What makes a city overpopulated

The World Migration Report WMR by the International Organisation for Migration argued that this mass movement of people is widely overlooked amid the global concern about urbanisation. And the report considers the widespread challenges, in terms of service provision, for the growing numbers of people moving into cities around the world. Where the significance of migration to cities is recognised, it is widely seen as a problem.

But this negative attitude towards migration to cities may well be mistaken. The WMR argues that problems of access to services — such as housing, sanitation, education or employment — that result from rural to urban migration, are not inevitable.

Rather, they are caused by poor planning. Although all socio-economic classes are reflected in migration to cities, migrants from rural areas are disproportionately poor, and inadequate planning is often a result of a weak political will to support them.

Yet, as the report pointed out, migrants are especially motivated individuals. It is not only the sheer numbers of people involved that makes migration worthy of attention. All around the world, populations of cities are now more diverse than surrounding rural areas. We convert these to a numeric scale for life satisfaction from one to four with one being Very dissatisfied and four being Very satisfied.

We measure urbanization in two ways: 1 based on residence in urban areas of differing population sizes and 2 based on population density in the county of residence. Our main results for the overall effects of urban population on happiness are shown in Figure 1, which gives regression-adjusted average differences in our life satisfaction measure relative to non-urban counties for urban size categories increasing in size from left to right.

Micropolitan areas are small urban areas not large enough to be considered metropolitan. We classify metropolitan areas as small, medium, large, and very large based on respective population groups of less than thousand, thousand to one million, one million to four million, and four million or larger. Our results show that all of the urban categories have lower average life satisfaction than the non-urban category used as the basis for comparison, but the differences for the micropolitan areas and small metro areas are small in magnitude and not a major source of concern.

However, the negative effect magnitudes increase with urban size and become sizable for the largest population groups. For example, very large metro areas reduce average resident life satisfaction in ways that move 2. This is a sizable magnitude in the life satisfaction literature and suggests that metropolitan size has considerable adverse effects on average happiness.

We also find consistently adverse effects of county population density on life satisfaction, even within metropolitan areas. We also explore effects of various natural amenities and report evidence that winter warmth significantly increases average happiness, consistent with expectations that people dislike cold winters. Understanding the overall effects of urbanization on life satisfaction is important in numerous ways, and our results strongly indicate that the overall effects are on average negative.

However, our study does not inform which factors are driving this negative effect. It is likely some combination of various adverse effects.

Global warming, intense flooding, deforestation, and decades of pumping out groundwater for residents are partly to blame. Jakarta could one day be uninhabitable. In February, monsoon rains paralysed the city of 14 million and displaced nearly 6, people, according to the Wall Street Journal.

An even worse deluge hit again in March, when four people were killed and 20, residences were evacuated. Photos of the disaster can be found here. Global warming means floods will happen more often. Research Scientist Owen Cooper, who works at the Earth Systems Research Lab in Boulder, Colorado says the sea level is rising faster in Indonesia than most parts of the globe at about six-to-nine millimetres a year.

Some areas, sea level is actually going down whereas others is going up. Jakarta… has a greater challenge in terms of sea level rise than most megacities, just because of its location where the sea level is rising fastest.

The project is expected to take 30 years to complete. In Shanghai, analysts believe steel, cement, and glass plants may have increased pollution, which has prompted the local government to consider giving local residents anti-pollution masks. Cooper, an air quality specialist, says China is experiencing more air pollution than anywhere in the world.

China's breakneck economic growth has led to serious air pollution in Shanghai Credit: Getty Images. We know from satellites that sulphur emissions from their power plants are starting to level off and come down. As city populations increase, it will become increasingly difficult for public transport to keep up with the strain. Traffic on the roads will also increase — whilst sustainable options such as electric scooters and bikes are helping alleviate road traffic in some places, by , there will be an extra 2 billion vehicles on the road worldwide.

IoT sensors and cameras can aid city planners in knowing which times of the day are busiest. This data can then be input into simulations or digital twins to predict the flow of traffic and test out adjustments in transport routes. The same method can be used to monitor where foot traffic is heaviest so that decisions can be made where to widen pavements and which areas to pedestrianise.