Subject: GS Paper 3: Disaster Management
Context: The India Meteorological Department (IMD) recently clarified that the heavy rainfall in Assam and Nagaland did not qualify as a cloudburst, despite media reports linking it to the Upper Assam floods.
About a Cloudburst
- According to the IMD, a cloudburst is: Extremely intense rainfall of 10 cm (100 mm) or more in one hour, occurring over a localised area of about 20–30 sq. km.
- Impact: The intense rainfall exceeds the infiltration capacity of the ground, triggering flash floods, landslides, and soil erosion.
- Mini-Cloudburst: Some scientists advocate classifying rainfall of 5–10 cm in one hour over 20–30 sq. km as a mini-cloudburst.
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Mechanism of Cloudburst Formation
- Convection: Warm, moisture-laden air rises rapidly into the atmosphere.
- Orographic Lifting: Mountain ranges force moist monsoon winds to ascend, enhancing cloud formation.
- Cloud Development: Cooling and condensation produce towering cumulonimbus clouds.
- Strong Updrafts: Upward air currents suspend raindrops, allowing them to accumulate.
- Sudden Downpour: When updrafts weaken or can no longer support the water droplets, intense rainfall occurs over a small area.
Reasons for Higher Incidence of Cloudbursts in Mountainous Regions
- Orographic Effect: Mountain slopes intensify the upward movement of moist air.
- Steep Terrain: Rapid runoff increases the risk of flash floods and landslides.
- Favourable Regions: The Himalayas and Western Ghats are particularly prone to cloudbursts.
Cloudbursts in India
- Occurrence: Cloudbursts are rare but highly destructive, occurring mainly in mountainous regions.
- Climate Change: A warmer atmosphere holds more moisture, increasing the likelihood of extreme rainfall events.
- Recorded Incidents: The IMD recorded around 30 cloudbursts between 1970 and 2016, though experts believe the actual number is higher due to under-reporting.
Governance Concerns
- Misclassification: Heavy rainfall is often incorrectly labelled as a cloudburst despite not meeting IMD criteria.
- Accountability: Such misclassification may divert attention from poor land-use planning, deforestation, encroachment, inadequate drainage, and weak disaster preparedness.
Factors Making Cloudbursts Difficult to Forecast
- Localised Nature: They occur over areas smaller than the grid size of most weather models.
- Rapid Formation: They develop within a short duration, leaving little lead time.
- Mountain Terrain: Mountains obstruct radar beams, creating observation blind spots.
- Sparse Monitoring: Limited weather stations and rain gauges reduce real-time detection.
- Computational Constraints: Hyperlocal forecasting requires high-resolution models and significant computing power.
About 2026 Assam Floods
Assam is among India’s most flood-prone States due to its low-lying Brahmaputra valley, intense monsoon rainfall, high sediment load and extensive river network.
The 2026 floods have particularly affected Upper Assam, where tributaries such as the Dikhow, Disang and Dhansiri have crossed severe flood levels.
Key Factors Responsible
- Intense Rainfall and Climate Change: Heavy and concentrated monsoon rainfall causes rapid runoff and river swelling. Climate change is increasing the frequency of high-intensity rainfall events, amplifying flood risks.
- Siltation and Riverbed Rise: Rivers carry large sediment loads from the erosion-prone Himalayas and deforested slopes. Sediment deposition raises riverbeds and reduces their water-carrying capacity.
- Deforestation and Excavation: Loss of forest cover reduces infiltration and accelerates surface runoff. Excessive excavation and mining along river valleys can increase sediment flow into rivers.
- River and Drainage Constraints: The already swollen Brahmaputra can obstruct the drainage of tributaries. Embankment breaches and encroachment of wetlands further reduce natural flood-buffering capacity.
River System in Assam
- Brahmaputra System: The Brahmaputra flows through the Assam valley and receives major north-bank tributaries, including the Subansiri, Manas and Kameng, and south-bank tributaries, including the Dhansiri and Burhi Dihing.
- Barak System: The Barak River drains southern Assam and later bifurcates into the Surma and Kushiyara rivers. Important tributaries include the Jiri, Dhaleswari and Longai.
- Key Significance: Assam’s interconnected river systems, high sediment load and monsoon variability make the State highly vulnerable to recurrent floods, erosion and riverbank instability.
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Government Initiatives
- Nowcasting: The IMD is strengthening nowcasting to issue short-term weather alerts for localised extreme rainfall events.
- Mission Mausam: Aims to more than double India’s Doppler Weather Radar network and leverage Artificial Intelligence (AI) for improved hyperlocal weather forecasting.
31 Jul 2026
