Context:
Science Minister said that the frequency of “very severe cyclonic storms” has increased in recent years over the Arabian Sea.
Relevance:
GS-I: Geography (Physical geography – Climatology, Important Geophysical phenomena), GS-III: Environment and Ecology (Impact of Climate Change), GS-III: Disaster Management
Dimensions of the Article:
- Highlights of the Science Minister’s response on Cyclones
- Increasing numbers of cyclones in changing times
- Bay of Bengal vs Arabian Sea
- Increasing Cyclones in Arabian Sea
Highlights of the Science Minister’s response on Cyclones
- Although the frequency of “very severe cyclonic storms” (A very severe cyclone is defined as one with windspeeds touching 220 kmph) has increased in recent years over the Arabian Sea, has not measurably increased the threat to India’s western coast, as most of these cyclones were making landfall in Oman and Yemen.
- The number of cyclones and stations reporting very heavy and extremely heavy rainfall events have increased in recent years.
- An analysis of past data of cyclones over North Indian Ocean (Bay of Bengal and Arabian Sea) during the period from 1891 to 2020 indicates that the frequency of “very severe cyclonic storms” has increased in the last few years over the Arabian Sea.
- However, the Eastern Coast of India remained far more vulnerable to “Extremely Severe Cyclones” than the Western coast, but there was nevertheless “no significant trend” in the frequency of Extremely Severe Cyclonic Storms (ESCS).
- On an average, 60%-80% of the cyclones developing over the North Indian Ocean (NIO), comprising Bay of Bengal and Arabian Sea, made landfall causing loss of life and property.
- Low lying coastal belts of West Bengal, Odisha, Andhra Pradesh and Tamil Nadu and Puducherry were more prone to the impact of these systems.
- The number of deaths due to cyclones has decreased significantly, as a result of the improvement in the early warning skill of the India Meteorological Department (IMD) under the Ministry of Earth Sciences (MoES), and effective mitigation measures and response actions by the National Disaster Management Authority (NDMA) and Ministry of Home Affairs (MHA).
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.
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.
Increasing Cyclones in Arabian Sea
- For the past 150-200 years, the Bay of Bengal has given birth to four times more cyclones than the Arabian Sea. But this may soon change, thanks to global warming.
- A study by The Indian Institute of Tropical Meteorology has shown that both the frequency and intensity of cyclones in the Arabian Sea are on the rise. The experts believe the key reason is a rise in the ocean temperature.
- Traditionally, the Arabian Sea is a lot cooler than the Bay of Bengal. But now the Arabian Sea is also becoming a warm pool region because of the additional heat supplied by global warming.
-Source: The Hindu
