arts of the Punjab and Khyber Pakhtunkhwa, as well as the federal capital, were hit recently by extreme weather events that left a trail of shattered roofs, wrecked cars and stunned citizens. This wasn’t just a case of extreme weather. Some scientists are saying that these are signs of a changing climate. They say the warmer weather is making hailstorms more frequent and more destructive.

As temperatures climb, the air can carry more moisture making for larger hailstones to form miles above the ground before crashing down on towns and fields.

The most recent storm followed several dry and hot days in the northern part of the country. The region then witnessed ‘vertical instability’—when hot air rising from the plains of the Punjab came in contact with cold winds from northern Iran.

Explaining how hailstorms develop, Dr Sardar Sarfraz, a former chief meteorologist, said: “As the countryside warms with higher temperatures, more moisture-laden air rises via stronger thunderstorm updrafts.” These carry the moisture to the colder parts of the atmosphere, where the temperature can be as low as -40°C.

Hailstones form in high, vertical cumulo-nimbus clouds that produce severe thunderstorms. Within these clouds, the ice particles develop from super-cooled water. Iterations of the process causes “the small ice particles to grow large.”

Changes in speed and direction allow the winds to go farther and rotate. The mid-level updraft rotation appears to be extremely important in suspending hailstones at a near-constant altitude.

Hailstorms strike almost every year. The damage they cause depends on both the amount of hail and the size of the stones. Large volumes of small hail can defoliate trees and crops. In urban areas, hail generally needs to exceed 30 mm (1.2 inches) in diameter to damage roofs, vehicles and windows.

Accurately measuring and describing hail is difficult. Stone size and quantity can change dramatically over just a few hundred metres. The fact that they melt quickly only makes reliable observation harder. Hail size is often estimated by comparing it to a known object. They are typically described in ascending size: pea-size (¼”), mothball-size (½”), penny-size (¾”), nickel ( ”), quarter (1”—hail this size or larger is considered severe), ping-pong ball (1½”), golf ball (1¾”), tennis ball (2½”), baseball (2¾”), teacup (3”), softball (4”), and grapefruit (4½”).

Dr Sarfraz noted that while “the timing of a hailstorm can be predicted, it is still difficult to estimate the size.” The direction and distance of falling hailstones are determined by the wind’s speed and direction and the size of the hailstones. “Smaller hailstones can be blown away by winds but bigger ones fall closer to the storm’s centre. The hailstorms that inflict damage to solar panels, wind turbines, cars, windows and injure people and animals are caused when strong winds near the ground make hail fall at an angle or sideways,” he said.

Hailstorms can be deadly. One of the most tragic incidents of the kind occurred in Bangladesh in 1986, when the heaviest hailstone ever recorded fell in the Gopal-Ganj district. It weighed 1.02 kilograms (2.25 lbs). That storm claimed 93 lives and left more than 300 people injured.

Beyond their human toll, hailstorms frequently bring chaos to roads and urban infrastructure. When layers of hailstones accumulate rapidly, roads can turn dangerous as they prevent tyres from making proper contact with the surface.

Across the globe, hail has caused staggering economic damage. In Leicestershire, England, a storm on July 21, 2021, unleashed golf ball-sized hailstones that shattered windows and battered vehicles. Just a year earlier, in June 2020, Calgary, Canada, was hit by a storm that produced tennis ball-sized hail, damaging 70,000 homes and vehicles and racking up a repair bill of C$1.2 billion.

Changes in speed and direction allow winds to live longer and form spirals. This mid-level updraft rotation appears to be extremely important in suspending hailstones at a near-constant altitude. 

In the United States, a devastating hailstorm near Phoenix, Arizona, in October 2010 dropped hailstones as large as 7.6 centimetres (three inches), causing $2.8 billion in damages. That same year, the largest hailstone ever recovered in the US fell in South Dakota. It measured 20 centimetres (eight inches) in diameter and weighed nearly 0.9 kilograms (two pounds).

While hailstorms wreak havoc on the ground, the danger extends high into the skies as well—posing a serious risk to aviation. Between 2017 and 2019, there were 20 recorded “near miss” incidents involving aircraft and hailstorms. Though weather radars often help pilots avoid such threats, hail at cruising altitudes—above 30,000 feet—can be difficult to detect. While windscreens are strong enough to resist bird strikes, hail can still obscure visibility, making landings more challenging.

On June 9, 2024, an Austrian Airlines flight landed safely in Vienna after a severe hailstorm mostly stripped away the nose radome—the aerodynamic shell covering the front of the airplane—leaving the jet’s substructure exposed. The remainder of the skin was pocked with dents from hailstone impacts. The two windows directly in front of the pilots were heavily damaged but intact.

Record-breaking hailstones reported in Texas, Colorado, and Alabama have reached sizes of up to 16 cm in diameter. In Tripoli, Libya, hailstones nearly 18 cm across were recorded in 2020. Likewise, a hailstone measuring 16 cm (6.4 inches) across and weighing 590 g (1.3 lbs) was collected after a storm near Hondo, Texas, in April last year.

Research suggests that climate change may contribute to larger hailstone sizes; this may be the new normal. According to the US National Oceanic and Atmospheric Administration, an updraft of 103 km/h can produce hail the size of a golf ball, while an updraft 27 percent faster can create hailstones the size of a baseball.

Northern Illinois University Atmospheric Science Professor Victor Gensini published a study in the journal Climate and Atmospheric Science. He found, “the largest hailstones are found to increase by 15 percent to 75 percent, depending on greenhouse gas emissions.”

According to Julian Brimelow, a physical sciences specialist at Environment and Climate Change Canada, as the planet warms, areas prone to hailstorms may shift—potentially increasing hailstorm frequency in some regions. Canadian research suggests hailstorms will become more frequent in Australia and Europe, but decrease in East Asia and North America. The hailstorms are also expected to become more intense. In North America, hailstones may become larger despite the decreasing frequency.

akistan Meteorology Department Director General Mahr Sahibzad Khan says in Pakistan, hailstorms typically occur during March-April, the transitional period between winter and summer. “It is generally a phenomenon of the hilly areas of Kashmir, Khyber Pakhtunkhwa, Gilgit-Baltistan and the Potohar plateau, where unstable weather conditions and cold air masses are common. Plains have a lower incidence.”

A hailstorm system is generally spread over 5-10 km, he added. For last week’s storm in the federal capital, “the size of the hailstones was estimated to be of grapefruit size.” He noted that the grapefruit-sized hailstones were among the largest in recent memory.

To safeguard against the growing threat of intense hailstorms, vulnerable areas are adopting hail nets as a protective measure. These are often made from high-density polyethylene and installed over crops, vehicles, homes to intercept hailstones and prevent damage. By providing a barrier, they help protect lives, crops and property from the increasing risk of hailstorm-related destruction.

As hailstorms grow fiercer and more unpredictable in a warming world the cost of inaction rises. While forecasting remains a challenge, investing in resilient infrastructure and climate adaptation strategies is essential. The future may bring even bigger storms. How we prepare today will determine how well we weather them.

The writer is a senior staffer in Karachi