El Niño and Pacific Islands: Drought, Sea Level, and Coral Reefs

Published: July 9, 2026 · 10 min read

Why the Pacific Islands Are So Sensitive to ENSO

The Pacific Ocean covers a third of the Earth's surface. Scattered across it are thousands of islands — some volcanic and mountainous, others barely rising two meters above sea level. The connection between these islands and El Niño is geographic destiny. When the Walker Circulation shifts eastward during El Niño, it rearranges where warm water sits, where clouds form, and where rain falls across the entire basin.

For a place like Tuvalu — nine coral atolls with a maximum elevation of 4.6 meters and no rivers or lakes — rainfall is the only source of freshwater beyond a thin underground lens of brackish water. The country's 11,000 residents catch rain from roofs and store it in tanks. When El Niño rearranges the rainfall map, Tuvalu's water security rearranges with it. This pattern repeats across dozens of island states: countries that contributed virtually nothing to global greenhouse gas emissions are disproportionately exposed to climate variability driven by a natural cycle they have no control over.

The statistical picture is stark. A 2015 study in Climate Dynamics found that during strong El Niño events, rainfall in the western tropical Pacific drops by 40–60% below the climatological mean, while rainfall in the central and eastern Pacific can increase by 200–300% above normal. For nations where annual GDP per capita is measured in thousands of dollars, not tens of thousands, a single extreme El Niño can wipe out years of development gains.

The East-West Divide: Who Gets Drought, Who Gets Flood

El Niño splits the Pacific Islands roughly along the 180th meridian. West of the International Date Line — Papua New Guinea, Solomon Islands, Vanuatu, Palau, and the Federated States of Micronesia — the signal is drought. East of it — Kiribati, Tuvalu, Tokelau, the northern Cook Islands, and French Polynesia — the signal is excess rainfall, sometimes to the point of flooding.

Papua New Guinea experienced this directly during the 2015–16 El Niño. Rainfall across the Highlands region fell to less than 30% of normal for five consecutive months. Frost damaged sweet potato crops at altitudes above 2,200 meters — an extraordinary event in a tropical country. The government estimated that 2.4 million people were affected by food and water shortages, with 480,000 facing critical needs. Rivers that normally supplied villages dried to trickles. Schools closed because there was no water for students to drink.

Solomon Islands saw similar conditions. The 1997–98 El Niño cut rainfall by 50–70% across most of the country. Taro — a staple root crop grown in swamps — failed across entire provinces. In the outer islands, communities resorted to drinking coconut milk as freshwater supplies ran out. The government declared a national disaster in September 1997 and had to charter ships to deliver water to isolated atolls.

On the other side of the basin, Kiribati got the mirror image. The 2015–16 El Niño brought torrential rain to Tarawa atoll, where more than half of Kiribati's 120,000 people live. The rain itself was damaging — flooding pit toilets, contaminating the freshwater lens, and triggering outbreaks of diarrheal disease. But the bigger irony is that Kiribati's "wet" El Niño years are preferable to its "dry" La Niña years, when the rain stops entirely and the shallow freshwater lens beneath each atoll shrinks toward saltwater intrusion. For Kiribati, El Niño means disease risk. La Niña means drought. Neither is good.

Coral Reefs: The Third Global Bleaching Event and Beyond

The Pacific Islands are home to roughly a quarter of the world's coral reefs. The 2015–16 El Niño triggered the third recorded global coral bleaching event — and it devastated Pacific reefs on a scale marine biologists had never documented before.

In Kiribati's Phoenix Islands Protected Area — one of the largest marine reserves on Earth at 408,000 square kilometers — surveys after the 2015–16 event found coral mortality rates exceeding 80% on some reefs. Water temperatures around the Phoenix Islands stayed above the bleaching threshold for over 10 consecutive weeks. At Kanton Island, where researchers from the New England Aquarium had monitored reefs since 2000, virtually every branching coral colony was dead.

Fiji was hit hard too. Around 50% of surveyed reefs bleached during 2016. The damage was uneven — reefs near Viti Levu's southern coast lost 30–40% of their coral cover, while some sites in the Lau group to the east saw mortality above 70%. Fiji's reefs are not just ecological assets. They underpin a tourism sector that generates roughly 40% of the country's GDP. A dead reef doesn't attract divers.

