Concrete Jungles on Fire

On a sizzling afternoon in Lahore these days, the mercury does not just go up; it feels as though it is actively hunting you. The air is hot, the asphalt is sticky and the concrete buildings radiate heat like open oven doors. Go a few kilometers away from the city limits and walk into the agricultural belt of a rural area, you feel the temperature drops, noticeably. This is not a mirage or a trick of the weather; it is the urban heat island (UHI) effect – a new man-made environmental crisis that is turning the world’s fastest-growing cities into lethal heat traps.

Urban heat islands occur when urban areas experience notably higher temperatures than their surrounding rural regions due to human activities and the built environment. The phenomenon, once considered a local urban issue, has now emerged as a major climate concern in the world. Combined with surging climate change, urban heat islands are intensifying heatwaves, increasing energy consumption, worsening air pollution and posing a threat to public health across the world.

For developing countries such as Pakistan, where rapid urbanization and climate vulnerability are combined, the UHI effect is not just an abstract scientific concept; it is the difference between a livable pleasant day and a suffocating one. Major cities are becoming increasingly hotter, exposing millions of residents to hazardous temperatures and placing additional strain on already stressed infrastructure and resources.

To understand the UHI effect, we need to comprehend the language of surfaces. In a natural setting such as a forest or a grassland, solar energy is absorbed by plants and moisture. Much of that energy is used for evapotranspiration, the process by which water evaporates from leaves, cooling the air like a natural air conditioner. However, urban areas speak a different language: the language of asphalt, concrete, steel and brick. These materials are characterized by low albedo, meaning they do not reflect sunlight well, and high thermal mass, which stores heat. When the sun hits a dark roof or a paved road, the energy is not used for cooling; it is stored. It means throughout the day, the city acts as a battery for heat, and when the sun sets, the countryside cools rapidly, but the city slowly releases its stored energy. At night, while rural areas might be pleasant, the urban areas remain miserably hot. According to studies, globally, the UHI effect adds an average of 1°C to 3°C (1.8°F to 5.4°F) to city temperatures compared to surrounding rural areas. However, in dense, hyper-urbanized megacities, this difference can go up to 10°C or more on calm, clear nights.

There are three secondary factors that exacerbate the UHI effect and increase urban heating. The first one is anthropogenic heat, which means the environmental degradation caused by human activity rather than natural processes. It occurs when the waste heat from air conditioners, car engines and industrial machinery pumps thermal energy into the urban envelope. It is ironic that as cities get hotter, people use more air conditioners, which vent hot air onto the streets, making the outside even hotter. The second factor is the canyon geometry, which tells us how solar radiation is trapped, reflected and released within urban streets. Tall buildings and narrow streets in cities block wind and trap radiation, preventing the longwave radiation from escaping back to space and resulting in the temperature rise during daytime and nighttime. The third factor is the lack of permeable surfaces in urban areas, which prevents rainwater from soaking into the ground, eliminating the natural cooling effect of evaporation.

Climate change and urban heat islands are interconnected and reinforce one another. Climate change is increasing average temperatures worldwide. When these rising temperatures combine with the urban heat island effect, cities experience even more extreme heat, resulting in longer, more frequent and more intense heatwaves. To cope with these heat extremes, demand for air conditioning and cooling systems in cities spikes. Resultantly, electricity consumption increases leading to higher greenhouse gas emissions, especially in regions that rely on fossil fuels for power generation. This process, in return, reinforces climate change. In this way, this lethal environmental degradation cycle continues.

The combination of climate change and urban heat islands poses serious health risks such as heat exhaustion and heatstroke; increased mortality during extreme heat events; worsening of respiratory and cardiovascular diseases; and mental health stress associated with prolonged heat exposure. Low-income communities often suffer the most because they lack access to reliable cooling systems and adequate housing. Urban heat islands impact local water cycles as well by increasing evaporation rates and altering rainfall patterns. Higher temperatures also place additional pressure on water supplies during drought conditions.

Pakistan is among the countries most vulnerable to climate change. Rising average temperatures and more frequent extreme heat events amplify the urban heat island effect. During heatwaves, city residents face compounded risks because both global warming and urbanization contribute to higher temperatures. Rapid and unplanned urbanization over the past several decades has transformed cities such as Karachi, Lahore, Islamabad, Faisalabad, Peshawar, Multan and Rawalpindi. Population growth has fueled extensive construction, road expansion, industrial development and housing projects, often at the expense of trees, parks and agricultural land. Consequently, many Pakistani cities experience significantly higher temperatures than nearby rural areas. During summer months, densely populated urban areas can become heat traps where temperatures remain elevated throughout the day and night.

It goes without saying that without effective intervention, urban heat islands will continue to threaten public health, economic productivity and environmental sustainability. However, the problem is not insurmountable. There are ways that can help mitigate the urban heat island effect. First of all, there is need to expanding urban green spaces in urban areas, because planting trees and creating parks can significantly reduce temperatures through shade and evapotranspiration. Urban forests also absorb carbon dioxide and help in mitigating climate change. Vegetation-covered roofs and walls can also lessen building temperatures, improve insulation and enhance urban biodiversity. Additionally, using light-colored and reflective materials helps reduce heat absorption and lower surface temperatures. Sustainable urban planning such as designing cities with adequate green spaces, improved ventilation corridors and climate-resilient infrastructure can help minimize heat accumulation. There is pressing need to curtail fossil fuel use through renewable energy and encourage efficient public transportation to decrease both greenhouse gas emissions and waste heat generation.

Addressing the problem of urban heat islands requires coordinated action by governments, urban planners, businesses and communities. Governments should develop heat action plans, establish early warning systems and educate citizens about heat-related risks. Sustainable urban development requires a balance between economic growth and environmental protection. Strengthening environmental assessment laws, improving enforcement and integrating environmental considerations into urban planning can help create cities that are not only prosperous but also resilient, healthy and environmentally sustainable.

Ill-planned and unregulated urbanization together with economic aspirations has turned green spaces into concrete jungles, and now, these concrete jungles are on fire. Fixing this problem requires a radical rethinking of what a city is. However, the solution is not to abandon cities; it is to reinvent them. If we cannot stop urbanization, we can change the materials and geometry of cities. Addressing the issue of urban heat islands today will not only improve quality of life for millions of people but also strengthen the broader fight against climate change in Pakistan and around the world.