Understanding Climate Variability and Rainfall Distribution Patterns in Osogbo, Southwestern Nigeria

Abstract

Understanding rainfall variability and distribution is critical for climate adaptation, agricultural planning, and water resource management, particularly in tropical regions like Nigeria. This study analyses the temporal variability and distribution of rainfall in Osogbo, Southwestern Nigeria, over a 34-year period (1990–2023) using the Rainfall Variability Index (RVI) and the Precipitation Concentration Index (PCI). RVI was employed to quantify interannual rainfall anomalies and classify drought intensities, while PCI assessed the seasonal distribution of rainfall across annual, dry, and wet periods. Results from the RVI revealed a near-balanced pattern of rainfall anomalies, with 53% of the years showing below-average rainfall and 47% above average. Drought classification showed that 76% of the years experienced no drought, while 24% ranged from moderate to extreme drought conditions. Dry season analysis indicated higher variability, with a predominance of irregular and strongly irregular rainfall distribution (PCI > 16) in 85% of the years, suggesting unseasonal or erratic rainfall events. In contrast, the wet season exhibited more stable and uniform rainfall patterns, with 74% of the years showing PCI values below 10, indicating favourable conditions for rain-fed agriculture. The findings underscore increasing rainfall unpredictability, particularly during the dry season, and highlight the growing need for climate-resilient agricultural practices, improved seasonal forecasting, and integrated water management strategies. This study contributes to the understanding of local-scale climate behaviour and supports evidence-based decision-making in the face of climate variability and change.