It’s 8 PM on a hot and still June night in Karachi. Sweat trickles down your forehead as the fan does little more than shoot jets of hot air at you. You step outside your apartment expecting a cool breeze – instead, the air hits you like a blow dryer. The sun has long set below the horizon, but its presence lingers in the heat radiating from every surface.
Everything around you is scorching hot. A cyclist wipes his forehead at a traffic signal, and a nearby shopkeeper fans himself with a newspaper. Frustrated, you call your cousin back in rural Sindh, inquiring about the weather there. Expecting worse due to their village being beyond the reach of the cool sea breezes, you are taken aback upon hearing that your whole family is curled up in a blanket. Why such a huge temperature difference?
“No fan, no shade—just sweat and headaches,” complains Rafiq, a laborer.
Welcome to the world of Urban Heat Island – a cruel reality for billions dwelling in congested, poorly-planned urban agglomerations like Karachi. UHI refers to the stark temperature difference between urban and rural areas, primarily due to human activity, excessive construction, and a lack of vegetation and bare soil. In cities, heat is trapped by asphalt pavements, cement buildings, high-rise buildings, and other infrastructure. And even when the sun sets, that heat doesn’t leave – it radiates back into the air throughout the night.
The Toll of Karachi’s Heat
Karachi, Pakistan’s commercial hub, main port, and largest city, is turning into a concrete jungle at an alarming rate. Satellite thermal imagery from NASA’s Landsat program and research, such as Sajjad et al. (2015) shows worrying trends. The UHI effect causes spiraling average surface temperatures throughout the city, with some dense neighborhoods like Orangi town reporting night-time temperatures that are 7°C to 9°C higher than in the unpaved rural outskirts.
While these temperature spikes may seem like an urban nuisance, they’re far more dangerous than most realize. The effects aren’t just sweaty t-shirts and sleepless nights – they’re often fatal. Karachi’s urban heat disproportionately affects the poor.
Impoverished residents living in squatter settlements often have poorly-ventilated homes without access to air conditioning, and often even electricity. After 12 hours of back-breaking manual labor on the streets under the scorching sun, they suffer through long, restless nights, a big test of their patience and resilience, as even the dark refuses to cool.
“I’m on duty 12 hours a night, sweating in my uniform while others sleep in AC rooms,” says Kamran, a security guard outside an apartment complex.
In 2015, a devastating heatwave in Karachi killed over 1000 people in just three days. Hospitals were overwhelmed, graveyards ran out of space, and power outages marred the city, turning it into a furnace. Many of those who died lived in the most heat-vulnerable zones—densely built squatter settlements with narrow, encroached streets allowing for little wind to flow, no trees or bare soil, and fully paved asphalt streets that absorb more heat than they reflect.
What’s Baking the City?
Karachi is dominated by concrete, steel, and asphalt. Unlike natural surfaces like grass or soil, these materials absorb a lot of heat during the day, slowly releasing their stored energy well into the night. Add to that the heat expelled by air conditioners, exhaust fumes, and factories, and you’ve got a city that bakes itself from the inside.
Vegetation, which naturally cools the air by providing shade and through transpiration, is in scarcity. Decades of haphazard development have replaced green spaces with residential colonies, roads, shopping plazas, and commercial buildings. In many neighborhoods, trees are cut during road-widening as well as building infrastructure for public transport, often without any replanting.
Bare soil, once found on the outskirts or in residential gardens, has been buried under concrete. While this may reduce dust pollution, it also eliminates natural cooling systems that could otherwise mitigate the UHI effect.
Karachi needs Small Fixes!
While the problem is critical, solutions are not so complicated. Some are surprisingly simple.
Planting the Right Trees in the Right Places
Urban forestry and median strip plantations can significantly reduce local temperatures. A study by UCLA researchers (De Guzman et al.) found that expanding tree cover and using reflective surfaces could reduce heat‑related medical visits in LA by close to 70%. Cities like Los Angeles have launched huge urban afforestation programs targeting backward neighborhoods. Karachi can follow their footsteps while prioritizing native, drought-resistant tree species.
Neem and Peepal are fast-growing and develop large canopies, providing shade while also being able to withstand the harsh, hot, and dry weather of Karachi. For parks and green spaces, trees like Gul Mohr and Amaltas would not only help with cooling but also add to the scenic beauty through their flowers and fruits.
Pavement and Permeable Surfaces
Depaving means taking out excess concrete or asphalt and replacing it with natural ground—like soil, grass, or surfaces that let water pass through. Hard surfaces like asphalt soak up heat throughout the day and slowly release it at night, making cities warmer even after sunset. Meanwhile, depaved areas (soil, grass, vegetation) absorb less heat and cool the surroundings through evapotranspiration. Natural ground also soaks up rainwater, reducing urban flooding.
A notable case is the Cheonggyecheon Stream Restoration in Seoul, South Korea. A 5.8 km highway was replaced by green spaces and a stream, which resulted in an average land surface temperature (LST) decrease of ~7 °C along the former highway corridor compared to surrounding built-up urban zones
Cool Roofs and Reflective Materials
Buildings can be painted with white or reflective coatings to reduce heat absorption. Ahmedabad, India, launched a successful “cool roof” initiative that saw average surface temperatures plummet by as much as 5°C. Karachi’s squatter settlements, where afforestation could be challenging due to high population density, could benefit tremendously from such low-cost adaptations.
As climate change worsens, cities like Karachi face more than discomfort—they face serious health risks. In overcrowded, poorly planned areas, extreme heat can be deadly, especially for children, the elderly, and the sick. The solution isn’t complex: plant more trees, reduce concrete, and cool rooftops. What’s lacking is commitment from city officials and citizens alike.
References:
- De Guzman, V., et al. (2024). City trees save lives: How urban greening and reflective surfaces reduce heat-related illnesses in Los Angeles.https://www.wired.com/story/city-trees-save-lives
- Hussain Sajjad, S., et al. (2015). Urban Heat Island intensity and its impact on the microclimate of Karachi. Journal of Basic and Applied Sciences. https://www.sceintific-array.org/index.php/jbas/article/view/1281
- National Disaster Management Authority. (2015). Pakistan heatwave report – June 2015. https://en.wikipedia.org/wiki/2015_Pakistan_heat_wave
- NRDC. (2023). India’s Ahmedabad honored for life-saving heat action and cool roof plans. Natural Resources Defense Council. https://www.nrdc.org/press-releases/indias-ahmedabad-honored-life-saving-heat-action-and-cool-roofs-plans
- Reuters. (2025, March 10). Indian slums get cool roofs to combat extreme heat. https://www.reuters.com/world/india/indian-slums-get-cool-roofs-combat-extreme-heat-2025-03-10/
- Sharma, R., & Bhatnagar, A. (2020). Combating climate change-induced heat stress: Assessing cool roofs and their impact on indoor temperatures of urban slum households in Ahmedabad. https://www.researchgate.net/publication/340017377_Combating_Climate_Change induced_Heat_Stress_Assessing_Cool_Roofs_and_Its_Impact_on_the_Indoor_Ambient_Temperature_of_the_Households_in_the_Urban_Slums_of_Ahmedabad
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