Assessing GLOFAS Discharge Data for Urban Flood Modelling in Semi-Arid Region of Nigeria

Urban flood risk assessment in semi-arid regions of Nigeria is hindered by limited hydrological monitoring and rapidly changing land-use patterns. This study evaluates the capability of GLOFAS discharge data to bridge these data gaps by supporting hydrologic model parameterization and flood hazard analysis in an ungauged urban watershed, in Potiskum, Yobe State. In the main, the GLOFAS discharge data was validated for 8 years period in the nearby watershed – the Gongola river basin at Dadin Kowa. Using validated discharge as a proxy for observed flow, the HEC-HMS model was calibrated and validated under continuous and event-based conditions in a 37.5 km ² Potiskum watershed, yielding strong performance (NSE = 0.70–0.80; KGE = 0.83–0.86). Further, the validated models demonstrate the hydrologic plausibility of the global dataset for local-scale applications. Consequently, Intensity Duration Frequency (IDF)-based frequency storms were then used to generate design hydrographs using the calibrated hydrologic parameters, which were routed through a coupled 1D/2D HEC-RAS model to assess inundation dynamics. Results show rapid runoff generation typical of semi-arid urban catchments, with peak flows increasing systematically from 2.2 to a maximum of 3.8 m ³ /s for 2-year to 100-year events. Model outputs identified critical overtopping zones and drainage bottlenecks that drive recurrent flooding. Given severe space limitations in the dense urban setting, conventional storage-based LID strategies were infeasible, and targeted channel conveyance improvements emerged as the most practical adaptation pathway. Overall, the study demonstrates that GLOFAS-driven hydrologic modelling provides a viable and scalable approach for flood risk assessment and resilience planning in data-scarce urban basins across semi-arid Nigeria.