The 2023–24 fourth global bleaching event added another layer of stress to reefs that had barely begun recovering from 2016. NOAA's Coral Reef Watch recorded Degree Heating Weeks (DHW) values above 20 across large sections of the central Pacific during the 2023–24 summer — double the threshold at which significant bleaching is expected. For context, DHW of 4–8 indicates bleaching likely; above 8 means widespread bleaching and significant mortality. Values above 20 mean the water is lethally hot for reefs. I've been tracking coral data since 2015, and the 2023–24 numbers in the central Pacific were genuinely alarming — DHW accumulations that outstrip even the worst projections from a decade ago.

Sea Level: A Tilting Ocean

One of the less intuitive effects of El Niño is that it literally tilts the Pacific Ocean. During normal conditions, trade winds push warm water toward the western Pacific, creating a sea surface that is naturally about 30–40 centimeters higher in Indonesia than in Peru. El Niño weakens those trade winds, and the piled-up water in the west sloshes back eastward.

For countries in the western Pacific, this means sea level can drop by 10–30 centimeters during a strong El Niño. That might sound like a temporary reprieve, but the consequences are destructive. When sea level drops abruptly across coral atoll lagoons, the upper layers of reef flats get exposed to air at low tide. Corals that have never been exposed to air die within hours. In the 2015–16 El Niño, Marshall Islands reported widespread "reef flat emergence" — entire sections of nearshore reef were left high and dry, killing decades-old coral colonies. The Solomon Islands saw similar die-offs in 1997–98. From the deck of a boat it looks surreal: perfectly healthy reef, lifted out of the water like someone pulled a plug on the ocean.

In the eastern and central Pacific, the opposite happens. Sea level rises by 10–30 centimeters above normal as warm water floods back. For Kiribati and Tuvalu, where the average land elevation is less than 2 meters, a 20-centimeter sea level rise — even temporary — pushes storm surges over land that is normally dry. In Tarawa during the 2015–16 El Niño, king tides combined with El Niño-elevated sea levels to flood homes and contaminate well water. These aren't future climate projections; they're events that have already occurred during recent El Niño cycles.

Tuna: The Pacific's Most Valuable Moving Target

The western and central Pacific tuna fishery is the largest in the world, supplying roughly half of the global canned tuna market and generating over $7 billion annually. It is also a political keystone for the Pacific Island countries that control the waters through the Nauru Agreement (PNA) — a treaty among eight island states that collectively manage about a quarter of the world's tuna supply.

Skipjack tuna follow warm water. During El Niño, the western Pacific warm pool stretches eastward, and the skipjack follow it. In the 2015–16 El Niño, catch rates in the exclusive economic zones (EEZs) of Papua New Guinea and Solomon Islands dropped by 20–30%, while catch rates in Kiribati's EEZ — further east — increased by 15–25%. The fish didn't disappear; they moved.

This creates a revenue problem. The PNA operates a vessel day scheme (VDS) that sells fishing days to distant-water fleets, primarily from Taiwan, Japan, South Korea, and China. The price per day is based on historical catch rates in each EEZ, but those catch rates shift dramatically during El Niño. A 2018 study in Nature Sustainability calculated that the 2015–16 El Niño caused a redistribution of roughly $150 million in tuna value across Pacific EEZs. Papua New Guinea, the largest PNA member, lost an estimated $40–50 million in potential revenue during that single event. For a country with an annual government budget of roughly $4.5 billion, that is not trivial — and it lands on an economy where 85% of the population depends on subsistence agriculture.

The 2026 El Niño is expected to cause a similar eastward shift in skipjack distribution, though the magnitude depends on event strength. The PNA countries have begun discussing dynamic VDS pricing — adjusting fishing day costs based on real-time oceanographic conditions — but the system remains tied to fixed historical benchmarks.

Freshwater: When the Rain Stops on an Atoll

On a volcanic island like Viti Levu in Fiji, rivers and streams provide freshwater. On an atoll, there are no rivers. There is no groundwater in the conventional sense — just a thin freshwater lens that floats on top of denser saltwater beneath each island. This lens is replenished entirely by rainfall. During a western Pacific El Niño drought, the lens shrinks. If it shrinks enough, saltwater intrudes, and wells turn brackish. The lens doesn't recover quickly either — it can take months of normal rainfall to flush saltwater back out of the porous coral sand.

In the Marshall Islands during the 2015–16 drought, the government declared a state of emergency and began shipping reverse-osmosis water units to outer atolls. The capital, Majuro, imposed water rationing: residents were limited to 8 hours of running water per day, and hospitals stockpiled bottled supplies. Parts of the country got less rain in the first four months of 2016 than they normally receive in a single week.

