Global Spatial Urban Expansion Scenarios Consistent with the Shared Socioeconomic Pathways (SSPs)

Urban land expansion is a prominent feature of contemporary urbanization. It is a nexus of interactions connecting many global changes in social, climate, and environmental systems. The SSP-RCP scenario framework is a powerful tool for investigating such interactions. SSPs contain qualitative narratives about future societal trends, as well as quantitative projections of population characteristics and GDP at various scales. However, urban land expansion has not been incorporated quantitatively nor qualitatively. Here we present a set of global spatial urban land projections consistent with the SSPs. We will discuss and compare plausible urbanization trends and patterns shown under different future scenarios. The projections were developed using a data science approach, exploiting best available datasets on urbanization and its driving forces, including a newly available global time series of fine-spatial-resolution remote sensing observations of urban land change over the past 40 years. Our modeling framework accounts for socioeconomic mechanisms at multiple spatial scales, and temporal evolutions of different stages of urbanization. The projections across scenarios show that the amount of urban land on Earth by 2100 strongly depends on societal trends in years to come, and may increase by a factor of 1.8-5.9 over the 21st century. The projected spatial patterns dynamically evolve over time, and similar amounts of urban land may exhibit different spatial configurations for the same geographic area under different scenarios.