Detection and spatio-temporal variation of marine heatwaves in the Gulf of Guinea, Nigeria

Abstract

Time series analyses spanning 30 years (1988-2017) on spatial and temporal variations in sea surface temperatures reveal the occurrence of marine heatwaves (MHWs) within the Nigerian segment of the Gulf of Guinea. For specific focus, three locations were also chosen along Nigeria's coastal zone, namely Lagos lagoon (western region), the Niger Delta (Forcados/Central region) and outer Cross River estuary (eastern region). Daily SST data was subjected to MHW detection algorithm, and then examined using Gaussian and Poisson distribution models to delineate the distribution of maximum intensities and frequency of occurrence of these extreme events, respectively. Determining the likelihood difference of maximum intensities of MHWs and the association between MHW count and occurrence year during the period was done using Kruskal-Wallis and Kendall rank correlation tests, respectively. Results show that the entire study area has been experiencing MHWs more frequently in recent decades, with the northwest region having higher counts. Strong seasonality exists, as more MHWs occurred in winter months (October to May). Peak month for MHW occurrence over the entire study area was May. November is shared as a peak month for the three focus coastal locations, although MHWs in Cross River and Niger Delta locations exhibited multi-modal patterns. None of the MHWs in Lagos location was categorized as severe. This study contributes to the World Climate Research Programme Grand Challenge on Weather and Climate Extremes.