Decoded: Urban heat islands and how they are formed

In the face of the rising heatwave across India, NASA has been monitoring the temperatures from space using its space satellite instrument called Ecosystem Spaceborne Thermal Radiometer Experiment on Space Station, or ECOSTRESS in short. This instrument has observed that urban areas in and around Delhi have recorded significantly high temperatures in comparison to their surrounding rural areas. This strange phenomenon has been named urban heat island. Are you also wondering what this means? Well, let us find out together.  

Are city structures the culprit? 
All of you, who live in concrete jungles, have experienced frequent rise in temperatures, sudden heatwaves and many uncalled-for weather conditions. When an urban area   experiences much warmer temperatures that its surrounding rural areas, it is known as urban island. This term was first coined by the US Environmental Protection Agency (EPA) in 1958 when a meteorologist named Manley was conducting his investigation on change in snowfall patterns in rural and urban regions.  

But, what’s the culprit behind this phenomenon, any guess? Well, the remarkable is dissimilarity in temperatures between a city and its outlying areas is, in many cases, the result of their infrastructural differences. While natural landscapes such as forests and water bodies absorb the heat, urban structures such as roads, bridges, and buildings first absorb the heat but then end up re-emitting it.  

Factors responsible for the formation of urban heat islands 
Apart from urban structures, there are various other factors responsible for the formation of urban heat islands. Read on to know more. 

Less number of natural landscapes: All of us know that the reduced number of natural landscapes, such as trees, vegetation, and water bodies in the cities tend to make them high-temperature pockets. As a result of this, there’s absence of natural shade, cooler air, and evaporation of surface water. To add to these, urban structures like roofs, sidewalks, buildings, parking lots and streets also provide minimal shade, further contributing to hotter temperatures. 

Human activities: Apart from everyday pollution, vehicles, air-conditioning units, residential as well as industrial activities—all these contribute to the generation of excessive heat in the urban areas. This heat, in turn, is unable to dissipate, thanks to lack of natural structures. Eventually, this leads to the formation of urban heat islands.   

Urban building materials: Building materials such as asphalt, brick, steel, etc. are much more in use in the urban areas than in the rural ones. These not only absorb less of the heat but also emit more. In fact, contrary to common beliefs, urban materials release heat at a slower rate, which results in building up of the heat throughout the day. The random urban planning, that often doesn’t take into consideration the dimensions, spacing and airflow necessary to let the city breathe also affects the temperatures further. Evidently, this leads to pronounced heat after sundown, rather than the expected cooling down of temperatures.