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Karachi, an 'urban heat island'

Updated June 25, 2015

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In the middle of a heat wave in Karachi, ice is a precious commodity. — Photo by author
In the middle of a heat wave in Karachi, ice is a precious commodity. — Photo by author

As the first monsoon winds blow from the Arabian Sea to bring relief to a city where 950 people have been reportedly killed in a heat wave this June, climatologist Qamaruz Zaman Chaudhry terms the scorching heat in Karachi an “urban heat island” phenomenon.

When the temperature is 45 degrees Celsius but it feels like 50, that is because hot air has been trapped and cannot escape, he explains. "The city is like a furnace that captures the heat without letting it escape.”

He said these same temperatures, even higher, have often been reported from other parts of Sindh, but that has not killed people like it has in Karachi this year because there is room for hot air to circulate and dissipate.

Ghulam Rasul, Director General of Pakistan Meteorological Department, explained to thethirdpole.net that the situation had become worse due to a low pressure area over the Arabian Sea. So a hot wind was blowing from the land to the sea instead of the other way round.

"In summer, the cool wind blows from the sea to land and in winter it is the other way round. This keeps the temperatures in Karachi, both in winter and summer months, reduced by nearly 15 degrees Celsius. The sea breeze is an important temperature moderator." That was missing this June.

While heatwaves have been observed in Karachi in the past, Rasul said this time the duration was longer. "In the past, it would last for a maximum of two days, but this time it continued for five to six days."

The scorching heat has taken a toll on human life, with over 800 deaths reported officially. Thousands more are being treated at various hospitals – both government-run and private ones – with many in serious condition. The city of an estimated 20 million has its mortuaries filled to capacity and not enough gravediggers.

Asked if this is a result of climate change, Chaudhry – who is also the UN Secretary General’s Special Advisor for Asia with the World Meteorological Organisation and the Asian Development Bank; plus a specialist in climate change and disaster risk management – responded in the affirmative and said he had little doubt that such events will increase in frequency in future.

That is what the scientists at the Intergovernmental Panel on Climate Change have been forecasting too. However, Arif Ahmed Khan, secretary in Pakistan’s Ministry of Climate Change, was more cautious.

"It is perhaps too early to relate such events unequivocally to the changing climate on earth, he told thethirdpole.net. "However, bizarre occurrences like the heatwave in Karachi and neighbouring Mumbai’s heavy rainfall can be seen as precursors to a change in the pattern in which local climate systems are responding to the planet’s unease with its atmosphere."

Concurring with Chaudhry about the heat island effect, Khan said: "This can happen when a massive urban settlement is exposed to high temperatures for an extended time." However, he added, Karachi’s heat may well have been exacerbated by humidity.

Others say long hours of power outages (and which have also led to water shortages) in the holy month of fasting – Ramazan – have added significantly to the problem.

Living with heatwaves

If heatwaves are going to get more frequent, how does one live with them? Farhan Anwar, urban planner and environmentalist, says there are a number of ways.

"It is time to revisit how buildings are designed and the material used."

High rises that have closed natural wind tunnels and traffic fumes have intensified the problem. Anwar suggested looking at India’s green building standards and reviving local architectural traditions.

"If they can do it, why not us? Why does our conversation around sustainable development end at workshops and seminars?"

Another way of absorbing the heat is to have streams flowing across the city, suggested Anwar. "We have the Nehre-i-Khayyam running across the town and we have natural drainage channels (now transporting sewage) which can be revived and the water treated; or you can build artificial ones."

He also suggested a low-cost method of "greening" roofs by covering them with plants and shrubs which can help in reducing the amount of energy needed to keep a building warm in winter or cool in summer. "It is mandatory in France to have either roof gardens or solar panels," he held.

Green roofs are popular in Germany and Australia too. Toronto, in Canada, passed a law in 2009 making it mandatory for industrial and residential buildings to adopt green roofs. But such efforts, Anwar said, can only bear fruit if done on a mass scale.

He also suggested temperature mapping of the city be made mandatory. "With surface temperature mapping, you would be able to immediately detect the hotspots and taking a multi-layered GIS approach be able to find out if it is due to population density, traffic or some other reasons. Armed with this information, planners would be better able to tackle the heat and rising temperatures."

Rafiul Haq, a member of the International Union for Conservation of Nature for ecosystem management, believes there will be some respite by planting and nurturing trees – which he terms "lungs of the city".

"The concrete buildings have compromised the city’s breathing and we need to grow trees to revive it."

According to Haq, trees are natural air conditioners. When the leaves transpire, they provide a cooling effect to the atmosphere. However, he said it was important to know what to grow as wrong plants can prove damaging.

A decade or so back, the city government planted some 2.5 million Corynocarpus trees in a bid to counter the city’s environmental pollution. Haq said it was a poor choice as research has shown this plant to be a major cause of pulmonary allergies. He said to understand which plants work best for a city, it was important to understand the relationship of that city to the weather systems.

"Karachi needs neem (Azadirachta indica) trees which will be able to withstand the harsh climate that Karachi has had since the 1980s. It would be perfect to start planting the tree when the monsoonal plantation season begins from next month (July 15 to September 15) onwards," he recommended, but warned that unlike Corynocarpus, the latter was a slow growing tree which may take a good three years before it begins to make its presence felt.

"You’re playing with perennials so you will need to be patient," he added.

On June 24, the meteorological office forecast that Karachi’s heatwave was at an end and it would rain soon. While the drop in temperature will bring some relief, the showers will be weak.

Seeding rain

The heatwave and the resulting deaths have prompted the government to mull over ways to induce artificial rain.

Chaudhry said the cloud seeding technology has been employed in the past – "in Tharparkar in 2000 when the region faced severe drought. But to be able to induce rain, the clouds have to be mature enough".

Renowned scientist and Pakistan’s former science and technology minister Attaur Rahman said the process of cloud seeding whereby silver iodide, potassium iodide or dry ice sprayed on clouds by airplanes, triggering rainfall, was a well-researched process. "It has been used over the last several decades with some success and there are no serious health or environmental hazards associated with it."

This article was originally published on The Third Pole and has been reproduced with permission.