Urban Sprawl and Spatial Population Estimation Using High-Resolution Satellite Imagery in the Mouila Watershed Areas (Ngounié, Gabon)

Gabon has experienced many difficulties since the 1990s in conducting its population census due to technical, financial, institutional, and political reasons, as well as numerous disputes over the data when these censuses are completed. Indeed, the country is often confronted with delays and repeated postponements between two censuses, officially linked to organizational constraints. In addition, the country faces alarming urbanization, particularly in the management and planning of its watersheds, which are subject to uncontrolled urbanization, thereby increasing the risk of flooding. Thus, this study aims to evaluate urban dynamics, estimate, and model the spatial distribution of the population in the watersheds of Mouila in the Ngounié province of Gabon. Faced with the challenges of expanding urbanization and traditional Gabonese censuses, we rely on a 2008 orthophoto and a 2023 high-resolution SAS Planet image to manually digitize the built-up areas in QGIS to obtain our map of urban sprawl. The population was estimated by assigning 5 persons per built unit, then spatialized using the geostatistical method of ordinary kriging. The results reveal an increase of 31.4% in built units and a spatial extension of population density in the Manvouaka, Doufoura, Doussama, and Dourougni basins. These extensions occurred from the city core towards the periphery. These very high densities follow the presence of basic infrastructure. This satellite-geostatistical approach offers an alternative for territorial planning and watershed management in a context of strong urban growth.