HYDRO-CLIMATIC DYNAMICS OF NIGERIA'S RAINFOREST AGROECOLOGICAL ZONE

Abstract

The intensification of the global hydrological cycle is expected to alter rainfall characteristics and
atmospheric evaporative demand. This study analyzed a continuous 432-month (monthly) rainfall and
evaporation record covering 1990–2025 to assess hydroclimatic variability, stationarity and extreme-rainfall
frequency in Nigeria's rainforest agroecological zone. Descriptive statistics, Pearson correlation, Ordinary
Least Squares (OLS) regression, Pettitt's change-point test, Augmented Dickey–Fuller (ADF) testing, Johansen
cointegration analysis, the Aridity Index (AI), and extreme-event frequency analysis were applied. Rainfall and
evaporation showed a strong inverse correlation (r = −0.69, p < 0.001). The Pettitt test detected no
statistically significant abrupt change point (p = 0.75). The long-term mean Aridity Index was 22.42,
indicating a very high moisture surplus under the classification adopted in this study. OLS regression
indicated a marginal increase in annual rainfall of 1.62 mm yr−1 (p = 0.1178), while annual evaporation
showed no significant trend (0.18 mm yr−1, p = 0.46). Extreme rainfall months, defined as months exceeding
the 95th percentile threshold of 280.9 mm month−1, showed no clear increase in annual frequency over 1990–
2025. The results indicate substantial seasonal and interannual variability in rainfall but comparatively low
variability in evaporation. These findings provide a baseline for evaluating hydroclimatic variability and
water-resource management in a humid rainforest environment.