Climate Change

Spike in sea temperatures, cyclones increase in Indian Ocean region: Report

Temperature rise 0.3°C higher than the global average of 0.7°C; last two years see significant rise in number, intensity and unpredictability of cyclones

By Akshit Sangomla
Published: Friday 19 June 2020

Increasing sea surface temperatures in the tropical Indian Ocean and an increase in frequency of very severe cyclones in the region were pointed out by the first climate change assessment report published by the Union Ministry of Earth Sciences on June 17, 2020.

Sea surface temperatures in the tropical Indian Ocean rose by one degree Celsius on average between 1951-2015, said the report, titled Assessment of Climate Change over the Indian Region.

This temperature rise was 0.3°C higher than the global average of 0.7°C, according to the report. Ocean heat content in the top 700 metres of the tropical Indian Ocean also rose in the same period, with the past two decades displaying an abrupt rise.

Oceans absorb around 90 per cent of the warming caused by greenhouse gas (GHG) emissions that can, in turn, lead to more intense cyclones, sea level rise and faster melting of polar ice shelves.

Sea levels in the North Indian Ocean (NIO) region rose by 3.3 millimetres every year between 1993 and 2017, almost double the maximum rate of 1.75 mm per year measured between 1874 and 2004, the report said.

The frequency of very severe cyclones also increased in the region by one per decade in the last two decades even though overall frequency of cyclones decreased in the latter half of the last century and the first two decades of the 21st century, said the report.

The last two years saw a significant rise in number, intensity and unpredictability of cyclones in the NIO region, the latest being super cyclone Amphan in the Bay of Bengal and very severe cyclone Nisarga in the Arabian Sea.

All these trends will continue to rise if GHG emissions are not curbed. Global warming from GHG emissions presents unique challenges for India.

“Monsoon extremes are unique to India: More intense wet periods and more frequent and longer dry periods with widespread floods and droughts,” said Raghu Murtugudde, a climate scientist at the University of Maryland, US.

“This is combined with more intense cyclones and sea level rise, making India one of the most vulnerable countries,” he added.

This also held significance for regional geopolitical stability, as vulnerabilities of the country’s neighbours end up becoming national security and humanitarian crises, something already obvious in the Rohingya issue, according to Murtugudde.

There was already a spike in extreme weather events over the region because of the observed change of 0.7°C in average temperatures over India, said Roxy Mathew Koll, a climate scientist at the Indian Institute of Tropical Meteorology, Pune.

“Rainfall patterns have changed. There are longer dry spells intermittent with heavy rainfall events. The frequency of very severe cyclones has increased over the Arabian Sea,” he said. “Over the Himalayas, the glacier retreat is going at a fast pace. Glacier melt and ocean warming raised sea level across the Indian Ocean,” he added.

Recent records showed a sea level change of three centimetres per decade along the Mumbai coast, with a change of five centimetres per decade along the Kolkata coast, according to Koll.

Temperatures are projected to rise by 2.7°C by 2040 and 4.4°C by the end of the century, according to the report.

The region should be ready to face a further increase in intensity, frequency and extent of extreme weather events, according to Koll.

The chances of such events overlapping were also large, multiplying the threat.

“We call them compound events. For example, an intense cyclone may be accompanied by heavy rain and storm surges as in the case of the recent cyclones. Droughts may occur along with heatwaves,” said Koll.

Local environments, with high population densities and land use conditions can increase risk and vulnerability to such events as well.

This is where installing early warning systems that integrate multiple threats can help, Koll pointed out.

“Recently a flood warning system was installed in Mumbai on an experimental basis. Such a flood warning system takes topography, city’s drainage and water bodies, tidal levels and rainfall data into consideration and tells us the extent of flood that can happen at different pockets of the city,” he said.

The first step towards climate resilience was to replicate such efforts, Koll added.

India also needs to take up more attribution and modelling studies to understand climate change impacts in a clearer way.

There have not been many attribution studies on monsoon trends. It may be better, however, to focus modelling efforts on improving weather and climate predictions and regional projections for the short-term, according to Murtugudde.

“Adaptation to expected impacts will be the most critical with efforts to mitigate the impacts,” said Murtugudde, citing the example of afforestation and mangrove forest recovery.

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