Global differences in urbanization dynamics from 1985 to 2015 and outlook considering IPCC climate scenarios

Abstract

Cities are expanding all over the world. In this study we aim to understand how the pace and scale of urban growth dynamics vary across geographies. This study contributes to the literature in four key ways: First, the study is comprehensive including all 1567 cities worldwide that had >300,000 inhabitants in 2015. Second, comparison of settlement dynamics of cities is performed in relation to continents, to geographic regions, to national levels and to city sizes. Third, a data-driven approach to delineate city boundaries allows for consistent comparisons across geographies. Fourth, the measured past urban trends are projected into the future and linked to climate scenarios used by the Panel on Climate Change (IPCC) to estimate where spatial focal areas of urbanization and climate-change meet. The study is based on remote sensing-derived geodata such as the World Settlement Footprint Evolution dataset for the period 1985 to 2015 and morphological urban areas. The key findings are: At continental scale, highest relative urban growth rates are measured in Asia. Among the IPCC regions, highest relative urban growth rates are in East Asia. In contrast, lowest growth rates are in Oceania and Europe. As expected, across most regions, there is a general decline in relative growth rates over the study period. One surprising finding is that absolute settlement expansion rates are not declining over time, but are rather relatively constant. It is also interesting to see that across and within countries growth rates of urban settlements vary widely in Asia, whereas in Europe there are only marginal differences. And finally, a look into the future reveals that certain regions can expect particularly high exposures. In South Asia and West Africa, for example, very high urban growth rates and a very high increase in predicted maximum rainfall are forecast. The greatest increase in extreme temperatures is predicted for Europe and North America. Settlement growth has already slowed there, so adaptation measures are taking center stage.