Quantifying urban expansion from 1985 to 2018 in large cities worldwide

Abstract The world has experienced widely distributed urbanization from local to global scales in the past decades. Urban expansion can bring multiple benefits for urban inhabitants, however it can also result in a series of environmental and ecological issues, such as carbon emission, air pollution, and biodiversity loss. Therefore, it is urgently required to conduct timely and quantitative monitoring of the dynamics of urban areas worldwide to support sustainable policy making for urban management and development, such as guiding rational urbanization in developing countries, uncovering inequality of global urbanization, and understanding the consistency of urbanization and population growth. However, we still lack high resolution information on the characteristics of global urban dynamics over the past decades. To fill this gap, we quantified spatiotemporal patterns of urban expansion from 1985 to 2018 in 501 large cities worldwide based on the 30 m fine resolution Global annual Artificial Impervious Area dataset. We then assessed the spatiotemporal patterns of urban expansion using the annual growth rate indicator. Our results showed that: (1) The total (mean) impervious surface area in these cities increased obviously from 50,778 (101.35) km2 in 1985 to 150,145 (299.69) km2 in 2018, i.e. the total (mean) impervious surface area tripled from 1985 to 2018. (2) cities in developed countries or high-income countries (e.g. North American and European cities) have a much higher impervious surface area than cities in developing countries or low-income countries (e.g. Asian and African cities). (3) cities in North America and Europe that are dominated by developed or high-income and upper-middle-income countries have lower annual growth rate of impervious surface than cities in Africa and Asia, which are dominated by low-income and lower-middle-income countries. In addition, cities in China and India experienced very high urban expansion rates during the past decades based on the annual growth rate indicator. The findings of this study could provide supporting information for land management and sustainable development for cities around the world.