It’s a well-known fact that today more than half of world’s population lives in cities (urban areas). According to some reports, cities are home to 55% of the world’s population. This number is increasing, and every year cities welcome 67 million new residents, 90% of whom are moving to cities in developing countries. By 2030, almost 60% of the world’s population is expected to live in urban areas.
On the other hand, India is still a village economy with nearly 2/3rd of the population living in villages. But that’s not going to remain the same in the coming years as urbanisation is picking up pace and according to some experts more than half the population will live in urban areas in next two decades.
People migrate to cities due to many reasons, the main being search of opportunities and better standard of living. Though the Covid-19 outbreak might have changed the outlook of the people about migration and hope of better standard of living in cities but that change is temporary and the mindset is going to get back to back normalcy once the threat of pandemic disappears.
But the big question is – are cities a better place to live in?
According to IPCC’s Sixth Assessment Report, Climate Change 2021: The Physical Science Basis, cities and their inhabitants are highly vulnerable to weather and climate extremes, particularly heatwaves, because urban areas already are local hotspots. Cities are generally warmer – up to several degrees Celsius at night – than their surroundings. This warming effect, called the urban heat island, occurs because cities both receive and retain more heat than the surrounding countryside areas and because natural cooling processes are weakened in cities compared to rural areas.
Why cities create heat islands?
There are three main factors that contribute to amplify the warming of urban areas. One of the most important factors that contribute to urban heat island is the urban geometry, which depends on the number of buildings, their size and their proximity. Tall buildings close to each other absorb and store heat and also reduce natural ventilation. Human activities, which are very concentrated in cities, also directly warm the atmosphere locally, due to heat released from domestic and industrial heating or cooling systems, running engines, and other sources. Finally, urban warming also results directly from the heat-retaining properties of the materials that make up cities, including concrete buildings, asphalt (and concrete) roadways, and dark rooftops. These materials are very good at absorbing and retaining heat, and then re-emitting that heat at night.
Vanishing parks & water bodies
The problem of urban heat island is multiplied by vanishing parks, gardens and green spaces and shrinking water bodies, both are happening due to human actions. It’s a proven fact that vegetation and water bodies can strongly contribute to local cooling. This means that when enough vegetation and water are included in the urban fabric, they can counterbalance the urban heat island effect, to the point of even cancelling out the urban heat island effect in some neighbourhoods. The urban heat island phenomenon is well known and understood. For instance, temperature measurements from thermometers located in cities are corrected for this effect when global warming trends are calculated.
Its difficult to assess how climate change will affect the urban heat island effect, and various studies show different results. However, two factors are worth mentioning here. First, future urbanization will expand the urban heat island areas, thereby amplifying future warming in many places all over the world. In some places, the nighttime warming from the urban heat island effect could even be on the same order of magnitude as the warming expected from human-induced climate change. In India, the problem may become glaring as the country has started seeing the pace of urbanisation picking up in recent years. Second, more intense, longer and more frequent heatwaves caused by climate change will more strongly impact cities and their inhabitants, because the extra warming from the urban heat island effect will exacerbate the impacts of climate change. Even some of the cities in Europe have started seeing the impact of heatwaves in recent years and thus global warming is not sparing anyone.
In short, cities are currently local hotspots because their structure, material and activities trap and release heat and reduce natural cooling processes. In the future, climate change will, on average, have a limited effect on the magnitude of the urban heat island itself, but ongoing urbanization together with more frequent, longer and warmer heatwaves will make cities more exposed to global warming. Therefore, our city planning should be viewed from new perspective, that is, it should also aim at tackling the problem of urban heat island. Henceforth, creating urban infra should not only include creating more houses, transport facilities and sewerage and sewage systems but also aim at avoiding creation of heat islands. Then only cities can become better liveable place.