On the morning of 4 August 2026, residents of Nawalapitiya in Kandy District walked across a road buried in mud. Two days of downpours had sent hillsides sliding onto houses in Sri Lanka’s central tea country. The Disaster Management Centre reported that five people died when mudslides overran two homes, two more were killed by floodwater, 129 houses were damaged and about 3,500 people had to leave their homes.

It was not a large disaster by Sri Lankan standards. That is precisely what makes it alarming. It struck the same hills that Cyclone Ditwah had torn open eight months earlier, when landslides and floods killed about 640 people and caused an estimated $4.1 billion in damage. Roads, railways and houses there are still being rebuilt. The slopes have not healed.

Now a far larger threat is building thousands of kilometres away. In the central Pacific, El Niño has strengthened into what forecasters expect to be one of the most powerful events on record. In the Indian Ocean, a positive dipole is forming alongside it. Decades of research link this pairing to heavier rain over Sri Lanka in October and November, the same months that produced most of the country’s recent flood deaths.

To understand what this could mean, we compiled every Disaster Management Centre figure we could verify for floods between 2021 and 2025, mapped which districts were hit and when, and set that record against the latest seasonal forecasts. The pattern is consistent, and it points in one direction.

A disaster every year, and one that broke the scale

Floods are not an occasional emergency in Sri Lanka. A 2026 review published on ScienceDirect notes that the country has recorded flood-related damage every year for four decades, and that most of its people and economic activity sit in low-lying areas prone to flooding.

The five-year record makes that concrete. In 2021, three separate waves of flooding killed at least 47 people and affected more than half a million. In 2023, three episodes between October and January killed at least 28 and affected close to 300,000. In 2024, four distinct flood events affected more than 800,000 people. Then came Ditwah.

Ditwah was not a powerful storm by wind speed. What made it catastrophic was rain that would not stop. It lingered over the island for nearly three days. One station in Matale District recorded 540.6 millimetres, which the head of the Department of Meteorology described as possibly the highest in the country’s recent history. By mid-December, the DMC had counted 643 deaths, 183 people missing and around 2.3 million people affected, about a tenth of the population.

The scale of the damage exposed how much of the country depends on fragile systems. At one point, only 478 of 1,593 kilometres of railway remained usable, and water treatment plants in Kandy and Ambatale were submerged or shut.

The calendar of danger

When we plotted every major flood event by month, a clear shape emerged. Sri Lanka’s southwest monsoon, from May to September, reliably floods the western and southern lowlands. But the deadliest events cluster in the last quarter of the year, during the second inter-monsoon period and the start of the northeast monsoon, when low-pressure systems and cyclones from the Bay of Bengal can stall over the island.

November was the deadliest month of the year in 2021, 2023 and 2025, and in 2024 it brought the flood that reached the most people. The late-year disasters of 2021, 2024 and 2025 were all driven by low-pressure systems or cyclones from the Bay of Bengal. This matters for planning: the months ahead are not a quiet stretch after the monsoon. They are the peak.

In three of the last five years, November was the deadliest month for floods.

Two kinds of risk, two different maps

Asking which districts are “worst hit” by floods produces two very different answers depending on what is being counted.

If the measure is people affected, the answer is the densely populated western lowlands. During Ditwah, the largest affected populations were in Gampaha, Puttalam and Colombo, each above 320,000 people. These districts sit on the floodplains of the Kelani, Attanagalu and Kalu rivers, where urban growth, land reclamation and blocked drains make floods worse.

If the measure is lives lost, the answer is the central highlands. There, sustained rain saturates steep slopes until they fail, burying houses. The Copernicus emergency flood service found that the highest casualty rates during Ditwah were among estate-sector workers living in slope-side housing.

That split has direct consequences for policy. Flood warnings, boats and river gauges protect people in Gampaha and Colombo. On a hillside in Kandy or Badulla, the danger is not rising water but a slope above the house. A warning that says “flood” does not tell a family in a line house on a tea estate that it needs to leave tonight.

The same districts, year after year

We then recorded which districts were named among the worst affected in each major event. The recurrence is striking. The same river basins and the same hills appear again and again.

Gampaha appears in four of the five full years. Ratnapura, Kandy and Nuwara Eliya appear in four. The eastern districts of Ampara and Batticaloa surface whenever the northeast monsoon turns heavy. None of this is surprising to disaster officials. What the matrix shows is that risk is not random, and that the places needing protection before this season are already known.

The ocean signals behind this year’s warning

Sri Lanka’s rainfall is shaped by two ocean patterns. El Niño is a warming of the central and eastern Pacific that shifts rainfall around the world. The Indian Ocean Dipole describes a temperature difference between the western and eastern Indian Ocean; in its positive phase, the west is warmer and the east cooler.

Both are now in their warm, positive phases, and both are strong.

The forecasts are unusually confident. All 22 models in the IRI forecast plume keep El Niño conditions in place into early 2027. NOAA puts the chance of a very strong event above 90 percent. WMO says El Niño is almost certain to persist through February. Sri Lanka’s Department of Meteorology has highlighted NOAA’s estimate of a 75 percent chance that the October–December event will be the strongest since 1950.

Why this means more rain for Sri Lanka

For much of South Asia, El Niño is associated with drought. Sri Lanka is different in the last quarter of the year. A landmark 2003 study by Lareef Zubair and colleagues found that the Indian Ocean Dipole significantly shapes Sri Lanka’s Maha-season rainfall, independently of El Niño. A review by India’s Meteorological Department concludes that an El Niño combined with a positive dipole is likely to boost seasonal rainfall over Sri Lanka.

