Cyclones & Heatwaves: Atmospheric Storms

1. CYCLONES: BAY OF BENGAL VS. ARABIAN SEA

Cue Words	Notes
Bay of Bengal: Historically High Vulnerability	**High Sea Surface Temperature (SST)**: Consistently warmer basin, fostering cyclonogenesis. **Freshwater Inflow**: Massive discharge from the Ganga-Brahmaputra system creates a warm, low-salinity surface layer that prevents vertical mixing. **Low Wind Shear**: Promotes vertical growth of cyclonic storm columns.
Arabian Sea: Emerging Intensification	Historically cooler with high wind shear, but climate change is driving rapid SST warming, causing severe, long-lasting storms (e.g., Cyclone Biparjoy). Arabian Sea severe cyclonic storm frequency has risen roughly 52% in recent decades due to warming SSTs.
2025 Season: A Record-Costly Year	The 2025 North Indian Ocean cyclone season was the **costliest on record** and deadliest since 2008, with over 3,100 fatalities and ~$22.3 Billion in damage; Cyclone Montha alone struck Andhra Pradesh, Odisha and Tamil Nadu with ~$760 Million in losses. **NCRMP**: NDMA-led National Cyclone Risk Mitigation Project continues to build early-warning dissemination systems, storm-surge shelters, and coastal saline embankments — credited with cutting cyclone mortality to under 2% over the past decade despite rising storm intensity/cost.
Structural & Nature-Based Mitigation	**Coastal Exposure**: India's **7,516 km coastline** leaves nearly 8% of its landmass vulnerable to tropical cyclones; the historical Bay of Bengal-to-Arabian Sea cyclone ratio of roughly **4:1** is narrowing as Arabian Sea SSTs warm. **Storm Surge, Not Wind**: The principal killer in a cyclone landfall is the storm surge — a wall of seawater pushed ashore causing sudden inundation and soil salinisation — rather than wind speed itself. **Mangrove Bio-Shields**: Dense mangrove belts reduce incoming wave energy by up to **66% over 100 metres of forest thickness**, trapping sediment and protecting embankments from erosion; Casuarina shelterbelts serve a similar wind-breaking role. **Underground Cabling**: Converting overhead power/telecom lines to underground systems in high-vulnerability coastal towns to restore electricity and communications within hours of landfall, supporting a "zero-casualty" evacuation doctrine built on precise IMD landfall forecasting (e.g., Cyclones Biparjoy, Amphan).

> **Summary**: Bay of Bengal remains structurally more cyclone-prone (SST, freshwater layering, low shear), but the Arabian Sea's rapid post-2015 intensification — culminating in the record-costly 2025 season — shows India's west coast now needs NCRMP-grade protection too; storm surge (not wind) drives most fatalities, which is why mangrove bio-shields and underground cabling matter as much as shelters.

2. HEATWAVES: IMD CRITERIA & HEAT ACTION PLANS (HAPs)

Cue Words	Notes
IMD Declaration Thresholds	**Plains**: Max temperature ≥40°C. **Hilly Regions**: ≥30°C. **Coastal Regions**: ≥37°C. **Departure from Normal**: Heatwave if departure is 4.5°C–6.4°C above normal; severe heatwave if departure exceeds 6.4°C. **Absolute Threshold**: Declared directly if actual max temperature reaches ≥45°C, regardless of normal values.
Heat Action Plans & the Notification Gap	**HAPs**: Localised municipal plans with early-warning alerts, adjusted outdoor labour hours, shaded water booths, and reflective cool-roof coatings; the **Ahmedabad HAP (2013)**, India's first city-level plan, cut heat-related mortality by **30-40%** through colour-coded alerts and cool-roof retrofits and became the template for over 100 city/state HAPs since. **Wet-Bulb Threshold**: Beyond a **35°C wet-bulb temperature**, the human body loses its ability to cool itself via perspiration, making this the physiological ceiling for fatal heat stroke risk — distinct from and often reached well before IMD's dry-bulb heatwave thresholds. **Urban Heat Island (UHI)**: Dark tar/concrete surfaces absorb daytime thermal energy and radiate it at night, keeping cities up to **5°C warmer** than surrounding rural areas; passive cooling fixes include high-albedo cool-roof paint (lowering indoor temperature by 2-5°C) and expanding urban green cover/water bodies. **Labour Productivity Loss**: ILO estimates India could lose **5.8% of working hours** to heat stress, equivalent to over **34 million full-time jobs**, concentrated among outdoor agriculture, construction, and gig workers. **India Cooling Action Plan (ICAP)**: Targets a 20-25% reduction in cooling demand and 25-30% reduction in refrigerant demand via energy-efficient green building codes. **2025 Heat Toll**: The April–July 2025 India-Pakistan heatwave saw peak temperatures of 48°C at Sri Ganganagar, Rajasthan, and caused 455+ recorded deaths in India — reinforcing that heatwaves remain India's most underreported mass-casualty hazard. **Notification Gap**: Heatwaves and lightning are still *not* notified disasters under the DM Act, denying structured NDRF compensation; the **16th Finance Commission (Nov 2025)** has recommended formally adding both to the notified list given their toll routinely exceeds local coping capacity. Tamil Nadu has separately become the first state to recognise heat stress as a *state* disaster under its own SDRF flexibility, enabling relief funding ahead of any central notification.

> **Summary**: IMD's threshold-based heatwave criteria feed into localised HAPs, but the 2025 heat season's high death toll has renewed pressure — now backed by the 16th Finance Commission — to close the long-standing gap of heatwaves not being a notified disaster.

3. LIGHTNING DISASTER DYNAMICS

Cue Words	Notes
Rural Mortality & Trigger Mechanism	Lightning is India's single largest weather killer, causing 2,000-2,500 deaths annually, mainly among rural farmers — more than cyclones and heatwaves combined. Triggered during pre-monsoon convective storm clouds when strong updrafts create electrostatic charge separations.
Mitigation Strategies	**Lightning Mapping Array**: Ground sensor grids mapping lightning discharges. **CAP-Based SMS Alerts**: Location-based warnings sent to farmers 30-40 minutes before convective cells discharge. IMD continues expanding the **Doppler Weather Radar (DWR)** network toward a target of **126 radars**, improving both cyclone tracking and short-range convective/lightning forecasting.

> **Summary**: Lightning's outsized rural death toll stems from a forecasting-to-last-mile-alert gap that Lightning Mapping Arrays and CAP-based SMS warnings are only partially closing, even as the underlying DWR network expands.

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)
• Lightning as an Underrated Hazard: Discuss why lightning causes more annual deaths in India than any other meteorological hazard, and evaluate the case for notifying it as a disaster under the DM Act. (10 Marks, 150 Words)