Study of Convective Storms and Flash Flood Risk in Ogun State

Intense convective storms are a primary driver of flash flood events in rapidly urbanizing areas of Southwest Nigeria, combining high rainfall intensities with saturated soils and overwhelmed urban drainage systems. This study examines the meteorological characteristics of convective storms and assesses flash flood risk in Ogun State, with emphasis on rapidly urbanizing LGAs including Obafemi-Owode, Ifo, and Sagamu. Ten-minute rainfall intensity data recorded at Abeokuta meteorological station from 2019 to 2023 were analyzed to characterize convective storm profiles, while flash flood occurrence records were compiled from the National Emergency Management Agency (NEMA) Ogun State office. Maximum daily rainfall frequency analysis was performed using the Gumbel extreme value distribution to estimate return periods for flood-generating thresholds. Results indicate that rainfall intensities exceeding 45 millimetres per hour, associated with organized mesoscale convective systems, occur on average 18 times per year in Ogun State. Flash floods typically manifest within 30 to 90 minutes of storm peak, leaving minimal response time for affected communities. The study identifies inadequate stormwater infrastructure designed for outdated intensity-duration-frequency norms as a critical vulnerability factor. Recommendations include revision of Ogun State's urban stormwater design standards and deployment of automated rain gauge networks to enable real-time flood early warning. Keywords: convective storms, flash flood, Ogun State, rainfall intensity, urban drainage.