Assessing the impact of climate variability on water balance and availability in Iwo, Osun state, Nigeria (1992–2022)

Effective water resource management is essential for achieving Sustainable Development Goal 6 (SDG 6), particularly in regions sensitive to climate variability. This study assesses the influence of climate change on water availability in Iwo, Osun State, Nigeria, over a 31-year period (1992–2022). The objectives are to (i) compute the annual water balance (WB) for the study period and (ii) examine long-term patterns in its key components within the Iwo community. Rainfall and temperature data were sourced from the Nigerian Meteorological Office, while evapotranspiration was estimated using the Papadopoulou-modified Thornthwaite model. The WB was calculated in Microsoft Excel, and temporal trends were evaluated using linear regression and the Mann–Kendall test. The findings show a declining trend in net water surplus (R2 = 0.0203, Y = –3.5282X – 498.6), suggesting a gradual reduction in overall water availability in the area. The findings show irregular rainfall patterns, prolonged dry spells, and hydrologic droughts now extending into April—two months longer than previously observed—posing challenges for sustainable domestic water supply. These variations underscore the need for adaptive and climate-resilient water management strategies. To mitigate these challenges, the study recommends integrated approaches including soil water conservation, rainwater harvesting, increased water storage capacity, and improved surface water utilisation. A key focus is the upgrading of the Aiba reservoir, Iwo’s primary but underutilised domestic water source, to enhance its efficiency amid declining rainfall reliability. Efforts to reduce evapotranspiration losses will help alleviate water scarcity and strengthen overall system resilience. For policymakers in Iwo Local Government Area and Osun State, the study emphasises the need to integrate climate data into local water governance, strengthen institutional capacity for monitoring water resources, and prioritise infrastructure investment and maintenance. Implementing these measures will improve water security, promote efficient resource use, and align regional water management policies with Nigeria’s national and global sustainability goals.