Comparative Analysis of Climate Change Trend and Change-point for Daily Rainfall Annual Maximum Time Series Data in Four Gauging Stations in South-East Nigeria

The aim of the study was to conduct a comparative analysis of climate change trends and change-point detection in long-term daily rainfall annual maximum series (AMS) data across four gauging stations in South-Eastern Nigeria: Abakaliki, Enugu, Owerri and Umuahia. Utilizing 31-year rainfall records (1992–2022) from the Nigerian Meteorological Agency (NIMET), the research employed the Indian Meteorological Department (IMD) method to downscale daily rainfall to sub-daily durations. Trend analysis utilizing Mann-Kendall test and Sen’s slope estimator revealed statistically significant increasing rainfall trends in Abakaliki (Z = 2.75, p < 0.01) and Umuahia (Z = 2.75, p < 0.01), with Sen’s slope magnitudes ranging from 0.35–2.28 mm/year and 0.14–0.90 mm/year, respectively. Conversely, Enugu and Owerri exhibited non-significant decreasing trends. Change-point analysis using distribution-free CUSUM and sequential Mann-Kendall (SQMK) tests identified a significant shift in rainfall patterns in Umuahia (2002–2003), while other stations showed no statistically meaningful change points. The spatial variability in trends underscores the influence of geographical proximity to the Atlantic Ocean and localized urbanization. These findings emphasize the necessity of region-specific climate adaptation strategies, particularly for infrastructure design in regions with intensifying rainfall. The study advocates integrating non-stationary approaches in hydrological modeling especially at Abakaliki and Umuahia to address evolving climate risks in those regions.