A strong El Niño is underway and is strengthening in the Pacific while a positive Indian Ocean Dipole (IOD) is expected to develop. Both events are known to alter sea temperatures, rainfall and water levels, creating conditions that place mangroves under severe stress.
Against the backdrop of a changing climate, these events can amplify local environmental conditions in ways that are difficult to detect until impacts become visible. Recognising these signals early, through strengthened monitoring and early warning systems to detect changes in sea level, salinity and ecosystem health, can help governments and coastal communities anticipate risks and take informed actions.
Mangroves are a vital part of coastal ecosystems, helping protect shorelines from erosion and storm impacts, providing habitat for fish and other wildlife, storing large amounts of carbon, and supporting livelihoods, food security and cultural traditions. Asia and the Pacific account for more than half of the world’s mangrove share, making their resilience critical not only for biodiversity but also for the millions of people who depend on them.
The IOD and El Niño are large-scale climate patterns that influence ocean temperatures, rainfall and sea levels across the Indo-Pacific region. They can create prolonged flooding, unusual heat and elevated salinity in coastal wetlands, placing significant stress on mangrove ecosystems, sometimes across multiple countries simultaneously. Acting independently or interacting, these two events have significant effects on ocean and coastal life. Understanding how they influence these local conditions is therefore essential to protecting mangroves and strengthening the resilience of coastal communities.
Due to a positive IOD in 2020–2021, the Maldives experienced one of the most significant recorded mangrove dieback events in its history, with impacts reported on roughly one-quarter of the country’s mangrove-bearing islands and losses exceeding 40 per cent of mangrove cover in some locations. These were driven by raised sea levels, leaving many mangrove wetlands flooded for extended periods.
In low-lying mangrove systems with poor drainage, seawater became trapped, evaporation concentrated salt in the soil, and tree roots were deprived of oxygen. This combination of flooding, heat stress and salt accumulation weakened and killed large numbers of mangroves.
Sharing the same vulnerabilities, this positive IOD triggered widespread mangrove losses across the Western Indian Ocean, striking as far as the Seychelles, Comoros, Mayotte and Madagascar. Studies from other regions, including northern Australia during the 2015–2016 El Niño, have similarly linked these climate oscillations to large-scale mangrove dieback, demonstrating how such events can push already-stressed coastal ecosystems beyond their natural tolerance limits.
When a strong positive IOD occurs alongside El Niño, the combined effects have historically been associated with higher sea temperatures and sea levels, changes in rainfall, prolonged flooding in some areas and increased salinity in coastal wetlands. Many mangrove ecosystems are resilient and can recover from periodic climate fluctuations, but they have limits. Monitoring these large-scale climate patterns can provide valuable early warning and help coastal managers respond before ecological stress becomes widespread.
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