Tuvalu reported that household rainwater tanks — the primary drinking water source for most families — ran dry across three of its nine atolls during the 1997–98 El Niño. The government had to charter a desalination barge from Australia. The operating cost: roughly $AUD 30,000 per day, which a country with a GDP of roughly $70 million cannot absorb for long. In 2011, when a La Niña drought hit Tuvalu (yes, Tuvalu gets drought during La Niña due to its position near the South Pacific Convergence Zone shift), the same thing happened, and New Zealand and Australia again flew in emergency desalination units. The pattern is well established now: Pacific drought triggers emergency water imports, external donors cover the cost, and the underlying water-security vulnerability remains unchanged.

Historical El Niño Impacts on Pacific Island Nations

What the 2026 El Niño Means for Pacific Islands

Based on the May 2026 NOAA forecast, the developing El Niño is tracking toward a moderate-to-strong event with an ONI peak projected between +1.5°C and +2.0°C. For the Pacific Islands, here is what that translates to:

Papua New Guinea and Solomon Islands should brace for below-normal rainfall from July through November 2026. The PNG National Weather Service has already issued drought advisories for the Highlands and Momase regions. Rice and sweet potato yields are likely to decline. Given that the country is still recovering from the 2024 floods in the Sepik region, food stocks are lower than ideal going into a drought.

Kiribati and Tuvalu can expect above-normal rainfall, which brings a mixed picture: reduced drought stress but elevated risk of waterborne disease outbreaks from flooded sanitation infrastructure. Sea level in the central Pacific is already running 5–10 centimeters above the long-term average due to background ocean warming. The El Niño pulse could push it another 15–20 centimeters higher, putting low-lying atoll communities at direct risk from high-tide flooding through early 2027.

Fiji, Vanuatu, and New Caledonia sit in a transitional zone that is harder to forecast. The 2026 event is currently projected as a basin-wide (eastern Pacific) El Niño rather than a Modoki (central Pacific) pattern, which tends to produce stronger drought signals in the southwest Pacific. Fiji's sugar industry — already shrinking — faces another season of below-normal rainfall in the western cane-growing districts around Lautoka and Ba.

Coral bleaching outlook: NOAA's Coral Reef Watch is projecting Alert Level 2 conditions (widespread bleaching and significant mortality) for the central equatorial Pacific by December 2026 if the El Niño continues strengthening. Reefs in the Line Islands, Phoenix Islands, and northern Cook Islands face the highest risk. For reefs that experienced 80% mortality in 2015–16 and then got hit again in 2023–24, a third thermal shock in a decade could push some sites into functional collapse — where coral cover falls below the level needed for the reef to maintain its three-dimensional structure.

Tuna outlook: The fisheries models run by the Pacific Community (SPC) suggest a 15–25% eastward redistribution of skipjack biomass during a +1.5°C to +2.0°C El Niño. For PNA countries in the west, this means reduced revenue from vessel day sales; for Kiribati and the eastern island states, it means a temporary windfall. The long-term concern is less about any single El Niño and more about what happens if the frequency of strong El Niño events increases. If tuna fleets start treating the western Pacific as an intermittent fishery rather than a reliable one, the economic foundation of the VDS system cracks.

For daily monitoring of ENSO conditions relevant to the Pacific, check our Real-Time Data page.

Economic & Agricultural Impacts in Pacific Islands

El Niño doesn't just change the weather — it reshapes entire economies. In Pacific Islands, the agricultural sector is often the first to feel the impact. When rainfall patterns shift, crop yields follow. When temperatures spike, livestock suffer. The ripple effects move through supply chains, commodity prices, and eventually household budgets.

For 2026-2027, key economic vulnerabilities include:

• Agriculture: Reduced rainfall during critical growing seasons can cut crop yields 10-30%. Farmers face difficult decisions about planting windows and crop selection.
• Water resources: Reservoir levels and groundwater recharge rates decline during El Niño droughts, affecting both irrigation and municipal water supplies.
• Energy demand: Higher temperatures drive up cooling demand. In regions dependent on hydropower, reduced rainfall creates a double squeeze — more demand, less supply.
• Insurance & disaster costs: El Niño-correlated extreme events (drought, flood, fire) increase claims and strain public disaster budgets.

The World Bank estimates that a strong El Niño can reduce GDP growth in vulnerable regions by 0.5-2.5 percentage points, primarily through agricultural losses and disaster response costs. For Pacific Islands, preparedness investments made now — drought-resistant crops, water storage, early warning systems — pay for themselves many times over during the event.