The same review adds a crucial detail. During El Niño years, the extra rain shows up mainly in the second inter-monsoon period, October and November, while the northeast monsoon proper can actually be weaker. The strongest warning, in other words, is for the next eight weeks.

Sri Lanka’s own forecasters agree. In August, Director General of Meteorology Ajith Wijemanne said the department expects above-normal rain in October and November, possibly exceeding seasonal averages, with rain likely to continue into December and early January, concentrated in the Northern, Eastern and North Central provinces.

The last time this happened

The closest recent comparison is 2023, when a positive dipole also developed alongside El Niño. That year, the southwest monsoon failed and parts of the country faced drought. Then the rain arrived late and hard: floods in October, again in November, and again from December into January, killing at least 28 people and affecting close to 300,000. This year’s El Niño and dipole are both forecast to be stronger than in 2023.

Full reservoirs, early crops, damaged hills

Three local conditions make this season more dangerous than the ocean signals alone would suggest.

First, the reservoirs. National storage stood at 39 percent in August, above the 32 percent normally needed for the Maha season, and Mahaweli reservoirs were at 54 percent. That is good news for farmers but leaves less room to absorb heavy rain. During Ditwah, emergency releases from reservoirs helped flood downstream communities and wiped out stocked fish in the Eastern Province.

Second, the crops. Because of the El Niño forecast, the government moved the Maha cultivation season forward, with planting across most major irrigation schemes expected in early October. That puts young paddy in the fields during the period of highest flood risk.

Third, the hills. The August landslides showed that slopes in Nuwara Eliya and Badulla remain unstable after Ditwah. Rebuilt houses, temporary shelters and damaged roads sit on ground that has already failed once.

What the next four months could look like

No forecast can say when or where a specific storm will strike. But the combination of the five-year record, the 2023 comparison and this year’s stronger signals allows a reasonable range of outcomes. The scenarios below are our planning estimates, not official forecasts. They are meant to help authorities and communities prepare for a realistic range, not a single number.

The most likely outcome, in our assessment, is an elevated season: three or four significant flood episodes, a higher death toll than in a normal year because of fragile highland slopes, and between 400,000 and 900,000 people affected. The pivotal uncertainty is whether a depression or cyclone from the Bay of Bengal crosses or stalls over the island during peak rains. That is what made the late-year floods of 2021, 2024 and 2025 the most damaging of their seasons.

Warnings that arrive, but do not protect

The hardest lesson of the past five years is that Sri Lanka’s warning system can work on paper and still fail people. Ahead of Ditwah, the Department of Meteorology issued red alerts 72 hours before landfall and the DMC activated its emergency plan. Hundreds still died, most of them on slopes where a warning about rain did not translate into a decision to leave.

Recurrent floods also wear communities down. The humanitarian analysis group ACAPS found that repeated flooding has reduced the ability of households to cope and may have stretched the state’s capacity to help. Galle and Ratnapura, both flooded again and again, were among the districts with higher food insecurity in 2024.

This season arrives with something Ditwah did not offer: months of notice. WMO has stressed that seasonal forecasts create a window for early action. That window is now roughly three weeks wide before the October rains.

What needs to happen, and when

For government and disaster agencies

1. Before mid-October: move people off the most dangerous slopesUse NBRO landslide maps and Ditwah damage records to identify households in red zones in Kandy, Nuwara Eliya, Badulla, Matale and Kegalle, and relocate them before the rain rather than after a trigger threshold is crossed.
2. Before mid-October: agree reservoir release rulesPublish spill protocols for Mahaweli and other large reservoirs that balance the early Maha start against flood storage, and tell downstream communities in advance when and how releases will happen.
3. October: pre-position for the western and southern lowlandsStage boats, food, water purification and medical supplies in Gampaha, Colombo, Kalutara, Galle, Matara and Puttalam. Clear drains and canals, and cut back high-risk roadside trees.
4. November: prepare for a Bay of Bengal systemHave cyclone-scale plans ready nationwide, including school closure triggers, rail and road contingency plans, and protection for water treatment plants.
5. December to January: shift focus east and northMove resources to Ampara, Batticaloa, Trincomalee, Polonnaruwa and the northern districts as the northeast monsoon takes over, and launch dengue control after each flood.

Two further measures cut across the whole season. Warnings should be issued in Sinhala, Tamil and English and turned into specific instructions, such as which shelter to use and when to leave. And relief money should be released when forecasts cross agreed thresholds, not only after damage is counted.

For households

Families living on slopes should agree now on where they will go, and leave at the first signs of danger: new cracks in walls or ground, tilting trees or poles, muddy water from springs, or unusual rumbling. They should not wait for an official order. Families in flood-prone lowlands should keep documents and medicines in waterproof bags and know their evacuation route. Farmers should follow irrigation and agriculture advisories on planting and reservoir releases. No one should cross flooded roads or shelter under trees during storms, and standing water should be cleared after floods to limit dengue.

The difference a warning makes

The data in this investigation describe a country that floods every year, loses most lives on the same hillsides, and has recently suffered its worst floods in decades. They also describe a season that, unusually, can be seen coming months in advance.

Whether the coming months resemble 2023, with its several deadly but contained floods, or something closer to Ditwah will depend partly on the weather. It will also depend on decisions that can be made in the next few weeks: who is moved off unstable slopes, how reservoirs are managed, where supplies are placed, and whether warnings reach people in a form they can act on.