What lessons can Karachi learn from big cities to tackle heat?

SCORES of people died in Karachi due to the recent heatwave, and there seems no end to it. Heatwave in Karachi can be compared to the 1,300 deaths during recent Haj due to the excessive heat. The Saudi health minister said that the deaths occurred among pilgrims who walked long distance under scorching sun, without water and shade facilities.

In Karachi, the victims were not able to access the heat shelters, as probable none exist, and this caused their deaths.

According to Ollie Jay, a professor of heat and health at the University of Sydney in Australia, heat kills in three ways. First is the heatstroke. When inner body temperature gets too hot, the body redirects blood flow toward the skin to cool down. But that diverts blood and oxygen away from the stomach and intestines, and can allow toxins normally confined to the gut area to leak into circulation.

That sets off a cascade of effects, like blotting around the body and multiple organ failure and, ultimately, death. The bigger killer in heat is the strain on the heart, especially for people who have cardiovascular disease. It again starts with blood rushing to the skin to help shed core heat. That causes blood pressure to drop. The heart responds by trying to pump more blood to keep a person from passing out. Heart is forced to do a lot more work than it usually does. For someone with a heart condition, the heart function can cave in and the person will die.

‘Cooling centres’, tree plantation along streets and painting concrete surfaces white are steps taken world over to fight heatwaves

Another way is dehydration. As people sweat, they lose liquids to a point that can severely stress kidneys. Many people may not realise the danger. Dehydration can progress into shock, causing organs to shut down from lack of blood, oxygen and nutrients, leading to seizures and death. Dehydration can be very dangerous and even deadly for everyone if it gets bad enough. It is especially dangerous for those with medical conditions and on certain medications. Dehydration also reduces blood flow and magnifies cardiac problems.

Heat also affects the brain. It can cause a person to have confusion, and the person suffering from the heat is unlikely to recognise it. And it becomes a bigger problem as people age.

Certain medications may increase the severity of heat. Medications can affect a person’s perception of heat and interfere with internal thermostat. They can alter the body’s ability to redirect blood flow to the skin, a key way that it cools itself.

Antidepressants may increase sweating, increasing the risk of dehydration. Tricyclic antidepressants, may decrease sweating, making it harder to cool off. Antipsychotics may impair sweating and alter the body’s internal thermostat.

Anticholinergic drugs, a large category of medications commonly used to treat an array of conditions such as urinary incontinence, overactive bladder, allergies, and Parkinson’s disease, may interfere with sweating and the body’s internal thermostat. They may also reduce blood flow to the skin. Patients with heart disease may be prescribed multiple medicines, including diuretics and ACE inhibitors. Such drugs can cause dehydration, affect kidney function, and limit the body’s ability to redirect blood flow.

Dehydration can increase the blood levels of some medications. Some diabetes medications, including insulin, can lose their effectiveness in hot weather.

A major life-threatening consequence of some medications is that, they cause weakness, agitation, confusion, and impaired perception of heat. And all these symptoms will lead to the death.

Heat management for Karachi

Karachi can learn from what other cities have done to tackle heat. Many major cities, like New York, Los Angeles, Boston, Chicago, Portland, Seattle and Toronto have cooling centres, an air-conditioned public or private place where people can cool off.

In Bangkok, there are informal cooling centres, meaning that the large air-conditioned shopping malls which double as cooling centres. In Bangkok, there are many such malls.

Phoenix has mobile medical teams, which provide cooling facilities and deliver lifesaving IV hydration in extreme heat. In Miami, the Miami-Dade County staff goes out and distribute cold water bottles and other supplies to people in distress, and help them to manage high temperatures. When the heat become excessive, the county staff provides cooling towels, helps coordinate water donations, hands out maps of where cooling sites are located, and even offers transportation.

Many cities have prepared heat maps, indicating locations that are very hot, and very vulnerable from a human perspective. Once identified, the municipal staff goes out and paints the hottest streets with a special cool pavement coating. The paint reflects the sun heat, rather than absorbing it.

Karachi has almost zero coverage of green space. A person standing at the Empress Market, Saddar, and a victim of heatstroke, is exposed to excessive heat from the engines of cars and buses, and will have nowhere to go to access green shades.

Installing significant green spaces, planting more trees along streets, and painting concrete surfaces white are just a few of the simple adjustments Karachi can take.

New York has a major programme of painting the roof white with white silicone reflective paint. New York’s Coolroofs programme has painted over 10 million square feet of roof over the last 10 years. Painting parking lots white also makes a huge difference to heat reduction.

A 2022 study from China exploring the cooling effects of urban parks concluded that parks heat up more slowly than urban regions during the day, and that green public spaces containing water had a better cooling effect both inside the park and in the surrounding area.

The city of Medellín in Colombia has demonstrated the cooling power of trees. Unplanned development had eliminated green spaces and caused temperatures to rise 6°C above average. To combat this, between 2016 and 2019, 36 corridors of trees and other vegetation were planted along major roads and waterways, with vulnerable neighbourhoods prioritised. Covering more than 36 hectares, these areas have already seen temperature reductions of up to 4°C.

Paris has an excellent interlinked network of cool islands where people can seek relief. These islands are linked by naturally cool tree-covered walkways.

When fossil fuel is burnt in power plants or in vehicles, carbon dioxide is produced. This invisible gas builds up in the atmosphere and traps the Sun’s warmth near the Earth’s surface. As the people keep on burning fossil fuel, the carbon dioxide adds a little bit more to the temperature. As temperatures rise, the planet becomes hot, leading to extreme heat.

Heat is dangerous. When extreme heat is combined with high humidity, the human health risks multiply. Warming makes ocean water expand, and this leads to sea level rise. Rising sea levels threaten to displace as many as two billion people by 2100.

Since vehicles have increased multi-fold in cities, the transportation has become a major source of extreme heat.

Many studies have shown that it is nearly impossible to reduce heatwaves, if the transportation sector is not decarbonised, meaning reducing vehicles, switching to electric vehicles, and having efficient transit transportation. Can Karachi achieve that target?

To the good luck of Sindh, incumbent Chief Secretary Asif Hyder Shah was formerly the federal secretary of the ministry of climate change and environmental coordination. With that experience he can lead the programme of providing facilities to manage the heatwaves in Karachi.

The writer earned his master’s degree in environmental engineering from the Asian Institute of Technology, Bangkok, in 1975.

Published in Dawn, July 22nd, 2024