Climate Change

Ocean surface waves — and their hazards — due to tropical cyclones are growing bigger, warns study

Maximum height of tropical cyclone waves, area of its footprint has increased significantly over 40 years

By Susan Chacko
Published: Monday 08 January 2024
Photo: iStock

Ocean surface waves brought on by tropical cyclones (TC) have increased over time, according to a new study, which has cautioned that these could be a concern in the future. Both the maximum height of these waves and area of the wave footprint have increased significantly and these changes are larger than those of the TC maximum wind speed, the paper found. 

The researchers analysed 43 years’ of data on global trends in the ocean surface waves induced by tropical cyclones (TC) waves. The study was published in journal Nature Communications on January 3, 2024. 

A TC is a warm-core low pressure system that develops over tropical or subtropical waters and has an organised circulation. These include hurricanes and typhoons. TCs produce high winds, large waves, extreme water levels and heavy rainfall. 

The maximum height and the area of these wave footprints have increased globally by about 3 per cent per decade and 6 per cent per decade, respectively, the paper stated. The energy of these waves, transferred at the interface from the atmosphere to the ocean, has increased globally by about 9 per cent per decade, which is three times larger than that reported for all waves, the study said.

The fastest-increasing rates of TC wave footprint (17-32 per cent per decade) were in the North Atlantic, eastern Pacific and North Indian Ocean. According to the researchers, the rise in wave area is the primary cause of the trend of rising global wave energy.

All ocean basins show a significant long-term increase in the maximum wave height, with the largest increase of 5 per cent per decade in the North Atlantic. 

Tropical cyclones play an important role in maintaining the energy balance at the air-sea interface. TCs take heat energy from the ocean surface to fuel their development. On the other hand, they also dissipate kinetic energy into the ocean through waves.

The study, led by Jian Shi, Hohai University, China, looked at the global trend analysis of tropical cyclone waves for 1979-2022 based on the ERA5 wave reanalysis.

ERA5 is the fifth generation European Centre for Medium-Range Weather Forecasts’ atmospheric reanalysis of the global climate, covering the period from January 1940 to present. It provides hourly estimates of a large number of atmospheric, land and oceanic climate variables. 

Tropical Cyclone Freddy was a long-lived tropical system that traversed the Indian Ocean and seriously impacted Madagascar, Mozambique and parts of southeast Africa with intense rain and flooding. Freddy dissipated over Malawi March 15, 2023 after a record-breaking 37-day stint over the southern Indian Ocean and Africa.

Research published June 20, 2023 in the journal Proceedings of the National Academy of Sciences found tropical cyclones cause ocean turbulence that extends deeper than previously thought, causing mixing that transfers heat from the surface to waters nearly 300 metres down.

The researchers suggested that the ocean warming caused by tropical cyclones goes deep enough to persist for months or years and travel far from its point of origin, potentially altering the broader patterns of ocean circulation that partly regulate Earth’s climate.

TCs cause extensive damage through strong winds and heavy rainfall causing destructive oceanic extremes such as storm surges and surface waves, posing substantial threat to infrastructure, navigation and communities. 

Intense tropical cyclones can slow down the economic development of a country and India’s long-term economic damages from tropical cyclones are expected to range from $43-47 per tonne of carbon dioxide, according to a study published in journal Nature Communications.

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