Analysing Rainfall Trends and Flood Risk in Coastal Nigeria: A Case Study of Calabar Using Mann-Kendall and Sen’s Slope Methods

This study investigates long-term patterns in rainfall and related flood frequencies in Calabar, southeastern Nigeria, using the Mann-Kendall trend test and Sen’s slope estimator. Covering twenty years (2003–2022), it utilises daily rainfall data from the Nigerian Meteorological Agency (NiMET) to examine changes in rainfall intensity and seasonality. The results reveal no statistically significant trend in annual rainfall (p = 1.0), although Sen’s slope indicates a slight downward trend (+7.907 mm/year). August was the only month with a statistically significant decrease in rainfall, with a Sen slope of – 0.387. The findings suggest increasing flood vulnerability despite the lack of statistical significance, emphasising the need for proactive flood management measures such as improved drainage, urban planning, and public awareness in the region.