Two recent cyclones – Amphan (May 20, 2020) and Nisarga (June 3, 2020) – hitting India’s east and west coasts respectively within a fortnight, have energized discussions around environment, disasters, climate change and urbanization affecting the conditions of seas surrounding India. Around the same time last year, in May 2019, pre-monsoon cyclone named Fani hit Odisha in the east coast and caused huge economic damage.
In the northern Indian Ocean that includes the Bay of Bengal and Arabian Sea, there are two peaks of activity with regard to tropical cyclones. Pre-monsoon cyclones occur in May-June and post-monsoon cyclones during October-November, with primary peak in November and secondary peak in May, according to India’s National Cyclone Risk Mitigation Project (NCRMP).
Historically, of the cyclones that develop over the Bay of Bengal, over 58 per cent approach and cross the east coast in October and November. Only 25 per cent of the cyclones that develop over the Arabian Sea approach the west coast. In the pre-monsoon season, corresponding figures are 25 per cent over Arabian Sea and 30 per cent over Bay of Bengal, going by NCRMP data.
Intense summer cyclones
Based upon available data since 1891, Director General of India Meteorological Department (IMD), Dr Mrutyunjay Mohapatra said frequency of cyclones over the Bay of Bengal, which is a cyclone-prone sea, has not increased. “But there is a detectable change over the Arabian Sea in terms of increase in intense and severe cyclones since 1990,” he noted.
Speaking on the frequency of cyclonic systems occurring over the Arabian Sea and flooding events in India’s west coast region, Prof Sridhar Balasubramanian of department of mechanical engineering of Indian Institute of Technology (IIT) Bombay observed, “What used to be once in a century kind of event has now become once in a decade kind of event. Extreme flooding, which was rare in Mumbai, occur once in five years or two-three years now.”
According to Visiting Professor at School of Earth Ocean and Climate Sciences of IIT Bhubaneswar Dr Uma Charan Mohanty, “Pre-monsoon cyclonic systems are more common to the Arabian Sea. We call it monsoon onset vortex, low pressure circulation on the sea surface that mostly becomes a depression, and sometimes a cyclonic storm. Such systems help monsoon reach Mumbai or coastal Maharashtra and Gujarat, earlier than the usual course.”
On the basis of recent events, Prof Mohanty said pre-monsoon cyclones are becoming more intense now and lasting on land areas because land surface is becoming more conducive due to increased temperature.
Warm Ocean brews cyclones
“While increasing temperature due to ocean warming plays a vital role behind genesis of cyclonic storms over the Bay of Bengal and the Arabian Sea, heat transported through ocean current might be energizing the systems,” said former director of IMD, Bhubaneswar, Dr Sarat Chandra Sahu, who is now Director of Centre for Environment and Climate at SOA University.
“We are also seeing frequent occurrences of El Nino and Indian Ocean Dipole events (IOD), which add energy to the seas and the atmosphere to create favourable conditions for cyclone formation,” Balasubramanian said. “Last year’s IOD event was the strongest ever recorded. Over the years, IOD events have risen and become regular and stronger also to influence both Bay of Bengal and Arabian Sea. Such events may be helping intensify the systems adding to cyclone strength.”
Mentioning that post-monsoon cyclones over the Bay of Bengal have greater relationship with IOD, Mohapatra mentioned, “We can expect longer and stronger vertical cyclones here in La Nina conditions.”
As the surface temperature keeps rising in summer, sea surface temperatures (SST) also go up. While 26 degree Celsius of SST is capable of generating cyclonic systems, it goes up to 30-31 degree Celsius over the Bay of Bengal and Arabian Sea in May and June, he added.
Exacerbating sea level rise
Carbon emissions from industries and vehicles, emission of green house gases from various coal factories etc. accelerate the process of temperature rise. Second accelerator is urbanization. “We are concretizing everything. We don’t have enough soil or lot of ground left to absorb the heat from the atmosphere. The heat ultimately goes to sea, making it warmer,” said Balasubramanian.
While temperature rise and ocean warming lead to sea level rise (SLR), its projected consequences are more numbers of extreme sea level events like tropical cyclones with increased intensity and flooding in the coastal regions. The concerns grow immensely as studies project that global sea levels are to rise between 2 and 7 feet, and possibly more, over the course of the 21st century.
According to reports, only 5–10 cm of SLR, expected under most projections to occur between 2030 and 2050, doubles the flooding frequency in many regions, particularly in the tropics including most of coastal India. Increasing annual floods could affect 36 million people living in coastal areas while hitting economy of megacities like Kolkata, Mumbai and Chennai, according to a projection of land area below annual flood level in 2050.
Give space to Nature
Experts attribute coastal ecological and environmental degradation to destructive impact of cyclones and floods. Despite the fact that mangroves are the best protection against storm surges and floods, mangrove cover along the coast is under tremendous threat. Among several other reasons, coastal erosion is one of the major threats to the existing mangrove covers, suggests a study led by Radhika Bhargava of the geography department of National University of Singapore.
Mapping loss in the Sundarbans, Bhargava claimed mangrove erosion between 1984 and 2018 in the region amounted to 136.77 square km accounting for 27.55 per cent of total cover. The area under progradation or accretion during the same time remained 62.17 sq km, 12.52 per cent. “Neither is adequate inland space available for the mangroves to expand nor is the accreted land mass reclaimed.”
Even though the government has programmes for mangrove protection and plantation, community awareness on importance of mangroves is more essential for its conservation, said Dr Amlesh Mishra, a former senior scientist of Zoological Survey of India. Mishra runs Paribesh Unnayan Parishad (PUPA), a non-profit organization that works for development and spreading scientific temper among children and communities of Sagar Island.
“With 30 bio-clubs of school students we create awareness on the necessity and conservation of mangroves. This apart, we also expose these students to resilient agriculture in the wake of climate change,” he said.
While the government of Maharashtra has woken up to the issue of loss of mangroves and formed a separate cell for its protection, NGOs like iNaturewatch are engaged in creating awareness among communities and engage them in conservation activities.
“We also conduct free awareness programmes in schools for environmental awareness and inculcating environmentalism in the coming generation,” said Isaac Kehimkar, former deputy director of Bombay Natural History Society and currently director of iNaturewatch. Such activities need to be expanded to all coastal communities, he urged.
While embankments are necessary in high erosion areas to protect the cities, coastal cities like Mumbai need to conserve the natural habitats available to enhance preparedness to face future storm surges. Insisting on strict regulations for urban development, Balasubramanian highlighted, “We are concretizing everything. This makes the city vulnerable to extreme weather events because we don’t have enough soil area or ground left to absorb the heat from the atmosphere and the water during heavy rain and floods.”
