Contents lists available at ScienceDirect Journal of African Earth Sciences journal homepage: www.elsevier.com/locate/jafrearsci Recent coastal sea-level variations and flooding events in the Nigerian Transgressive Mud coast of Gulf of Guinea Olusegun A. Dada a,* , Rafael Almar b , Michael I. Oladapo a a Dept of Marine Science and Technology, Federal University of Technology, Akure, 340252, Nigeria b IRD-LEGOS (CNRS/IRD/CNES/Toulouse University), Toulouse, France ARTICLE INFO Keywords: Sea level variation Coastal flooding Nigerian transgressive mud coast Coastal erosion Gulf of Guinea ABSTRACT Significant warming and sea-level rise that will greatly impact the coastal zone is expected to intensify the coastal flooding occurrence on low-lying coasts in the next few decades. This challenge necessitates improving understanding of the possible trends and contributions of different oceanic forcing to the local coastal sea-level change at different time-scales at different locations. The present study seeks to understand different processes responsible for sea-level variations and coastal flooding events along the low-lying Nigerian Transgressive Mahin Mud coast in the Gulf of Guinea. The contributions of astronomical tides, altimetry-derived sea level, meteor- ologically forced non-tide residuals and wave run-up to coastal sea-level variations were assessed over the period between 1993 and 2016. The results show a distinct seasonal cycle, with more occurrences during summer/wet season and fewer events in winter/dry season, typically connected to the annual cycles of swell-waves. The leading contributor to total sea-level variations along this mud coast, at daily, seasonal and inter-annual time- scales was wave run-up. However, the leading contributor to total sea-level variations at the monthly (sub- annual) time scale was astronomical tides. Results further show that while the altimetry-derived sea level was responsible for the trend in total sea-level variability, the wave run-up was the major forcing responsible for the extreme coastal flooding events. However, the interaction between wave run-up and astronomical tides further contributed to the extreme/coastal flooding events along the mud coast. It is concluded that the increase in the coastal flooding events in the last 12 years of the study may have rendered the study area vulnerable to chronic erosion and flood hazards, which may have triggered the accelerated rate of coastal degradation in the study area. 1. Introduction The Intergovernmental Panel on Climate Change (IPCC) has pre- dicted a significant warming and a global sea-level rise for this century (IPCC, 2014), which is expected to intensify the coastal flooding oc- currence on low-lying coasts (Wong et al., 2014). The coastal flooding may occur concurrently with the major storms, thereby causing over- wash and erosion phenomena, especially if they occur at the same time as the extremely astronomical high tide (Anderson et al., 2018; Pirazzoli et al., 2006). This predicted sea-level rise in response to global climate change is expected to directly and significantly impact the coastal zone, displace ecosystems, alter geomorphological configura- tions and their related sediment dynamics, and increase the vulner- ability of social infrastructure (Bornman et al., 2016; Ranasinghe et al., 2012; Nicholls and Cazenave, 2010). More importantly, these impacts will be felt through changes in mean sea level and the frequency or intensity of extreme sea-level events. The African coast, a low-lying coastal area, has been declared as one of the most vulnerable areas to experience annual or more frequent flooding, implying an increase in flood frequency that will require increased protection, migration, etc. (Giardino et al., 2018; Ndour et al., 2018; Nicholls et al., 1999). It is, therefore, necessary to improve our understanding of the possible trends of change and contributions of different oceanic forcing to the local coastal sea-level change at different time-scales. As stated by Pirazzoli et al. (2006), the local effects of storms are expected to differ from one location to the other, depending on the exposure and possible changes in the leading trajectories of atmospheric disturbances at that location. Sea level variations in the coastal ocean are caused by the combination of different processes superimposed at global, regional and local scales (Melet et al., 2016, 2018; Almeida et al., 2018; Vitousek et al., 2017; Rueda et al., 2017). The most important contributors to mean sea level rise, whether at global, regional or local scales, are https://doi.org/10.1016/j.jafrearsci.2019.103668 Received 26 April 2019; Received in revised form 7 October 2019; Accepted 9 October 2019 * Corresponding author. E-mail address: oadada@futa.edu.ng (O.A. Dada). Journal of African Earth Sciences 161 (2020) 103668 Available online 14 October 2019 1464-343X/ © 2019 Elsevier Ltd. All rights reserved. T