This article explores how twin cyclonic storms—Ditwah over Sri Lanka and Senyar over parts of Southeast Asia—triggered catastrophic flooding and landslides in late November 2025. Drawing on current climate science, it unpacks the complex interplay between extreme rainfall, ocean warming, large-scale climate patterns such as La Niña and the Indian Ocean Dipole, and human factors like urbanization and infrastructure gaps that turned powerful storms into humanitarian disasters.
The Twin Storms That Transformed a Season into a Disaster
In late November 2025, Cyclonic Storm Ditwah struck Sri Lanka, while Cyclonic Storm Senyar drenched Indonesia, Malaysia, and southern Thailand. These were not the strongest storms on record in terms of wind, yet they produced some of the most devastating flood impacts seen in the region since the early 2000s.
For Sri Lanka, Ditwah brought relentless, concentrated rainfall that triggered widespread flooding and landslides. At the same time, Senyar delivered days of heavy rain across the maritime continent, saturating soils and overwhelming river systems over a vast area.
Human Toll and Infrastructure Damage
The human and material losses were staggering. In Sri Lanka alone, official figures indicate:
Access to clean, safe water rapidly became a critical challenge, amplifying risks of waterborne disease and complicating recovery efforts.
In Indonesia, the toll was similarly severe, with nearly 600 fatalities and around 600,000 people displaced as floodwaters inundated homes, farmlands, and vital transportation corridors.
Why Rain, Not Wind, Drove the Catastrophe
Unlike many historic cyclones where wind damage dominates, the 2025 events were driven primarily by extreme rainfall. Both Ditwah and Senyar produced prolonged, intense downpours over heavily populated, vulnerable regions.
From a hazard perspective, these storms exemplify how rainfall extremes—rather than maximum wind speed—often dictate the scale of disaster, especially in densely settled river basins and urbanized coastlines.
How Rare Were These Rainfall Extremes?
Analysis of rainfall records suggests that the most intense downpours associated with these storms correspond to 1‑in‑30 to 1‑in‑70‑year events under today’s climate conditions. In other words, they are rare but not unprecedented—and climate warming is making such extremes more likely and more intense.
The Climate Drivers: La Niña, Indian Ocean Dipole, and Warming Seas
To understand why rainfall was so extreme, we have to consider both natural climate variability and human‑driven warming. In 2025, the climate system was strongly influenced by La Niña and a negative Indian Ocean Dipole (IOD), both of which tend to enhance rainfall over parts of the Indian Ocean and Southeast Asia.
These patterns modulate where and when storms form, and how much moisture they can carry.
Quantifying the Role of La Niña and the Negative IOD
Scientists estimate that the combination of La Niña and a negative IOD contributed around 5% to 13% of the rainfall intensity seen during Ditwah and Senyar. While that might sound modest, a 10% increase in daily rainfall can translate into significantly higher peak river flows and flood depths, especially in already saturated catchments.
Warmer Seas as a Fuel Source for Extreme Rain
Sea surface temperatures in the North Indian Ocean were about 0.2°C above the 1991–2020 average during the storms. Even such seemingly small anomalies matter: warmer oceans evaporate more water, loading the atmosphere with moisture that later falls as heavy rain.
On top of this, global warming has already pushed average temperatures roughly 1.3°C above pre‑industrial levels. Observational data show that this background warming is associated with a clear intensification of heavy rainfall:
These are not subtle changes—they represent a fundamental shift in the hydrological regime, with direct implications for flood risk, infrastructure design, and disaster planning.
Limits of Climate Models and the Challenge of Attribution
Despite robust observational evidence of intensifying rainfall, climate models still struggle to reproduce the full magnitude of these trends in Sri Lanka and the surrounding region. They also have difficulty simulating the detailed interplay between La Niña, the Indian Ocean Dipole, and local extreme rainfall.
This means that while we can confidently state that warming increases the potential for heavy rainfall, precise attribution—how much of a particular event is due to human‑caused climate change versus natural variability—remains uncertain.
Human Factors: Why the Impacts Were So Severe
Physical climate drivers set the stage, but human decisions determine how severe the consequences will be. The 2025 storms exposed multiple vulnerabilities that turned a natural hazard into a cascading disaster.
Urbanization, Exposure, and Infrastructure Gaps
Several factors amplified the impacts:
Vulnerable communities—those with fewer resources, precarious housing, and limited access to services—were disproportionately affected. This pattern is consistent with disasters worldwide: the same rainfall does not affect all groups equally.
Toward Climate‑Resilient Futures
The dual tragedies of Cyclonic Storms Ditwah and Senyar highlight an urgent reality: as the climate warms, extreme rainfall will increasingly test the limits of our infrastructure, planning, and governance.
Reducing future risk requires integrating high‑resolution climate science with urban planning, nature‑based flood management, robust early warning systems, and strong social safety nets.
We cannot prevent storms from forming.
Investing in climate resilience today is a prerequisite for safeguarding lives and livelihoods in a rapidly warming world.
Here is the source article for this story: Increasing heavy rainfall and extreme flood heights in a warming climate threaten densely populated regions across Sri Lanka and the Malacca Strait