Torrential rain and severe flooding has been seen across East Asia as three typhoons have hit in just a number of weeks. 

We asked researchers at the National Centre for Atmospheric Science to explain what typhoons are, and what effect climate change is having on them.

Hurricanes, typhoons, and tropical cyclones are all different names for the same type of tropical storm, also known as a tropical cyclone.

“Tropical cyclones are characterised by strong winds, heavy rains, and an ‘eye’ in the centre of a warm-core, low pressure rotating weather system,” explains Xiangbo Feng, climate researcher at the National Centre for Atmospheric Science and the University of Reading.

Whether a tropical cyclone is called a hurricane, typhoon or cyclone, depends on where in the world it develops. When a tropical cyclone develops over the Northwest Pacific Ocean and its winds reach speeds of 74 miles per hour, it is called a typhoon. 

When a tropical cyclone at the same intensity scale forms in the eastern North Pacific and North Atlantic, it is called a hurricane. While in the South Pacific and Indian Ocean, the general term tropical cyclone is used regardless of the storm intensity.

Typhoons typically affect the Philippines, Vietnam, China, South Korea and Japan, and can rarely affect Indonesia and North Korea. Typhoons Talim, Doksuri and Khanun have significantly affected the Philippines, China, South Korea and Japan within the last three weeks.

Dr Feng explains how typhoons form:

“Typhoons develop out at sea. Most of them form east of the Philippines and originate from synoptic-scale atmospheric disturbances. When propagating westward into the warm pool region due to the easterly steering flow, some systems grow into typhoons because of the warm ocean, air moisture, and low vertical wind shear.”

Some typhoons keep moving westward, e.g. typhoon Talim, putting the Philippines and Vietnam at risk. Some recurve north, e.g. typhoons Doksuri and Khanun, often striking the coastal regions of China, South Korea, and Japan.

“Typhoons usually become weaker when approaching coastal regions and migrating north, with some further transformed to extra-tropical cyclones in the process known as extratropical transition. After making landfall, typhoons normally lose the cyclone feature, and are referred to as remnants. The remnant, an inland system, can still lead to heavy rain and flooding, which was partially the case in last week’s flooding in Beijing,” adds Dr Feng.

Human-induced climate change is driving an increase in global temperatures. 

Warmer temperatures provide favourable conditions for typhoons to become more hazardous, as the higher humidity in warmer air and the warmer sea surface temperatures could lead to stronger tropical storms.

Prior to the typhoons, East Asia experienced record breaking temperatures during the heatwaves in June 2023. Beijing recorded its hottest June day since record keeping began in 1961, with temperatures reaching 41.1°C.

South Korea has also experienced a heatwave in recent weeks, with some parts of the country recording temperatures exceeding 38°C. Typhoon Khanun has since struck South Korea, bringing heavy rain and winds.

“These typhoons were accompanied by severe heatwaves. Typhoon-heatwave events could be much more dangerous than the individual extreme events,” warns Dr Feng.  

The last report from the International Panel on Climate Change (IPCC) looked at tropical cyclones region by region. For East Asia the report concluded that the rate of intensification and number of strong tropical cyclones has increased, and tropical cyclone tracks have likely migrated poleward.

A recent study, led by research scientists at The National Centre for Atmospheric Science, showed that over the last four decades, the average position of typhoons has shifted northward by 300 km (78 km/decade). The northward migration occurs throughout the whole life cycle of a typhoon, from where the storm forms through to where the storm disappears.

“Climate change is anticipated to play a major role in this systematic change in typhoons. These new findings suggest that the risk of typhoon-related hazard exposure in China, South Korea, and Japan is likely to be higher in the future,” explains Dr Feng.

Accurate forecasts of typhoons are crucial for protecting lives, livelihoods and infrastructure. Researchers at the National Centre for Atmospheric Science and the University of Reading are currently working closely with national meteorological agencies in countries in Southeast Asia and China to develop new forecasting methods for typhoons. 

Typhoon Khanun is the third typhoon to hit East Asia in recent weeks, closely following typhoons Talim and Doksuri.

The typhoons have caused torrential rains and severe flooding across East Asia, prompting mass evacuations, destroying infrastructure, and affecting the lives and livelihoods of thousands of people. 

Between 29 July – 2 August 2023, Beijing experienced an extreme rainfall event, with nearly the average rainfall for the entire month of July falling on Beijing in just 40 hours.

“Beijing experienced an accumulated rainfall of 744.8 mm, making this rain event the heaviest one during the last 140 years. This extreme rainfall event was caused by the remnants of Typhoon Doksuri, one of the worst storms to hit northern China in years, and also possibly caused by the remote effect of Typhoon Khanun which transports moisture from the tropics,” explains Buwen Dong, climate researcher at the National Centre for Atmospheric Science and the University of Reading. 

Due to the level of flooding in Beijing, flood waters were diverted into the neighbouring Hebei Province in order to limit the damage done to the capital. This has sparked controversy and discussions about how extreme weather events often have a greater impact on disadvantaged populations.

As global temperatures continue to rise, the destruction caused by typhoons will be exacerbated and there will be an increased need for risk adaptation and resilience to these types of extreme weather events – especially in regions that are disproportionately affected by these events. 

Understanding the effect of climate change on typhoons – including the frequency, size, intensity, and the natural and societal impacts – remains a priority in the climate research community.