Urbanization is a phenomenon that refers to population transfer from rural to urban environments. It is associated with socio-economic parameters and the different way of life that these environments provide.
The United Nations (UN) suggest that the urban population was around 55% (4.2 billion out of 7.6 billion people) and by 2050 this ratio will increase to 68% (6.6 billion out of 9.7 billion people). Nevertheless, according to the new study, published in Nature Communications, the urbanization process does not develop evenly across large cities all over the world.
The characteristics of urbanization patterns were analyzed in terms of population growth and built-up area expansion. Scientists collected and analyzed satellite data (via the International Geosphere-Biosphere Programme) from 841 large cities that have a build-up area of more than 100km2. The cities were selected based on the countries' incomes to take into consideration the socio-economic factors that impact the urbanization process. In particular, 42%, 40.4%, 15.1% and 2.5% of the chosen cities belong to high-income, upper-middle-income, lower-middle-income and low-income countries, respectively.
The results of the research showed that most built-up area expansion occurs in the cities of upper-middle-income while the urban development in high-income countries was the lowest. Moreover, the cities that belong to the remaining income categories presented the highest population growth but did not show significant area expansion and infrastructure development. This fact was found to be deficient for those cities since it created severe crowding issues.
In addition, the study also focused on the development of green infrastructure. Approximately 39% of the cities studied presented more than 10% of green infrastructure (including Miami, Seoul, Chicago, the Pearl River Delta and more). According to data from 2018, 12% of the urban population lives in areas where green infrastructure thrives.
The authors make a specific mention regarding China's cities development over the past 20 years. In particular, it is suggested that the country is undergoing its largest urban expansion which accounts for 47,5% of the total expansion worldwide (data from 2001 to 2018). Currently, 19% of the total built-up area in large cities belong to China. “Due to the rapid economic growth in the study period, China invested a large amount of resources into infrastructure construction for advancing the urban living environment...” Ji Chen, co-author of the study and Professor at the Department of Civil Engineering, University of Hong Kong, stated.
The methods used for the current study provide a low-cost framework within which monitoring and evaluating the world's urban development is enabled. The findings suggest that urban expansion must be controlled especially in lower-middle-income and low-income countries where population growth is not accompanied by adequate infrastructure development.