Climatological Assessment of Rainfall Deviations for Sustainable Water Resources Management in the Anambra-Imo River Basin, Nigeria

This study analyzes annual rainfall variability in the Anambra-Imo River Basin, southeastern Nigeria, over a 30-year period (1990–2019), using baseline deviation and moving average techniques to assess hydrological patterns. A climatological baseline of 2407.76 mm was derived as the longterm Average Annual Rainfall (AAR), serving as a benchmark for evaluating inter-annual rainfall deviations. Annual totals were classified as either "Excess Rainfall" (positive deviation) or "Insufficient Rainfall" (negative deviation). To highlight long-term trends and reduce inter-annual fluctuations, a 5-year centered moving average was applied. Results reveal significant inter-annual variability, with years of both pronounced excess and significant deficit, indicating climatic volatility in the basin. The study provides critical insights for regional water resource management, agricultural planning, and climate adaptation strategies, emphasizing the importance of localized climate data in river basin management.