Temporal Variability in Annual Rainfall Anomaly in Selected Locations Over Lower Benue Basin, Nigeria: Implication for Flooding

This study examined rainfall variability across the Lower Benue Basin using the Rainfall Anomaly Index (RAI) to assess dry and wet years and their implications for flooding. Data on daily rainfall were collected from the following selected locations within the Basin. They are Ibi, Makurdi, Lafia, Jos, and Lokoja from 1971-2020 (50 years). The daily rainfall data were summed to obtain monthly and annual rainfall amounts. The data for the study locations were acquired from the Nigerian Meteorological Agency (NiMet). The extent of rainfall anomaly over the basin was determined using the Rainfall Anomaly Index (RAI). Results indicate that Lokoja experienced 26 dry and 24 wet years over 50 years, with the highest RAI of 5.2 in 2012, coinciding with a major flood. Makurdi recorded more positive RAI values from 1971 to 1991 and more dry anomalies from 2001 to 2020, indicating a general decrease in rainfall but no clear climate shift. Lafia shows a marked decline in rainfall, with positive RAI from 1971 to 1995 and drier conditions from 1996 to 2020, suggesting a climate change signal. Jos also exhibits a drying trend, with predominantly positive RAI from 1971 to 1992 and negative RAI thereafter, though the topography and river morphology still lead to flooding. Ibi shows 26 dry and 24 wet years, with drier conditions prevailing post-2011. Despite increasing dry conditions across the middle and upper basin, flood frequency remains high due to topographical and hydrological factors, especially in lower areas. The study therefore recommends that enhanced flood management measures are necessary to address ongoing flood risks despite declining rainfall, particularly in low-lying areas influenced by river morphology. In addition, tailored water conservation strategies should be implemented to support agricultural and environmental resilience in increasingly dry regions of the basin.