GIS-Based Flood Susceptibility Mapping Using Weighted Overlay and Analytical Hierarchy Process in Awka North, Anambra State, Nigeria

Flood susceptibility assessment provides an important spatial basis for land-use planning, drainage management and flood-risk reduction, particularly in areas experiencing increasing development and seasonal rainfall. This study developed a Geographic Information System (GIS)-based flood susceptibility map for Awka North Local Government Area, Anambra State, Nigeria, using elevation, slope, Topographic Wetness Index (TWI) and distance to drainage derived from a 30-m Shuttle Radar Topography Mission (SRTM) digital elevation model. The spatial datasets were harmonized in the Minna/Nigeria Mid Belt projected coordinate reference system (EPSG: 26392), standardized into Four susceptibility classes and integrated using a weighted linear combination. The adopted weights were 30% for elevation, 25% for slope, 25% for TWI and 20% for distance to drainage. An Analytical Hierarchy Process (AHP) sensitivity assessment was additionally conducted to examine the influence and consistency of an alternative weighting structure. The resulting flood susceptibility index ranged from 0.75 to 4.50, with a mean value of 2.7725. Of the 351.6831 km² of valid classified area, 226.7766 km² (64.48%) was classified as High susceptibility, 62.4915 km² (17.77%) as Very High, and 57.4371 km² (16.33%) as Moderate. The High and Very High classes together accounted for 289.2681 km² (82.25%) of the valid area. The AHP assessment produced weights of 33.81% for elevation, 20.48% for slope, 28.81% for TWI and 16.90% for distance to drainage, with a consistency ratio of 0.0225, indicating acceptable consistency. A 2022 historical flood inventory generated using Google Earth Engine identified 110 flood polygons covering approximately 1.3546 km². The resulting map represents a relative flood-susceptibility screening product rather than a direct prediction of flood depth, frequency or discharge. The study provides a spatial baseline for drainage assessment, development planning, flood preparedness and future validation using higher-resolution data, field observations and additional hydrological variables.