Compound Coastal Flooding and Climate Change in the Niger Delta:Hydro-Climatic Modelling And Engineering Adaptation A Synthesis and Conceptual Modelling Framework

Abstract

The Niger Delta, Africa's largest deltaic and mangrove ecosystem, is increasingly exposed to compound coastal flooding the co-occurrence or successive interaction of fluvial discharge, pluvial runoff, storm surge, tidal elevation, and relative sea-level rise (RSLR) driven by anthropogenic climate change, land subsidence from hydrocarbon extraction, and rapid, unplanned coastal urbanisation. This paper synthesises the peer-reviewed and grey literature on compound flooding processes, hydro-climatic modelling frameworks, and engineering and nature-based adaptation options, and applies that synthesis to the Niger Delta as a regional case study. Evidence reviewed indicates that the Gulf of Guinea coastline is experiencing sea-level rise at approximately 3.9 mm/yr roughly 10% above the global average while localised land subsidence associated with hydrocarbon withdrawal (25–125 mm/yr at active well fields) compounds this signal into a relative sea-level rise of up to ~0.96 m by 2050 in the most affected settlements. Concurrently, regional rainfall intensity increased by an estimated 53% between 2012 and 2017 and a further 12% between 2017 and 2022, while upstream dam operations on the Niger and Benue river systems modulate the timing and magnitude of downstream discharge peaks. A conceptual hydro-climatic modelling framework coupling rainfall–runoff, river-routing, and storm-surge/tide hydrodynamic components is proposed for the region, drawing on established compound-inundation modelling practice (e.g., HEC-RAS, MIKE 21, ADCIRC-class coupling). Engineering adaptation options are evaluated along a grey–green–hybrid continuum, with particular attention to mangrove-fronted dike systems, elevated infrastructure, and adaptive, sensor-linked flood defences. The paper concludes that reducing compound flood risk in the Niger Delta requires integrated, basin-to-coast hydro-climatic modelling; regulation of subsidence-inducing extraction; mangrove restoration at scale; and hybrid engineering investment prioritised in the most exposed core states of Bayelsa, Rivers, and Delta.