In Sagar Island, on the Indian side of Bengal, environmental activist Pranabesh Maiti thought he was prepared to brave cyclone Amphan, which hit the Bay of Bengal on May 20, 2020.
Maiti and other islanders of the flood prone region were taken aback by the intensity of the cyclone due to the accuracy of past weather forecasts. Comparatively, cyclone Bulbul in November 2019 was easier to get through.
The government had warned the 200,000 inhabitants of Sagar CD Block in advance, part of the Indian Sundarbans islands, about 100 km from the east coast Indian city of Kolkata, who moved their livestock to safe hideouts and covered all their grain stock.
Residents took shelter wherever possible as, they say, the government has not built enough cyclone shelters to date. Despite these preventive measures, things didn’t go as planned.
Recollecting the events of that fateful day, Maiti, who works for the Sundarbans Green Environment Association, says that between noon and 3 pm, a dust storm filled with saline particles blew away 70% of the homes. Residences were made from asbestos, leaves and straw.
Flooring tiles flew rapidly in the air like a pack of cards. Telephones went offline, so residents could not call for help. “The strong gushes of wind were choking me. It was so bad I thought the island may submerge,“ Maiti remembers.
What caused the rapid intensification of Cyclone Amphan? Within 18 hours, the storm went from a relatively weak cyclone at 100-150 km/h to a Super Cyclonic Storm at 200-250 km/h.
During the two intense cyclones of 2020, including cyclone Nisarga, the sea surface temperature (SST) reached 32-33 degrees Celsius, hitting a new record. Usually, this figure doesn’t surpass 31 degrees. In the Indian Ocean, extreme events with such high temperatures are referred to as marine heatwaves.
“Cyclones generally draw their convective energy from warm waters, riding on a global warming background that ends up supercharging cyclones,” said leading climate scientist Dr. Roxy Mathew Koll. He works with 35 other scientists at the Centre for Climate Change Research, Indian Institute of Tropical Meteorology.
Updating the Indian Ocean Observing System (IndOOS)
Koll is the co-author of a recent review that evaluated the accuracy and effectiveness of the Indian Ocean Observing System (IndOOS), an international network of oceanic instruments, that collect data and feed them to climate models used by countries close to the Indian ocean.
Weather and climate models used by the Indian Meteorology Department (IMD) were developed by his colleagues at IITM and IMD. The problem? In the case of cyclones, the forecasts don’t give advanced warning, especially on rapid intensification. In such cases, IndOOS-2, an upgraded version of the observing system, can help by studying more oceanic parameters with high resolution data.
“Weather forecasts don’t incorporate ocean measurements. Cyclone forecasting must take this into account. With IndOOS-2, for example, studying the ocean’s subsurface layer’s characteristics is recommended. This data would help forecast the intensity of the incoming cyclones, which current models are unable to predict,” Koll explains.
Weather models provide data for weather forecasts with 90% accuracy, albeit they still have many gaps to fill that would help governments be better prepared.
According to a study, in contrast to global rises in SST between 1951-2015 at 0.7 degrees Celsius, the Indian Ocean’s SST rose by one degree Celsius over the same period.
This is a matter of concern because this ocean basin has one of the largest concentrations of marine phytoplankton. “In recent times, ocean surface warming has decreased the density of surface waters, preventing the mixing between the subsurface and surface. As the two layers mix less, available nutrients in the subsurface, such as nitrogen, phosphate and iron become less available to phytoplankton,” Koll said.
Consequently, the fish population declined, as phytoplankton is what they feed on. In 2019, Sardine catch in Kerala reached its lowest point in 20 years.
This compound effect on temperature and fish population is not taken into account by current climate models, for example, the 26 CMIP5 suites. Right now, only physical parameters such as salinity, temperature and ocean pressure are studied.
Floats, drones and gliders
The review suggests adding more Argo floats, a steel cylinder about 1 to 1.5 m in height that records data, eventually sent via a satellite to climate models.
Koll explains that Argo floats used by the IndOOS network generally go until 1000 m deep, and come back up after a ten-day interval. Instead, the review recommends Argo floats that can go beyond 2000 m deep. “This is important if we want to know how much heat is stored in the Indian Ocean due to climate change”
Also, the heat budget, a calculation of how much heat is coming and escaping the Western Indian Ocean, through the Indonesian Throughflow and Agulhas current, has been only sporadically studied, through a few university-funded projects. A large portion of this area falls on the Somalian coast, where pirates are known to hijack commercial ships, which made monitoring of this region difficult, along with the strong ocean currents that dismantle moorings and buoy chains.
Due to unforeseen challenges in this region, “we need measurements at varied depths of ocean water at different locations. We have suggested the usage of gliders and sail drones, in some of those regions such as small straits, that could better accomplish this job,” Koll explains.