Downscaling Global Spatial Population Projections from 1/8-degree to 1-km Grid Cells

Global spatial population projections consistent with the Shared Socioeconomic Pathways (SSPs) are important for understanding interactions between societal and climatic changes, as well as mitigating adverse impacts of global environmental change. Current SSP spatial population projections were modeled at 1/8-degree grid cells. For studies requiring data with a finer spatial resolution, this technical note presents a simple approach downscaling the 1/8-degree spatial population projections to 1-km grid cells, using a 1-km ancillary map showing total population counts in 2000. The general spatial patterns shown by the resulting 1-km population projections are consistent with the original 1/8-degree projections. However, some spatial characteristics of both the 1/8-degree spatial population projections and the 1-km ancillary map propagated into the 1-km population projections as subtle spatial artifacts. The magnitudes of these artifacts vary across world regions, population types, and SSPs, and their potential effects on subsequent analyses should be evaluated case by case, considering what numerical and spatial precisions/details are necessary for those analyses. Although complex spatial population models may address the limitations of the downscaling products presented here, their development can be time-consuming. This projection can therefore be used as a defensible substitute until better options become available.