Syllabus: GS–  I & V: Geography & Climatology

Why in the News?

The recurring floods in Assam have renewed the debate over whether the State’s worsening disaster risk is driven only by natural rainfall variability or is being amplified by climate change and human-induced environmental degradation such as deforestation, hill cutting and mining.

More About the News

• The work of eminent Assamese climate scientist Dr Bhupendra Nath Goswami is particularly relevant to this debate because his research has helped explain Indian monsoon variability, extreme rainfall and climate processes. 
• ‘His 1999 research contributed to the identification of the Indian Ocean Dipole, while his 2006 study demonstrated an increasing trend in extreme rainfall events over India despite relatively stable seasonal rainfall.

How Is Climate Change Changing the Flood Question?

A crucial lesson from climate science is that the total amount of rainfall is not the only thing that matters. The timing, intensity and distribution of rainfall can be equally important.

• A 2006 study led by Dr Goswami found that extreme rainfall events were becoming more frequent and intense, while moderate rainfall events were declining over central India during the monsoon period. 
  • The seasonal average could therefore remain relatively stable even as flood-producing rainfall became more dangerous.
• A warmer atmosphere can hold more moisture, creating conditions favourable for short-duration, high-intensity rainfall.
• For Assam, such intense rainfall becomes particularly dangerous because the State’s river systems receive water from steep Himalayan and hill catchments, where runoff can reach the plains rapidly.

Therefore, “normal seasonal rainfall” does not necessarily mean normal flood risk.

The Indian Ocean Dipole and Monsoon Variability

The 1999 Nature paper identified a dipole mode in the tropical Indian Ocean, now known as the Indian Ocean Dipole. It showed that differences in sea-surface temperatures between the western and eastern Indian Ocean are associated with changes in winds and precipitation and can influence climate independently of the El Niño–Southern Oscillation.

What is the Indian Ocean Dipole?

The Indian Ocean Dipole refers to an irregular difference in sea-surface temperature between the western and eastern tropical Indian Ocean.

• A positive phase generally involves relatively warmer waters in the western Indian Ocean and cooler waters near the eastern Indian Ocean.
• A negative phase represents the opposite pattern.
• These temperature differences influence atmospheric circulation and rainfall patterns.

A New Understanding of Northeast India’s Monsoon

Recent research involving Dr Goswami has also questioned the conventional understanding of the timing of monsoon onset over Northeast India.

A 2024 study in the Quarterly Journal of the Royal Meteorological Society found that the climatological onset of the monsoon over Northeast India occurs around 18 May, rather than the traditionally used early-June date, with withdrawal around 14 October. It therefore suggests a rainy season of roughly 150 days. 

This has an important policy implication: climate studies and disaster preparedness for Northeast India should account for its distinctive regional climate rather than simply applying an all-India monsoon template.

Climate Change Plus Environmental Degradation Leads to Higher Vulnerability

Climate change alone does not explain every flood. Hazard becomes a disaster when environmental and social vulnerability increase.

In Assam, several factors can work together:

• Deforestation reduces the ability of landscapes to intercept and retain rainfall.
• Hill cutting and unplanned construction can destabilise slopes and increase landslide and runoff risks.
• Mining and quarrying can disturb fragile hill ecosystems and drainage systems.
• Wetland and floodplain encroachment reduces natural spaces available to temporarily store floodwater.
• Sedimentation can reduce the carrying capacity of river channels.

Thus, the correct approach is not to ask whether floods are caused by climate change OR human activity. In many cases, the more useful question is how climatic hazards and human-induced vulnerability interact.

Why Assam Needs Region-Specific Climate Research

Assam and the wider Northeast have distinctive geographical characteristics involving the Brahmaputra-Barak river systems, Himalayan and hill catchments, high rainfall, fragile geology and transboundary rivers.

Therefore, Assam needs scientific institutions and systems capable of:

• Developing high-resolution climate and flood projections specifically for the Northeast.
• Improving extreme rainfall and flash-flood forecasting.
• Integrating rainfall, river levels, soil moisture, landslide susceptibility and land-use data into disaster planning.
• Developing river-basin-specific adaptation strategies rather than relying on one uniform flood-control model.
• Translating climate research into district-level early warnings and local disaster preparedness.

The Assam State Action Plan on Climate Change 2021–2030 provides an important policy framework for climate adaptation and resilience in the State. 

From Flood Control to Climate Resilience

The traditional approach has often focused on embankments, drainage and post-flood relief. These remain important, but climate variability requires a broader strategy.

What should Assam do?

• Strengthen observation: Expand weather radar, automatic rain gauges, river gauges and satellite-based monitoring.
• Improve early warning: Warnings should translate into village-level evacuation and preparedness rather than merely forecasting rainfall.
• Restore ecosystems: Protect forests, wetlands, floodplains and natural drainage systems.
• Adopt basin-level planning: Flood management should consider the entire river system, including upstream hill catchments.
• Climate-proof infrastructure: Roads, bridges, settlements and public facilities should be designed using future climate and flood-risk projections.
• Invest in scientific research: A dedicated regional climate research and decision-support ecosystem can help bridge the gap between scientific knowledge and public policy.

Key Takeaways 

• Flood risk depends on rainfall intensity and distribution, not merely seasonal rainfall totals.
• Dr Bhupendra Nath Goswami contributed to landmark research on the Indian Ocean Dipole and extreme rainfall. 
• The 2006 research showed that extreme rainfall can increase even when seasonal mean rainfall does not show a significant trend. 
• Recent research suggests that Northeast India’s monsoon onset may occur much earlier than traditionally recognised. 
• Assam’s flood vulnerability is the result of an interaction between climate hazards, fragile geography and human-induced environmental degradation.
• The policy response should shift from post-disaster relief to anticipation, adaptation and climate resilience.

Exam Hook: Mains Question

“Assam’s recurring floods are the result of an interaction between climate variability, environmental degradation and geographical vulnerability.” Discuss with suitable examples. (150 words)

One-Line Wrap

For Assam, the future of flood management lies not in predicting rainfall alone, but in understanding how a changing climate interacts with the State’s unique landscape and human vulnerability.