GIS-Based Urban Flood Risk and Hazard Mapping: The Case of Mekelle City, Tigray, Ethiopia.

Abstract

Urban flooding is a growing threat in rapidly expanding cities of the Global South, yet many lack the high-resolution data needed for effective risk management. This study presents a spatially explicit flood risk assessment for Mekelle City, Ethiopia, by integrating remote sensing, Geographic Information Systems (GIS), and the Analytic Hierarchy Process (AHP). We standardized and weighed topographic, land use, drainage, soil, rainfall, and socio-economic vulnerability layers (consistency ratio, CR < 0.10) to generate a Flood Hazard Index (FHI) and a Vulnerability Index (VI), which were then combined to produce a Flood Risk Index (FRI). The model was validated using 127 historical flood locations, 58 field GPS points, and Sentinel-1 SAR-derived inundation polygons, achieving an overall accuracy of 85.6% (Kappa = 0.82; N = 208). Our results reveal that high and very high flood-risk zones cover 23% of the city and affect 27% of its population, concentrated in the low-lying central and northern sub-cities of Hadnet, Kedemay Weyane, and Ayder. This study provides a validated, transferable methodology for flood risk assessment in data-scarce urban environments, offering actionable insights for targeted drainage rehabilitation and nature-based interventions.