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Context
Cloudbursts in India are relatively rare, highly localized extreme weather events defined by the India Meteorological Department (IMD) as receiving 100 mm or more of rainfall within one hour over a geographical area of 20–30 square kilometers. While infrequent compared to standard monsoon downpours, their frequency and intensity are surging across the Himalayan and sub-Himalayan states.
Introduction and Definition
- IMD Definition: According to the India Meteorological Department, a cloudburst is an excess of rain beyond 100 mm/h over a small area of about 20 to 30 km² over a short period of time.
- Distinction: Not every spell of heavy or extreme rain qualifies as a cloudburst. It is an extreme convective event which involves a large amount of water falling in a short period of time.
How common are they in India?
- Historical Statistics: Official statistics indicate that the occurrences are rare. Information provided in the Parliament showed that there were close to 30 cloudbursts reported in the IMD between 1970 and 2016.
- The Monitoring Gap: Experts believe that these are underestimates. Cloudbursts are mainly in the remote high ranges of the Himalaya where the density of weather stations as well as rain gauges is very low. It’s possible for an event that is just a few kilometers away from a manual or digital gauge to go unrecorded, even though it causes catastrophic downstream flash flood downstream.
- Geographical Concentration: These are frequently observed over the northwestern and western Himalayan states (Himachal Pradesh, Uttarakhand, Jammu & Kashmir and Ladakh), and sometimes the Northeastern hills, during July–August when moisture-laden monsoon currents meet steep slopes.
Mechanism of Occurrence
- Orographic Lift: When the warm and moist easterly winds with origin on the Arabian Sea or Bay of Bengal rise against the high mountains and cool rapidly, they condense into heavy towering Cbs.
- Upward Air Currents (Updrafts): Strong vertical air currents of hot air rise from the hot valley bottoms, which lift the rain drops and cause them to fuse and merge together through the Langmuir precipitation process.
- The Sudden Burst: When the thermal updrafts weaken or can no longer hold up the mass of water, gravity kicks in and the water that’s built up pours off over a small area in a flash.
Climate change and anthropogenic triggers.
- Atmospheric Warming: A warmer atmosphere can contain about 7% more moisture for every 1°C of temperature increase, providing fuel for more intense convective storms.
- Land-Use Changes: Uncontrolled infrastructure development, unscientific cutting of hill slopes for all-weather roads, deforestation and heavy tourist traffic in fragile ecologies lead to worsening micro-climatic instability and reduce the water retention capacity of the land.
- The Accountability Debate: Environmentalists say that local governments frequently give this “cloudburst” term to try to shift responsibility away from structural failures and man-made construction on riverbanks.
Disaster Management and Way Forward
- Early Warning Limitations: Cloudbursts are a challenging meteorological phenomenon to predict hours ahead because of their small scale and rapid timing. Weather radars (doppler) are very important if they can be deployed in the high-risk valleys in the Himalayas.
- Mitigation Strategies: The National Disaster Management Authority (NDMA) guidelines mandate strict zoning regulations, banning construction in the first and second order stream paths, mapping debris-flow risks, and introducing community level real-time rain sensors.
Source: The Hindu
UPSC Mains Practice Question
Q. Cloudbursts are emerging as one of India’s most destructive extreme weather events. Examine the causes, impacts, and suggest measures to improve forecasting, preparedness, and disaster resilience.
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