SUMMARY
Spatial trends of rainfall and reference evapotranspiration (ETo) are crucial for sustainable water resources management. Rainfall and ETo trends were evaluated and estimated using FAO Penman-Monteith model and their spatial distributions were mapped across Southeast Nigeria. Two spatial interpolation techniques, Inverse Distance Weighting (IDW) and Kriging in ArcGIS were employed for monthly, annual and seasonal rainfall and ETo. Results showed that rainfall increased gradually from North to South while ETo increased from South to North of the study area. ETo was found to be higher during dry seasons as the average rise in temperature within the period of study stood at 1.1%. There was a positive correlation of the predicted results obtained by the IDW and kriging methods with measured rainfall and ETo data, evaluated at R = 0.87(rainfall) and R = 0.83 (ETo) for IDW method, and R = 0.92 (rainfall) and R = 0.50 (ETo) for kriging method. This study provides background information on rainfall, ETo and climatic conditions for climate change studies, efficient crop water, and environmental management.