Assessment of Climate Change Induced Trend, Magnitude, and Change Point Date in 24-Hourly Annual Maximum Series Rainfall Data for Port Harcourt Metropolis in Nigeria

The study determined the effect of changing climate on rainfall 24-hourly annual maximum series (AMS) downscaled data found to be statistically insignificant in trend for the Port Harcourt metropolis. The measured rainfall data for this study were collected for 35 years (1971-2005) from the Nigeria Meteorological Agency (NIMET). The 24-hourly (AMS) rainfall data extracted were further downscaled into shorter-duration rainfall using Indian Meteorological Department (IMD) and the Modified Chowdhury Indian Meteorological Department (MCIMD) method. The result of the slope obtained showed decreasing positive values of 0.5250 (at 0.25 hour) to 0.0249 mm/hr/year (at 24 hours) and 0.7625 (at 0.25 hour) to 0.0250 mm/hr/year (at 24 hours) for IMD and MCIMD models, respectively. The variable rate of change obtained showed 0.6 mm/year or 6.00 mm/decade at 24 hours. Relatively, the trend test for the 24-hourly monthly maximum series (MMS) also showed a p-value of 0.2289 which is greater than the alpha value at a 5% significant level with a slope value of 0.0006 to confirm the positive mild trend status of the 24-hourly AMS sample data. The trend change point date was obtained in 1988 by plotting the distribution-free cumulative (CUSUM) test, while the sequential MK (SQMK) test gave another year of change point date as 1994, further intensifying the positive trend change in the Port Harcourt metropolis. Therefore, proving the existence of mild and positive changing climatic conditions in the time series measured rainfall data for the study area.