Opinion – Claudio Bernardes: The urbanization of the world’s great cities in recent decades

The urbanization process has been intensifying globally in recent decades, and at the center of the development of this phenomenon are the population and urbanized area increases, especially in the world’s large cities.

Researchers from the Department of Civil Engineering at the University of Hong Kong and the Shenzhen Institute of Advanced Technologies published, in October 2020, a work that reports the study of this process in 841 large cities around the world, in developed and developing countries, with the aim of understanding how large global cities have developed in recent decades in terms of urban built-up area expansion, population growth and changes in green areas.

According to the economic classification of countries issued by the World Bank, the 841 large cities were divided into four groups: high income (over US$ 12,375 per capita), upper middle income (between US$ 3,996 and US$ 12,375 per capita) , lower middle income (between US$ 1,026 and US$ 3,995 per capita) and low income (less than US$ 1,025 per capita). Large cities are mainly located in high-income (353 large cities) and upper-middle-income (340 large cities) countries, while there are 127 large cities in lower-middle-income countries, and 21 in low-income countries.

The total urbanized area of ​​large cities increased between 2001 and 2018 from 270,000 square kilometers to 308,000 square kilometers, representing 36.1% and 38.5%, respectively, of the global urbanized area. The top 10 countries with the greatest evolution of built-up area, among the 841 large cities surveyed, are the United States (27% of the total built-up area), China (19%), Japan (6%), Brazil (4%), Germany (2.9%), India (2.8%), Canada (2.5%), Australia (2%), Mexico (1.9%) and Russia (1.8%).

Urban population growth is one of the driving forces behind the expansion of cities. Using the global population grid datasets in the years 2000, 2005, 2010 and 2015, the researchers found that 80% of large cities –676 out of 841 cities– recorded population growth. Among them, 22 major cities had a population growth of more than 2 million people.

These large cities are located mainly in Asia (15) and Africa (5), with one in South America (São Paulo) and another in Europe (Moscow). The average population growth rates of large cities in low-income and lower-middle-income countries from 2000 to 2015 are about the same; however, almost five times higher than the average rates of high-income countries.

The 20 most densely populated cities are in Asia and Africa, and the average population density of large cities in low-income countries is approximately three times higher than the average in high-income countries. Among these large cities, Dhaka, Kathmandu, Manila, Karachi, Istanbul and Cairo are the six most densely populated. They experienced rapid population growth between 2001 and 2018, while experiencing limited urban sprawl.

Finally, using the Modis sensor’s vegetation index as an indicator of green areas, vegetation areas with a significant increase trend and change in urban vegetation area since 2001 were identified. China, United States and Japan are the three main countries whose large cities contributed to the increase in green areas from 2001 to 2018, accounting, respectively, for 32%, 19% and 7.7% of the total in the 841 cities surveyed. Brazil, in this regard, is in the fifth position, with 3%.

Researchers estimate that the urbanized area of ​​the planet in the year 2100 could be, depending on the scenario, between two and six times larger than the existing area in the year 2000. This means that the need for investments in infrastructure can grow significantly, with economic repercussions extremely relevant to the municipalities and, thus, the models of functioning and occupation of cities, especially the larger ones, which must be immediately reviewed, reformulated and improved so that urban spatial development is economically and socially viable.