An integrated global model of local urban development and population change

High resolution models are essential to assess the localised impacts of global environmental change. To enable the estimation of the impacts of location-specific change, this paper presents a new modelling approach that disaggregates scenario-based national-level urban population estimates derived from the often-applied Shared Socioeconomic Pathways (SSPs) to high-resolution spatial grid (30 arc sec) representations of urban area and local population. By combining high-resolution spatial data, a sophisticated statistics-based calibration approach and a computationally efficient modelling framework, we can coherently describe local changes in urban area and population across the globe. Both developments are modelled simultaneously using the same scenario assumptions, but divergent patterns are shown to arise when, for example, population decline coincides with decreasing densities that yield an increase in urban area. The model can be applied in integrated global assessment studies focused on trends in local exposure to natural hazards or environmental impacts of urban change. The improved resolution of this new model is crucial to assess the impacts of future population growth in developing regions where most of the planet's biodiversity concentrates near large populations that live in clusters of smaller urban areas previously not captured by coarser resolution models.