Establishing Climatic Change on Rainfall Trend, Variation and Change Point Pattern in Benin City, Nigeria

Abstract

This study examined the effect of changing climate for thirty-six years (1982-2017) on 24-hourly annual maximum time series (AMS) rainfall data for Benin City. The results show the existence of a trend, variation in magnitude, and change point dates. Trend analysis was performed using Mann-Kendall (MK) test and Sen’s slope estimator (SSE) applied to obtain the trend magnitude. A statistically significant trend was found for Benin City at a 5% level of significance. The MK |Z| statistic varied from 2.0710 to 2.1550 for IMD and 2.0844 to 2.0995 for MCIMD downscaling models, which were both greater than the critical Z-value of 1.96. The SSE gave the magnitude of the trend variation rate due to climate change at 24-hour duration as 1.008 mm/year (10.08 mm/decade) and 1.1376 mm/year (11.376 mm/decade) for the IMD and MCIMD models, respectively. Also, the trend change point analysis was conducted using the distribution-free cumulative sum test (CUSUM) and the sequential Mann-Kendall test (SQMK) which has rainfall pattern definite change point date for Benin City as 2005 from where continued a positive trend which intensified through the year 2015. Thus, proving the existence of increasing changing climatic condition for the study area.