Cyclone Gulab

Context:

A new depression had formed over the east-central Bay of Bengal which intensified into cyclone Gulab which affected the coasts of south Odisha north Andhra Pradesh. It made landfall triggering heavy rains along with strong winds over north coastal Andhra Pradesh and adjoining south coastal Odisha. 

Relevance:

Prelims, GS-I: Geography (Important Geophysical Phenomenon, Climatology), GS-III: Disaster Management

Dimensions of the Article:

1. More about Cyclone Gulab
2. Increasing numbers of cyclones in changing times
3. Cyclones in Bay of Bengal vs Arabian Sea

More about Cyclone Gulab

• Cyclone Gulab comes under the category of the cyclonic storm according to IMD.
• Being a monsoon system, it naturally holds excess moisture compared to storms of pre-monsoon and post-monsoon periods. 
• A couple of unique meteorological factors are also helping the system intensify and retain moisture.
• Because of weak to moderate negative Indian Ocean Dipole (-IOD), the equatorial Rossby waves (natural planetary waves) could have transferred a substantial amount of energy (moisture) to this system.

Increasing numbers of cyclones in changing times

• West Indian Ocean normally sees an extremely small number of cyclones and tropical storms compared to the Eastern side. – Between 1891 and 2000, almost 50 tropical cyclones impacted the west coast, of which more than 20 were severe cyclonic storms. In contrast, about 300 cyclones impacted the east coast of the country from the Bay of Bengal, including more than 100 severe cyclonic storms.
• Cyclones occur in the pre-monsoon months of May-June and the post-monsoon months of October-November.
• However, in the past few decades, the average number of storms to occur over the Arabian Sea and the time of the year when they do have both demonstrated a changing trend.
• In 2018, while the Bay of Bengal maintained its average of 4 cyclones a year, Arabian Sea gave rise to 3 instead of 1. A year later in 2019, the Arabian Sea saw 5 cyclones.
• Overall, there was a 32% rise in the number of cyclones between the years of 2014 and 2019.
• The changing trends are consistent with rising temperatures in the Indian Ocean. A 2014 study found that while the temperature of the Indian Ocean rose overall by 0.7 degrees Celsius, the generally colder western Indian Ocean experienced an unexpected warming of 1.2 degrees Celsius in the summer.
• Additionally, cyclones over the Arabian Sea are also increasing in intensity, driven by rising emissions and temperatures.
• Typically, an extremely severe cyclone occurs once every four to five years in the Arabian Sea, however, extremely severe Cyclone Nilofar in 2014 and Chapal and Megh in 2015, formed over the Arabian sea showing the increasing trend.

Cyclones in Bay of Bengal vs Arabian Sea

Near India, cyclones form on either side of the country, but the ones in the Bay of Bengal are more frequent and more intense than in the Arabian Sea.

Why Bay of Bengal creates significantly more cyclones?

• Apart from being a warm pool region, the Bay of Bengal is slightly more landlocked with South East Asian countries surrounding it, compared to the Arabian Sea, which is more expansive and this also leads to an increase in salinity of the seawater.
• The Bay of Bengal is fed by a constant source of freshwater in the form of giant rivers like the Ganga and the Brahmaputra. The river water that empties into the Bay of Bengal warms up at the surface and rises up as moisture. This makes it difficult for the warm layers of water to mix properly with the cooler layers of water below, keeping the surface always warm and ready to feed any potential cyclone over it.
• Furthermore, because of the shape of the land around the Bay of Bengal, the winds are slower and weaker over the ocean, ready to spin.
• According to experts, the Bay of Bengal also gets many remnants of the typhoons in the Pacific Ocean. They come as a low-pressure area into the Bay of Bengal and grow into cyclones due to ideal conditions.

Why are there lesser cyclones in the Arabian Sea?

• The northern, central and western parts of the Arabian Sea have a much cooler temperature. The mountains in east Africa direct winds towards the Arabian Peninsula, dissipating heat much more efficiently throughout the Arabian Sea.
• As a result, this region is not favourable to feed potential cyclones and about half the cyclones that move into this area typically lose energy and dissipate.

-Source: The Hindu