Analysis of Rainfall Trend and Variability in Lagos, Southwestern Nigeria

Abstract

The rainy season in the littoral city of Lagos has offered a lingering problem to water resourceWater resources managers and the region's socioeconomic activities over the years. In a changing climate, it is critical to understand how seasonal wet regimes vary in order to predict floodsFlood and manage water resourcesWater resources. The aim of this research is to assess rainfallRainfall changes using the trend and variability of two independent meteorological stations located inside Lagos’ coastal city. Monthly cumulative rainfallRainfall data was acquired and examined on monthly, seasonal, and annual scales for a 30-year period (1984–2013). Modified Mann–Kendall (MM-K) and Sen's slope estimator (Q) were used to estimate rainfall trendsRainfall trend and statistical significance tests, while the Precipitation Concentration Index (PCI) and Rainfall Variability Index (RVI) were used to quantify rainfall variability (RVI). Rainfall increased from January to May and November to December, but declined from July to August at both stations. In June, August, and October, however, both stations showed a distinct mix of upward and downward trends: dry season rainfallRainfall increased across stations, whereas wet season and yearly rainfall increased in the Ikeja station and fell in the Lagos Roof station, respectively. For Ikeja and Lagos Roof stations, PCI wet and dry seasons range from 9 to 20 and 9 to 42, respectively, while annual PCI ranges from 11 to 28 for both stations. In the wet and dry seasons, the Lagos Roof station had higher positive RVI tendencies than the Ikeja station depicting a high variability of rainfall within Lagos.