Response of waves and coastline evolution to climate variability off the Niger Delta coast during the past 110 years Olusegun A. Dada a,b,c , Guangxue Li a,b, ⁎, Lulu Qiao a,b , Yanyan Ma a,b , Dong Ding a,b , Jishang Xu a,b , Pin Li d , Jichao Yang e a College of Marine Geosciences, Ocean University of China, Qingdao 266100, China b Key Lab of Submarine and Processing Techniques, Ocean University of China, Qingdao 266100, China c Department of Marine Science and Technology, Federal University of Technology, Akure 340252, Nigeria d Department of Oceanography, Texas A&M University, College Station, TX 77843-3146, USA e National Deep Sea Centre, State Oceanic Administration, Qingdao 266061, China abstract article info Article history: Received 30 November 2015 Received in revised form 20 April 2016 Accepted 22 April 2016 Available online 26 April 2016 River deltas, low-lying landforms that host critical economic infrastructures and diverse ecosystems as well as high concentrations of human population, are highly vulnerable to the effects of global climate change. In order to understand the wave climate, their potential changes and implication on coastline evolution for environ- ment monitoring and sustainable management of the Niger Delta in the Gulf of Guinea, an investigation was carried out based on offshore wave statistics of an 110-year time series (1900–2010) dataset obtained from the ECMWF ERA-20C atmospheric reanalysis. Results of multivariate regression analyses indicate that interannu- al mean values of Hs and Tm trends tended to increase over time, especially in the western part of the delta coast, so that they are presently (1980 and 2010) up to 264 mm (300%) and 0.32 s (22%), respectively, higher than 80 years (1900–1930) ago. The maximum directions of the wave have become more westerly (southward) than southerly (westward) by up to 2° (33%) and the mean longshore sediment transport rate has increased by more than 8% over the last 80 years. The linear regression analysis for shoreline changes from 1987 to 2013 shows an erosional trend at the western part of the delta and accretional trends towards eastern part. The relationship between wave climate of the study area and atmospheric circulation using Pearson's correlation shows that the Atlantic Multidecadal Oscillation (AMO), North Atlantic Oscillation (NAO), East Atlantic pattern (EA) and El-Nino/Southern Oscillation (ENSO) Index explain significant proportion of the seasonal and annual wave variabilities compared to other indices. But it is most likely that the combination of these climatic indices acting together or separately constitutes a powerful and effective mechanism responsible for much of the vari- ability of the offshore Niger Delta wave climate. The study concludes that changing wave climate off the Niger Delta has strong implications on the delta coastline changes. However, other processes (such as fluvial discharge variability due climatic variability and anthropogenic effect) may be acting concomitantly with changes in wave regime and associated littoral transport to influence shoreline evolution along the Niger Delta coast. © 2016 Elsevier B.V. All rights reserved. Keywords: Wave climate evolution Longshore sediment transport Climate variability Coastline change Niger Delta 1. Introduction River delta systems are subject to a continuous evolution under different scales and their morphology is constantly changing in time and space and adapting to changing extrinsic conditions. They are high- ly vulnerable to the effects of natural climate variability, especially acceleration in sea-level rise, further rise in sea temperature, more extreme weather events and storms surges, altered precipitation and ocean acidification, as well as a human intervention (IPCC, 2007). A long-term shift in weather conditions is a normal part of the Earth's natural variability that is related to interactions between the atmo- sphere, ocean, and land, as well as changes in the amount of solar radi- ation reaching the Earth. According to the Intergovernmental Panel on Climate Change (IPCC) Working Group II, the risks of climate change to coastal population and ecosystems require the inclusion of a broader range of coastal drivers of changes; one of these key drivers, which has received inadequate attention, is wind-waves (IPCC, 2007). Waves have been identified as one of the important marine dynamic processes responsible for delta growth, and their effect in term of erosion and accretion on delta morphology is obvious when they are a dominant process (Nardin et al., 2013). More important, the significance of waves in shoreline evolution and other processes in the coastal areas, where numerous ecological and socio-economic activities such as agri- culture, fisheries and forestry, housing, mining, oil and gas extraction, Journal of Marine Systems 160 (2016) 64–80 ⁎ Corresponding author at: Key Lab of Seafloor Science and Exploration Technology, Ocean University of China, 238 Songling Road, Qingdao 266100, China. E-mail address: estuary@ouc.edu.cn (G. Li). http://dx.doi.org/10.1016/j.jmarsys.2016.04.005 0924-7963/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Marine Systems journal homepage: www.elsevier.com/locate/jmarsys