Cyclones & Heatwaves: Atmospheric Storms

UPSC Mains PYQs

Cyclone Vulnerability & Management (2013): "India's long coastline makes it highly vulnerable to tropical cyclones." Discuss the factors responsible for the higher frequency and intensity of cyclones in the Bay of Bengal compared to the Arabian Sea. Assess the role of the National Cyclone Risk Mitigation Project (NCRMP) in cyclone disaster management. (15 Marks, 250 Words)
Heatwaves as a Disaster (2022): "Heatwaves are increasingly becoming a major public health hazard in India." Analyze the criteria used by the India Meteorological Department (IMD) to declare a heatwave. Evaluate the significance of Heat Action Plans (HAPs) in mitigating heat-related mortalities in urban areas. (15 Marks, 250 Words)

📊 High-Yield Data & Statistical Fact Sheet

Meteorological Risk Profile:
- Cyclone Shift: Arabian Sea has experienced a 52% increase in the frequency of severe cyclonic storms due to rising sea surface temperatures.
- Lightning Mortality: Lightning is the single largest weather killer, causing 2,000–2,500 deaths annually, mainly among rural farmers.
- Early Warning Expansion: IMD is expanding the Doppler Weather Radar (DWR) network to a target of 126 radars for real-time storm track tracking.
- Notified Disaster Gaps: Heatwaves and lightning are not recognized as notified natural disasters under NDRF guidelines, preventing structured federal compensation.

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1. CYCLONES: BAY OF BENGAL VS. ARABIAN SEA

Bay of Bengal (Historically High Vulnerability):
- High Sea Surface Temperature (SST): Consistently warmer basin, fostering cyclonogenesis.
- Freshwater Inflow: Massive discharge from Ganga and Brahmaputra river systems creates a warm, low-salinity surface layer that prevents vertical mixing.
- Low Wind Shear: Promotes the vertical growth of cyclonic storm columns.
Arabian Sea (Emerging Intensification):
- Historically cooler with high wind shear. However, climate change is driving rapid SST warming, causing severe, long-lasting cyclonic storms (e.g., Cyclone Biparjoy).
National Cyclone Risk Mitigation Project (NCRMP): NDMA-led initiative focusing on building early warning dissemination systems, storm-surge shelters, and coastal saline embankments.

The India Meteorological Department (IMD) declares heatwaves based on temperature thresholds:

Declaration Criteria:
- Plains: Maximum temperature reaches $\ge 40^{\circ}\text{C}$.
- Hilly Regions: Maximum temperature reaches $\ge 30^{\circ}\text{C}$.
- Coastal Regions: Maximum temperature reaches $\ge 37^{\circ}\text{C}$.
- Departure from Normal: Declared if max temperature departure is $4.5^{\circ}\text{C}$ to $6.4^{\circ}\text{C}$ above normal. Severe heatwave if departure exceeds $6.4^{\circ}\text{C}$.
- Absolute Max Temp: Declared directly if actual max temperature reaches $\ge 45^{\circ}\text{C}$ (regardless of normal values).
Heat Action Plans (HAPs): Localized municipal action plans implementing early warning temperature alerts, adjusting outdoor labor shift hours to cooler periods, establishing shaded water booths, and deploying reflective cool-roof coatings.

High Rural Mortality: Lightning accounts for more extreme weather deaths than cyclones and heatwaves combined.
Trigger Mechanisms: Triggered during pre-monsoon convective storm clouds when strong updrafts create electrostatic charge separations.
Mitigation Strategies:
- Lightning Mapping Array: Installing electrical ground sensor grids to map lightning discharges.
- CAP-Based SMS Alerts: Sending location-based SMS warning alerts to farmers 30–40 minutes before convective cells discharge.

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Heatwave Threshold (Plains): $\ge 40^{\circ}\text{C}$.
Heatwave Threshold (Hills): $\ge 30^{\circ}\text{C}$.
Severe Heatwave Departure: $>6.4^{\circ}\text{C}$ above normal.
Cyclone Nodal Infrastructure Plan: National Cyclone Risk Mitigation Project (NCRMP).
Storm Tracking Radar: Doppler Weather Radar (DWR) (Target: 126).
Leading Extreme Weather Killer: Lightning (2,500+ deaths/yr).
Critical Physiological Threshold: Wet-bulb temperature (exceeding 35°C human limit).

Notes updated up to March 2026. Sources: IMD Bulletins, NDMA Guidelines.