Heat Waves and High Rises: Navigating Urban Heat Islands in Modern Cities

Imagine walking in a park on a hot day, enjoying the shade under tall trees. Now, think about walking on busy city streets, feeling the heat getting more intense with each passing block. Have you ever wondered why parks feel cooler than city streets?

This temperature difference you experience is the phenomenon known as Urban Heat Island (UHI). UHI is characterized by significantly elevated temperatures in a city center relative to the surrounding urban fringe or rural areas.?

Due to rapid urbanization, nowadays more land is transforming into concrete jungles, where natural landscapes such as bio reserve areas, farmlands, and public parks are replaced by high-rise structures and dense road networks. This shift results in a widespread reliance on asphalt and concrete which are high heat-absorbing materials. Also, the towering structures hinder the movement of winds and capture heat.?

This story is not new. You might have heard your grandparents mentioning the escalating temperatures that they've observed over the past few decades.

Since the last 50 years, India has been experiencing more frequent, longer, and hotter heat waves. Between June and August 2023, 11 states/UTs encountered temperatures approximately three times higher than usual, a consequence of the climate crisis, according to Climate Central's Climate Shift Index.

Furthermore, a study conducted on the city of Thiruvananthapuram in the Indian peninsula revealed a significant variation in cooling rates—a measure of how quickly an area's temperature drops over time—between urban and rural areas, which show 1.5°C/h and 3.4°C/h, respectively.

What's behind the scenes in shaping the Urban Heat Island (UHI) effect??

As you walk down urban streets the glass buildings that you see all around, gain more heat and thus increase the cooling demand of the interior spaces. The conventional cooling methods in turn add heat to the environment, creating a vicious cycle of cooling .

The UHI effect can be attributed to various factors– intrinsic city parameters such as building size, geometry, density, material properties, and population- and external factors such as topography, regional climate, and meteorological conditions.

Asphalt, the most common construction material for roads, acts as a heat magnet. Its dark color readily absorbs solar radiation, making surface temperatures significantly higher than the surrounding air. Studies have shown asphalt roads can reach up to 50°C (122°F) on a hot day when the air temperature is 25°C (77°F).

Seasonal temperature changes also affect the Urban Heat Island (UHI) effect.?

In summer, dryness of air worsens UHI as concrete heats up, making cities up to 5°C warmer. But it's not all bad news! Winter rains and increased spring vegetation, help counteract UHI. Rain adds humidity, limiting evaporation, and more plants provide shade, reducing UHI by 2-3°C. These seasonal factors show how weather and urban features interact to influence local temperatures.

Our urbanizing cities, marked by glass buildings and extensive road networks, are now recognized as major contributors to global climate change. The rising urban temperatures bring challenges like increased demand for cooling, affecting comfort and livability. By 2043, India's Cooling Demand is projected to be 11 times that of 2023, emphasizing the need for efficient and sustainable cooling solutions .

Are there any steps individuals and communities can take to mitigate the impact of Urban Heat Islands?