Mean Sea Level Analysis and Coastal Inundation Mapping of Lagos State, Nigeria Using Google Earth Engine

Abstract

Lagos State is a rapidly growing coastal region where population pressure, infrastructure development and low-lying terrain increase exposure to coastal inundation. This study integrated Sentinel-1 Synthetic Aperture Radar, Shuttle Radar Topography Mission Digital Elevation Model data and Google Earth Engine processing to assess mean sea-level trend and coastal inundation vulnerability between 2010 and 2023. The analysis used simulated sea surface height data, SAR-based water detection and an elevation-based vulnerability approach to identify low-lying and high-risk zones. The sea surface height analysis indicated a relative sea-level rise rate of 3.8166 mm/year, equivalent to an estimated cumulative increase of 53.43 mm, or approximately 5.34 cm, over the study period. Terrain analysis showed that land below 5 m above mean sea level occupied approximately 1534.1 km², while the high-vulnerability zone covered approximately 1527.9 km². Seasonal water extent derived from SAR data was 667.7 km² during January–March 2023 and 653.1 km² during June–August 2023. Monthly climatology showed that sea surface height generally increased from February to August, with the highest relative flood-risk period occurring between June and October. The findings indicate that low elevation is a major control on coastal inundation vulnerability in Lagos State and highlight the need for regular monitoring, improved elevation data and integration of vulnerability mapping into coastal planning.