. 

Warmer temperatures, lack of rainfall and saltwater intrusion due to the rising sea level increased the salt content in the soil of the mangrove ecosystems, triggering the massive dieback, they concluded.

These conditions were worsened by triple La Niña events and the Positive Indian Ocean Dipole.

La Niña represents the cooler phase of the El Niño-Southern Oscillation cycle, marked by below-average ocean temperatures. The 2021-2023 event was highly unusual, as La Niña persisted for three consecutive years instead of the usual nine- or 12-month duration. 

The Positive Indian Ocean Dipole is a regional climate pattern that leads to warmer sea surface temperatures in the western Indian Ocean, whilst the eastern part experiences unusually cooler waters.

This dynamic significantly impacts rainfall and temperature, causing rainfall to decline and temperature to rise.

Temperatures across the Maldives have increased on average by 0.8 degrees Celsius over the past 30 years. Sea levels have shown an average increase of 3.8 to 4.6 inches compared to the 1990s, according to the Maldives Meteorological Service, For the same period, although total rainfall remained unaffected, the number of rain days decreased, while high-intensity rain days increased.

Sea levels are projected to rise between 0.15 meters and 0.31 meters by 2050. This projection is based on the “middle of the road” scenario outlined by the IPCC, in which progress towards climate action is slow and temperatures rise by 2.7 degrees Celsius by the end of the century.

The rising sea level is expected to worsen saltwater intrusion, which would ultimately affect farming, said Ahmed Shabin, the Met office climatologist.

“Even in the best-case scenario of climate action, sea levels are projected to increase across the Maldives. As a result, wave surge events are likely to be more frequent with more inland flooding. Saltwater intrusion into the freshwater lens is bound to impact agriculture as well,” he told the Maldives Independent.

The Cochin University findings echoed a study conducted by the UK’s Northumbria University, which reached the same conclusions about the mangrove dieback being driven by rising sea levels and the effects of the Indian Ocean Dipole. Similar episodes will likely become more frequent and widespread as these climate conditions intensify globally, the researchers warned.

“These findings reveal the vulnerability of mangrove ecosystems to rapid sea-level rise and highlights the urgent need for adaptive conservation strategies in Small Island Developing States,” the authors wrote in the Scientific Reports journal in 2024.