Green Infrastructure as a Nature-Based Solution for Urban Flood Risk Reduction in Abuja, Nigeria

Abstract

Urbanisation has altered the hydrological functioning of Abuja, increasing the importance of approaches that can moderate stormwater generation alongside conventional drainage infrastructure. This study quantitatively evaluated the potential of green infrastructure as a nature-based solution for urban flood risk reduction in Abuja, Nigeria. The analytical domain of 247.8 km² was modelled under baseline, continued urbanisation, low, moderate and high green infrastructure scenarios corresponding to the built-up area reported for Abuja in 2020. Runoff volume and peak discharge calculations were carried out using simplified runoff method and rational method formulations for various degrees of green infrastructure cover (0%, 10%, 25% and 40%) for the appropriate intervention scenarios and varying rainfall depths (50 - 200 mm) by the weather generator. For a rainfall of 100 mm, the runoff for continued urbanisation was 16.850 million m³, which was 9.68% more than the runoff of 15.364 million m³ for the baseline. The reduction in the low, moderate and high green infrastructure scenarios was 3.23%, 16.13% and 29.03%, respectively. The results suggest that the more green infrastructure is present, the more runoff and peak discharge may be moderated, but the numerical results are estimates for the scenarios. The study calls for strategic incorporation of green infrastructure into the land use planning, drainage management and flood resilience framework of Abuja and preservation of conventional infrastructure and preparedness measures. It also suggests the use of calibrated spatial hydrological and hydraulic modelling to derive and set intervention levels which are defensible in an empirical manner.