Analysis of Extreme Precipitation Frequency Changes in Southeast Nigeria Under Observed and Projected Climate Conditions

Changes in extreme precipitation frequency and intensity have profound implications for flood risk management, infrastructure design, and urban planning in Southeast Nigeria's high-rainfall environment. This study analytically examines observed changes in extreme precipitation frequencies across Abia, Anambra, Ebonyi, Enugu, and Imo states and projects future changes under climate scenarios. Observed extreme precipitation trends were analyzed using daily rainfall records from 15 NiMet stations covering 1985 to 2022, applying ETCCDI extreme indices including RX1day, R95p, SDII, and CDD. Statistical extreme value analysis using the Generalized Extreme Value (GEV) distribution was applied to estimate return period rainfall totals and detect shifts in frequency-magnitude relationships across two sub-periods (1985-2002 and 2003-2022). Future projections were derived from statistically downscaled CMIP6 multi-model ensemble outputs for SSP2-4.5. Observed analysis reveals a statistically significant increase in SDII at 9 of 15 stations, indicating intensification of rainfall on wet days even as total rainfall days show no significant trend. GEV analysis confirms a positive shift in the 100-year return period daily rainfall amount averaging 11 percent across Southeast stations. Future projections indicate further intensification of extreme precipitation events by 2050-2070, with 100-year events becoming approximately 30-year events under SSP2-4.5. The study provides revised rainfall intensity-duration-frequency curves urgently needed for infrastructure design standards in the region. Keywords: extreme precipitation, Southeast Nigeria, GEV distribution, ETCCDI, IDF curves.