Assessing the Potential of Compound Coastal Flooding from Oceanic Surge and Rainfall under Climate Change in the Niger Delta Region, Nigeria

Abstract

Compound coastal flooding, which results from the interaction between oceanic surge and intense rainfall, poses an increasing threat to low-lying coastal regions under a changing climate. However, in many vulnerable areas, including the Niger Delta in Nigeria, flood risk assessments still treat these drivers independently, which may lead to an underestimation of actual hazard exposure. This study investigates the spatiotemporal trends in sea surface elevation and precipitation along the coasts of six Niger Delta states, including Ondo, Delta, Bayelsa, Rivers, Akwa Ibom, and Cross River, to assess the potential for compound flooding. Sea surface elevation data were obtained from the HYbrid Coordinate Ocean Model (HYCOM) for the period 2000–2024, while precipitation data were derived from the Global Precipitation Measurement (GPM) IMERG dataset for 2001–2024. Monthly time series were generated for 10 km buffer zones around each referenced state, and linear trend analyses were conducted to examine changes over time. Results reveal a consistent decline in mean sea surface elevation anomalies across most states, with Akwa Ibom recording the lowest value (–0.0124 m) during 2020–2025. Precipitation trends also show negative slopes across all states, although none were statistically significant at the 0.05 level. Despite these declines, the persistence of coastal flooding in the region suggests that short-term sea-level fluctuations from tidal forcing and storm surges, high-intensity rainfall events, land subsidence from anthropogenic activities, and inadequate drainage infrastructure collectively contribute to flood risk. The findings indicate that reliance on long-term average trends alone is insufficient for understanding flood dynamics.