Sea breeze is the lifeline for Karachi. It helps keep the city’s temperature down and blows away emissions from hundreds of thousands of vehicles, factory chimneys and the daily burning of hundreds of tonnes of hydrocarbons. When the sea breeze stops, the coastal city starts heating up, causing a deadly situation for people and other living creatures on the ground.

Pakistan Meteorological Department officials believe that the suspension of sea breeze has been occurring more frequently since 2015, when Karachi experienced one of its worst heat waves in decades, resulting in the deaths of over 1,500 people. The rising temperature of the Arabian Sea is leading to the frequent formation of low-pressure areas, which cut off the sea breeze to Karachi. Low-pressure areas during the monsoon season over Rajasthan also cause a reversal of the sea breeze, resulting in agonising heat waves in the coastal city.

In the absence of the sea breeze, the moisture in the air heats up. Although the daytime temperature remains between 40 and 42 degrees Celsius when a heat wave is predicted, the heat index, or feels-like temperature, often reaches 50-55 degrees Celsius. This is unbearable for humans, animals and birds. Those working under the sun or living in concrete structures without electricity are especially vulnerable to heat stroke, sometimes leading to death.

The Urban Heat Island Effect exacerbates the situation in the port city when the sea breeze is missing. Without this cooling factor, the city becomes hot even at night. The constant heat becomes unbearable, particularly for those living in areas with high load shedding, streets without trees for shade and limited access to water. Concrete structures absorb heat during the day and release it at night, but in Karachi, when sea breeze is cut off, the heat remains trapped, keeping the city hot and unbearable.

The same phenomenon occurred on June 23, when air containing extremely high moisture started heating up in Karachi as the temperature soared to 40 degrees Celsius while the sea breeze was cut off due to a low-pressure area in the Arabian Sea near the Indian coast of Gujarat, raising the heat index in Karachi to above 50 degrees Celsius.

“Extremely high moisture content from the Arabian Sea had been pumped into the air over Karachi on the night between June 22 and June 23. Suddenly, in the morning, the sea breeze stopped. With no air from the sea to clear the moisture from Karachi’s skies, it started heating up. The temperatures rose to 40 degrees Celsius, making people feel as if they were inside a heated pressure cooker,” Dr Ghulam Rasool, the former director general of Pakistan Meteorological Department, told The News on Sunday.

Hundreds of people have reportedly died due to heat stroke during the ongoing heatwave that gripped Karachi since Sunday, June 23. Some welfare organisations claim the death toll due to the heatwave is as high as 100.

Health experts say more than 90 per cent of people who died from heat stroke never managed to reach hospitals. They died on the streets, at home or on the way to a health facility.

However, the Health Department says that only 45 people have died due to heat stroke and related causes based on data from four leading public health facilities. Experts say more than 90 per cent of the people who died from heat stroke never managed to reach hospitals. They either died on the streets, at home or on the way to a health facility.

Dr Rasool, now an advisor at the China-Pakistan Joint Research Centre at Quaid-i-Azam University, Islamabad, says that recent heat wave in Karachi has not been as severe as the one witnessed in 2015, it has been longer in duration and caused extreme agony to people in the port city for an entire week.

“This time, the temperature rose to a maximum of 41-42 degrees Celsius, unlike in 2015 when the maximum temperature rose to 45-46 degrees Celsius. But this year, the duration was longer compared to the 2015 heatwave,” he said.

Dr Rasool warns that the frequency of heat waves is expected to rise in the years to come. He advises people and authorities to focus on mitigation and adaptation to changing climate conditions.

Sindh’s chief meteorologist, Dr Sardar Sarfraz, sats the heat wave that started on June 22-23 was caused by a low-pressure area in the Arabian Sea. He says it stopped the sea breeze towards Karachi, causing moisture suspended in the air over the city to heat up, leading to suffocation and heat exhaustion for people on the roads and those without electricity at home.

He says that as the sea breeze was cut off and humidity remained over 70-80 per cent, the heat index, or the feel-like temperature, rose beyond 50 degrees Celsius. This was higher than many people could bear, especially those with compromised immunity, the weak and elderly, and those working under the sun.

“We are hearing of deaths due to heat stroke. Most of the deaths occurred on the roads, among people who live on the streets, those who work under the sun and people who were inside their homes but had no electricity to cool them off,” Sardar Sarfraz says.

Dr Sarfraz also blames the Urban Heat Island Effect for the severity of the heat waves in Karachi, saying concrete structures trap heat during the day and release it at night. When there is no sea breeze, there is no way to cool the city. “We had the highest ever minimum temperature of July recorded this month because there was no sea breeze at night,” he says.

Health experts say heat stroke is a health emergency that can cause death within minutes or in a few hours, depending on factors like age, health status, environmental conditions and the speed and effectiveness of medical intervention.

“A heat stroke can develop rapidly, often within minutes, especially during extreme heat conditions or vigorous physical activity. Initial symptoms may include high body temperature (usually above 40°C), altered mental state or behaviour (such as confusion, agitation, slurred speech, irritability, delirium, seizures or coma), nausea and vomiting, flushed skin, rapid breathing and a racing heart rate,” says Dr Khurram Nizami, a medical specialist.

According to Dr Nizami, without prompt treatment, the body’s temperature continues to rise, leading to a severe heat stroke. During this stage, the body’s internal systems begin to fail. This includes the central nervous system and organs such as the liver, kidneys and muscles.

“In severe cases, a heat stroke can cause life-threatening damage within a few minutes. Rapid progression can lead to multiple organ failure, brain damage and death if the body temperature is not reduced quickly. Quick action, such as moving the person to a cooler environment, initiating cooling measures (like ice packs or cool water immersion) and seeking emergency medical care, can significantly improve the chances of survival,” he says.

The contributor is an investigative reporter, currently covering health, science, environment and water issues for The News International