Spatio-Temporal Analysis of Rainfall Variability and Growing Season Dynamics in Nasarawa State, Nigeria

Rainfall variability has implications for agricultural planning and water resource management in Nasarawa State, Nigeria. This study examined rainfall trends, interannual variability, and growing-season dynamics over the 27-year period from 1997 to 2023. Monthly rainfall and rainy-day data obtained from the Nigerian Meteorological Agency were used to assess annual rainfall totals, rainy-day counts, rainfall onset and cessation, and length of growing season (LGS). Variability was examined across two subperiods, 1997–2010 and 2011–2023, while trends and statistical significance were assessed using linear regression and Student’s t-test. Mean annual rainfall increased by 95.4 mm in 2011–2023 relative to the mean of 1,189.6 mm recorded in 1997–2010. Mean annual rainy-day counts increased slightly from 177 to 179 days, whereas mean LGS declined from 187 to 186 days. Across the full study period, mean annual rainfall was 1,235.5 mm, with a coefficient of variation of 0.12. Rainfall anomalies shifted from −64 mm during 1997–2006 to +29.8 mm during 2007–2016 and +49.6 mm during 2017–2023. Rainy-day counts varied slightly across these intervals, while LGS remained comparatively stable. Regression analysis indicated upward trends in annual rainfall and rainy-day counts amid interannual fluctuations. Overall, the findings indicate a changing rainfall regime characterized by increasing rainfall totals without a corresponding extension of the growing season. The study provides evidence to inform agricultural and water resource planning and highlights the need for improved seasonal forecasting and stronger climate adaptation strategies to support resilience in the state’s predominantly agricultural economy.