Introduction

Rising global temperatures, deforestation, and rapid urbanisation have significantly intensified the flood impacts of tropical cyclones across Sri Lanka, Malaysia, Indonesia, and Thailand. Recent cyclones such as Dithawru and Senyar produced rainfall and flooding far exceeding historical norms, marking a shift from cyclical monsoon flooding to extreme, compound climate disasters.

Why in the News

A new attribution study by the World Weather Attribution (WWA) group establishes that climate change, land-use change, and urban expansion together amplified cyclone-induced floods in Southeast Asia to unprecedented levels. Cyclone Senyar made landfall in Indonesia and Malaysia on November 26-27, while Dithawru struck Sri Lanka earlier in November, causing extensive damage and over 1,600 deaths. The study highlights rainfall intensities rising up to 160% in Sri Lanka and 50% in Malaysia compared to pre-industrial baselines, underscoring a structural climate shift rather than isolated weather anomalies.

Escalating Cyclone Rainfall in a Warming Climate

1. Global Temperature Rise: Increases atmospheric moisture-holding capacity as temperatures have risen by 1.3°C since the mid-1800s.
2. Moisture Amplification: Each 1°C rise enables the atmosphere to hold 7% more moisture, intensifying rainfall.
3. Cyclone Energy Supply: Elevated sea surface temperatures in the North Indian Ocean provided additional latent heat for cyclone formation.
4. Rainfall Extremes: Five-day rainfall events in Sri Lanka intensified by 160%, while extreme rainfall in Malaysia increased by 50%.

Sea Surface Temperature Anomalies and Storm Intensification

1. Above-Normal SSTs: Sea surface temperatures during Cyclone Senyar were 0.2°C higher than the 1991-2020 average.
2. Storm Development: Warmer oceans increased evaporation rates, strengthening storm systems and prolonging rainfall duration.
3. Frequency Shift: The study identifies a rise in extreme rainfall frequency rather than mere intensity spikes.

Deforestation as a Flood Multiplier

1. Forest Cover Decline: Sri Lanka lost 90% of forest cover between 1900 and 2020.
2. Hydrological Impact: Reduced infiltration and increased surface runoff amplified landslides and flash floods.
3. Human Impact: Rainfall-induced landslides in Sri Lanka caused over 600 deaths.
4. Indonesia Case: Nearly 25% of old-growth forests on palm oil plantations were cleared between 1991 and 2020, reducing natural flood buffers.

Rapid Urbanisation and Exposure Expansion

1. Population Exposure: Rising numbers of people reside in high-intensity flood-risk zones across Sri Lanka and Indonesia.
2. Infrastructure Stress: Roads, railways, and cropland expansion increased surface sealing and runoff velocity.
3. Flood Pathways: Inadequate drainage and altered land gradients intensified urban flooding during Cyclone Senyar.

Flood Impacts Beyond Rainfall

1. Economic Losses: Sustained economic losses estimated between $6-7 billion, equivalent to 3-5% of GDP in affected regions.
2. Agricultural Damage: More than 137,000 acres of agricultural land damaged due to floods and infrastructure failures.
3. Secondary Hazards: Flooding triggered dam breaches, canal destruction, and landslides, compounding disaster severity.

Attribution Science and Policy Significance

1. Event Attribution: Confirms climate change as a decisive factor in amplifying rainfall and flood impacts.
2. Shift in Disaster Pattern: Floods no longer limited to monsoon cycles but increasingly driven by short-duration extreme events.
3. Policy Gap: Highlights inadequate land-use planning and ecosystem protection in climate adaptation strategies.

Conclusion

The study establishes that cyclone disasters in Southeast Asia are no longer episodic weather events but outcomes of sustained climate warming, ecological degradation, and unplanned urban growth. Addressing future flood risks requires integrating climate mitigation, forest conservation, and land-use planning into disaster governance frameworks.

PYQ Relevance

[UPSC 2023] The Intergovernmental Panel on Climate Change (IPCC) has predicted a global sea level rise of about one metre by AD 2100. What would be its impact in India and the other countries in the Indian Ocean region? 

Linkage: The article reinforces IPCC projections by showing how warming oceans and climate change amplify coastal flooding risks in the Indian Ocean region. Sea-level rise acts as a risk multiplier, intensifying cyclone impacts, floods, and ecosystem loss in India and neighbouring countries.

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