Flood Maps

Flood Maps is the Geohazards Risk Mapping Initiative's (GRMI) public collection of flood susceptibility and flood-extent maps for communities in Nigeria, with one event map for Ghana. GRMI, a volunteer-led Nigerian initiative founded in 2020, made them because flood-prone areas lacked up-to-date maps, which made it hard for authorities to plan mitigation and evacuation.

The interactive susceptibility web maps cover Ikorodu (Lagos), Ilorin East and Ilorin West (Kwara) and Maiduguri (Borno), and ArcGIS StoryMaps cover Kogi State and Jos North. For Kogi, GRMI combined SRTM 30 m elevation, topographic position, distance from permanent water from the Global Surface Water dataset, and a Landsat 8 vegetation index in Google Earth Engine. It classed the state from high to very low flood susceptibility and overlaid 3,593 surveyed schools, health facilities and markets. The study rated 548 of 1,476 health facilities and 686 schools as highly susceptible. The maps also estimate farmland at risk, and GRMI supplies an Excel list of the names, coordinates and susceptibility level of markets, schools, communities and farmlands; by 2022 it had mapped 25 communities.

Separate Google Earth Engine apps map flooded extent from Copernicus Sentinel-1 C-band radar by comparing images from before and after an event, for Kogi State (2022), Oshodi-Lagos (July 2024 storms) and Akosombo, Ghana (2023); the Oshodi app also reports flooded area, affected buildings and road length.

GRMI shares the maps with emergency institutions and ministries. In 2021 they went to Nigeria's National Emergency Management Agency (NEMA), and they are also published online for public use.