Cyclone Dana is expected to make landfall as a severe cyclone with wind speeds between 89 to 117 kmph along the Odisha coast, particularly near Bhitarkanika National Park and Dhamra Port. This will be the third cyclone in the North Indian Ocean and the second to make landfall in India in 2024, following Cyclone Remal. Cyclone Dana marks the first cyclone of the post-monsoon cyclone season. The name “Dana” was given by Qatar, and in Arabic, it symbolizes both “generosity” and refers to a valuable, perfectly-sized pearl.
Reasons for Intense Rainfall
The cyclone is generating intense rainfall due to several key atmospheric factors:
- Intense Convection: The cyclone shows strong convection in its western sector, reaching the upper atmospheric layers. Warm, moist air rises, cools, and expands, forming cumulonimbus clouds, which are typical of thunderstorms and promote heavy rainfall.
- Warm Moist Air: There is an influx of warm, moist air into the cyclone’s core, which further enhances the intensity of the rainfall. This process strengthens the cyclone and concentrates rainfall over a small area.
- Madden Julian Oscillation (MJO): The MJO, currently in a favorable phase for enhanced convection, is contributing to increased rainfall. The MJO is a phenomenon where surface winds and rainfall vary between enhanced and suppressed phases. During the enhanced phase, surface winds cause air to rise, leading to increased rainfall.
Naming of Cyclones
The practice of naming cyclones has evolved significantly. Initially, storms were named after saints in the late 1800s in the Caribbean, and during World War II, female names were commonly used. After 1979, the naming convention was updated to include both male and female names, alternating between the two.
- North Indian Ocean Cyclone Naming: In the North Indian Ocean, the World Meteorological Organization (WMO) began naming cyclones in 2000. Thirteen countries including India, Bangladesh, Maldives, Myanmar, Sri Lanka, and Qatar contribute to a collaborative list. Each country suggests 13 names, and the list is periodically rotated to introduce new names while retiring names associated with highly destructive storms.
Key Factors Leading to Cyclone Formation
Several environmental conditions are necessary for cyclone formation:
- Warm Ocean Waters: Sea surface temperatures of at least 27°C are essential, as they provide the heat and moisture needed to fuel rising air and trigger the convection process.
- Coriolis Force: This effect, caused by the Earth’s rotation, is crucial to give the cyclone its spin, with cyclones generally forming at least 5° north or south of the equator.
- Low Wind Shear: Low vertical wind shear ensures the storm’s structure remains intact, enabling it to strengthen.
- Pre-existing Disturbance: A low-pressure system provides the initial organization of air circulation, forming the foundation for cyclone development.
- Convergence of Air: The convergence of warm, moist air at the surface rises and cools, creating clouds and thunderstorms that form the core of the cyclone.
Impacts of Cyclones
Cyclones have wide-ranging impacts on both human life and the environment.
- Human Impact: Strong winds, storm surges, and floods often cause displacement of thousands, sometimes permanently. Homes and livelihoods are destroyed, resulting in long-term social impacts.
- Infrastructure Loss: Power outages, damage to buildings, and disruptions in transportation and communication are common.
- Environmental Damage: Coastal erosion, destruction of forests, wetlands, and marine ecosystems threaten biodiversity. Agricultural productivity declines due to seawater intrusion and waterlogging, leading to extensive crop damage.
- Agricultural Loss: In low-lying areas, heavy rainfall causes waterlogging, which can devastate crops and negatively affect soil health.
The Four-Stage Cyclone Warning System
India has a four-stage cyclone warning system that helps reduce risks:
- Pre-Cyclone Watch (Green): Issued 72 hours before potential cyclonic disturbances.
- Cyclone Alert (Yellow): Issued 48 hours before adverse weather, providing details about the storm’s position and intensity.
- Cyclone Warning (Orange): Issued 24 hours before landfall, offering more detailed updates and advisories.
- Post Landfall Outlook (Red): Issued 12 hours before landfall, predicting inland impacts like flooding and high winds.
Cyclone Preparedness and Mitigation
Effective disaster preparedness includes the following measures:
- Land Use Planning: Strict regulations should govern vulnerable areas to prevent habitation and reserve them for less risky uses like parks.
- Early Warning Systems: The Impact-Based Cyclone Warning System should be used to communicate risks effectively, focusing on local populations.
- Engineered Structures: Buildings should be constructed to withstand cyclone-strength winds, especially vital public infrastructures like hospitals.
- Mangrove Plantations: Coastal areas can be protected through mangrove planting initiatives, which act as natural barriers to storm surges and erosion.
During a cyclone, evacuation shelters should be well-connected to major roads to facilitate evacuation, and sea walls and drainage systems should be implemented to reduce flooding. After a cyclone, hazard mapping should guide rebuilding efforts, and communities should be educated on how to retrofit non-engineered structures to increase resilience against future cyclones.
Classification and Formation of Cyclones
Cyclones can be classified into extra-tropical cyclones, which occur in temperate and high-latitude regions, and tropical cyclones, which form in tropical or subtropical waters. Cyclones are also known by different names worldwide, such as typhoons in the Pacific Ocean, hurricanes in the Caribbean, and tornadoes in West Africa.
In India, the Indian Meteorological Department (IMD) classifies cyclones based on wind speed, storm surges, and rainfall. For example, super cyclones have wind speeds above 221 km/h, while severe cyclonic storms have speeds between 88 to 117 km/h. Cyclones can cause significant damage through storm surges, which are influenced by factors like wind, atmospheric pressure, and coastal geography.
Indian Cyclone Vulnerability
India is particularly vulnerable to cyclones due to its long coastline of 8041 km. The Bay of Bengal is the genesis for the majority of cyclones that strike India’s east coast. On average, 5-6 tropical cyclones form annually in the region, with 2-3 being severe. Cyclones frequently hit both the east and west coasts, with the east experiencing more frequent and severe cyclonic activity.
Cyclones in India are most frequent in the months of May-June and October-November, with the North Indian Ocean region seeing a peak in cyclone activity in November. Storm surges are the most damaging aspect, causing flooding, coastal erosion, and vegetation destruction, severely affecting agricultural lands and coastal communities.
Cyclone Dana serves as a stark reminder of the need for proactive disaster management, improved infrastructure, and community involvement to mitigate the devastating effects of these natural phenomena.