Urbanisation turns up the heat

Metropolitan Karachi is facing the brunt of an intensifying heatwave

Comparative vegetation cover of cities around the world. Image: supplied
Comparative vegetation cover of cities around the world. Image: supplied


 drive through Pakistan’s cities today reveals a stark reality: unsustainable urbanisation has transformed the metropolises into sweltering hotspots, where heat waves are intensifying. Densely packed, tall buildings, devoid of green spaces, have created urban heat islands that trap the sun’s radiation, turning cities into virtual furnaces.

Destruction of tree-lined landscapes and sacrificed farmland are compounding this crisis, leaving the citizens vulnerable to the intensifying heat waves. Fossil fuels, vehicles emitting greenhouse gases into the atmosphere and concrete-glass buildings trapping the atmospheric heat appear to be the new normal.

“The world experienced an average of 26 more days of extreme heat over the last 12 months. That would probably not have occurred without climate change,” says a recent report published by the Red Cross and Red Crescent Climate Centre, the World Weather Attribution scientific network and the nonprofit research organisation Climate Central.

The report says that, over the last 12 months, some 6.3 billion people — roughly 80 per cent of the global population - experienced at least 31 days of extreme heat. 76 extreme heatwaves were registered in 90 countries on every continent except Antarctica.

Deforestation and urbanisation interact with global warming to cause more hot days or increase the severity of the heat waves. Deforestation removes the shade and the cooling effect on the surrounding wind and the amount of heat absorbed by earth further increases the temperature. This warming is symbolic of all urban centres where tall, concrete-laden structures raise the temperatures by 1-3°C, more than that of the surrounding areas. This is called the urban heat island effect. Slower heat release at night keeps the area hotter compared to the suburban or rural parts.

The urban canyon effect retards the circulation of air due to the close construction of the buildings enclosing narrow lanes and alleys. This disruption of the air flow in its immediate vicinity as well as that of the larger regional wind fields increases the UHI effect and slows down natural cooling. Unplanned urban centres in Karachi, Lahore, Peshawar, Islamabad, Multan and Faisalabad trap more heat, allowing their citizens little respite against the rising mercury.

The quality of construction in Karachi is a serious concern. Many buildings manifest inadequate natural light and ventilation. There are water shortages and long power outages.

According to a study by the Karachi Urban Lab, since 1960 nighttime temperatures in Karachi have risen by about 2.4°C. The daytime temperatures have gone up by 1.6°C. Tormented by sweltering heat and humidity, some Karachiites find relief in the evenings due to the sea breeze. But for those living and working downtown there is no such relief.

In 2018 and 2022 unusually high temperatures in March and May caused many deaths. In 2015, more than 1,000 people perished in Karachi. The excruciating heat hurts animals and humans alike. It is particularly hard on children and older people. It raises the health risks associated with diabetes, cardiovascular diseases and respiratory illnesses. It can also cause acute kidney injury.

The Pakistan Meteorological Department has warned of three heatwaves from May to mid-June. The forecast prompted the Sindh government to postpone intermediate examinations across the province for a week. The Provincial Disaster Management Authority and partner humanitarian organisations set up 1,321 heat stabilisation camps across various parts of the province. The sick were taken to heat stroke centres at nearby hospitals. As many as 3,913 patients were admitted. 3,889 of them were discharged while 24 remained hospitalised. Besides 144 livestock were lost to the heatwave. Electronic and social media were engaged to spread awareness about the impending heat waves and the precautions that needed to be taken.

“Ironically, the only dense green canopies left in the metropolis are in the graveyards.”

Over the last 50 years, the average temperature of Karachi has risen by 2.5°C. It now stands at 28.5°C. Shahbaz Azim, 55, has spent most of his life in the megapolis. He says the city has grown significantly hotter during his lifetime. “I have lived almost all my life in the heart of the city. It has now grown more humid and hot. Sometimes even sitting under a fan is not enough,” he says.

“[In past] shaded waiting areas for public transport and people selling iced water, lemonade etc were a common sight. There were many evening schools. Only rarely did we hear aou somebody who had suffered a heatstroke,” recalls Azim.

Tayyaba, Azim’s wife, says certain dietary changes were made in summers. “Onions and vinegar, curds or salted lassi were essential additions during hot days,” she says. Moringa gravy was another addition to the menu. “Tamarind is a natural antidote to malaria and an essential part of South Indian or Western African cuisines.”

The duration and frequency of heatwaves has increased over the years, says the Sindh chief meteorologist, Sardar Sarfraz. “The heat waves were not so common until 1990,” he says. “The climate is getting warmer. Some regions now face rapid increases in average annual temperature,” he explains.

“Cold nights are becoming less frequent. The summers have prolonged and winters have become shorter,” says Sarfraz.

Pakistan is a temperate-zone country with a dry and hot climate. This has allowed people to develop techniques, materials and building designs to retard heat and provide robust ventilation. However, modern, cluttered apartments don’t allow for wind-catching. “This issue gets further complicated due to the removal of local trees which have been replaced mostly with exotic palm trees that do not provide canopy cover. Trees are not only carbon sinks but also lower the temperatures,” says environmentalist Rafi-ul Haq. He says the forest cover has shrunk drastically.

Green zones with local species must be developed around the urban sprawl to offset the UHI effect. They are central to any heat mitigation strategies, irrespective of size,” says Haq.

“In Karachi, the cooler parts are either the suburbs, open spaces near the airport, or areas close to the sea,” he says. “Ironically, the only dense green canopies left in the metropolis are in the graveyards,” says Rafi.

He worries that the Malir Expressway connecting localities on M9 with KPT Interchange could destroy 4,300 acres of green space. “This will complicate the already complex heat island profile of the city exposing it to more heatwaves. The consequent commercial and real estate development will wipe out the green zone from Malir-Korangi and Shah Faisal, that once used to supply vegetables and fruits to the city. The Expressway could also obstruct rainwater discharge,” he says.

There has never been sustained policy enforcement to support artificial forests, save for Changa Manga. The Billion Trees Tsunami programme has lost steam. It is imperative to address this pressing issue through concerted efforts to mitigate the impact of urbanisation on rising temperatures and to protect the health and well-being of urban populations.

The contributor works for The News International

Urbanisation turns up the heat