askST: Why does lightning strike without rain and what is a ‘bolt from the blue’?

SINGAPORE – Singapore logs one of the highest lightning strike rates in the world.

On July 5, a man died after he was struck by lightning while paddleboarding in the waters off Pasir Ris Beach. An eyewitness said that the skies appeared clear when lightning struck the sea.

The Straits Times asked weather scientists about lightning strikes and how people can stay safe.

Q: Can lightning strike even when there is no rain?

A: Once a storm begins to form, there is always a risk of lightning even though there is no rainfall yet, said National University of Singapore adjunct associate professor Koh Tieh Yong, who researches the weather and climate of South-east Asia.

Lightning is a large electrical spark caused by the difference in charges between storm clouds and the ground, or within the clouds. It discharges in a blinding flash.

“Lightning forms when air is moving vigorously, causing cloud droplets to bump into one another and acquire electric charge,” Koh said. “But rainfall is observed at Earth’s surface only when the water droplets grow big enough to fall all the way down.”

While the two processes are related, neither needs the other to occur, he added.

Q: How can a bolt from the blue strike faraway locations?

A: Lightning has been known to strike more than 10km away from a parent thunderstorm cloud, although the frequency of these occurrences is very low, according to the Meteorological Service Singapore’s book, Weather And Climate Of Singapore.

Such strikes are known as a “bolt from the blue”.

In Singapore, only cumulonimbus clouds can form lightning. They are extremely tall clouds distinguished by their puffy grey appearance and flat anvil-shaped top.

While much rarer, strikes originating from the anvil-shaped top of cumulonimbus clouds can hit faraway areas, including places with blue skies and no rain.

These powerful electrical discharges, known as “positive lightning”, make up about 10 per cent of strikes from a thundercloud to the ground.

Q: Why does Singapore get so much lightning?

A: As Singapore sits in the equatorial belt, where the Earth’s surface is always hot and the air is always humid, the atmosphere is in an unstable state most of the time and thus ready to spawn thunderstorms, said Koh.

Annually, on average, there are about 176 days when lightning is detected at Singapore’s Changi climate station. This amounts to nearly one in every two days each year.

Q: What happens when someone is struck by lightning, and can I help?

A: Those struck by lightning can suffer a range of injuries, including burns, cataracts and fractured skulls. They can also get psychological injuries such as post-traumatic stress disorder or depression.

Victims of lightning strikes are safe to touch as the human body does not store electricity, according to the US National Weather Service.

Nanyang Technological University climate researcher Wang Jingyu said bystanders should check the breathing and pulse of the victims. If these signs are absent, they can start cardiopulmonary resuscitation and use an automated external defibrillator.

Prompt action can help save a victim’s life, he said, adding that the person should be moved only if the area remains at risk.

Q: Will El Nino and climate change increase lightning activity?

A: Warmer and drier than normal conditions are expected in the coming months in Singapore as a result of the El Nino weather phenomenon.

El Nino is a climate phenomenon that results in less rain, longer dry spells and higher temperatures for the region.

It is caused by a natural cycle called the El Nino-Southern Oscillation, when changes in winds and sea surface temperatures shape weather patterns over the Pacific Ocean, which covers about one-third of the planet.

It also influences the distribution of thunderstorms, with less frequent storms expected in the Malay Archipelago where Singapore is located, according to Koh.

“But the specific impact on lightning discharges in individual storms is hard to establish as many other non-systematic small-scale factors are at play,” he added.

Koh said more research is needed to understand how climate change impacts thunderstorms.

Q: What precautions can I take to avoid being struck by lightning?

A: People should take heed of weather forecasts when planning outdoor activities and take note of where the nearest permanent shelters are.

They can also subscribe to real-time lightning alerts on the Government’s myENV app.

Wang said lightning forecasting is extremely difficult and even when forecasts are available, they are based on probability.

He added: “Even for Singapore, a forecast cannot pinpoint exactly where a strike will occur. Therefore, we should not rely solely on government warnings or ignore the risks. Ultimately, we are the first and primary responsible party for our own safety.”

He advised people to seek shelter immediately when thunder is heard more frequently.

Those participating in water sports like sailing, canoeing, swimming or diving should immediately return to shore once they sense that a storm is threatening to form.

Said Wang: “If lightning is spotted, get out of the water immediately. Water is an excellent conductor of electricity and a strike can travel long distances through it.”

If it is too late to escape, swimmers or divers should stay low in the water and keep their head and arms down, he added.

Those on small boats and canoes can lie flat on the bottom of their craft and avoid touching metal parts.

“While these measures won’t guarantee safety, they may reduce the severity of injury if a strike occurs,” said Wang.

These are some other precautions: