Estimation and comparison of reference evapotranspiration within Kaduna Central District, Nigeria, using four different methods

Abstract

The reference evapotranspiration (ETo) within Kaduna Central District, Nigeria was estimated from a 30-year climatological data using four different methods namely, Penman-Monteith (PM), Blaney Criddle (BC), Hargreaves (HGRV) and Piche evaporimeter (PiEv) (atmometer) methods. The study shows that the highest ETo values obtained from PM, BC and PiEv were 6.43 mm/day, 7.58 mm/day and 8.63 mm/day, respectively, and these occurred in February, except for HGRV which estimated its highest ETo (3.73 mm/day) in March. The lowest ETo values were obtained in August for all the methods. By means of the confidence index (c), agreement or concordance index (d) and correlation coefficients (r) statistics the BC, HGRV and PiEv ETo values were correlated with that of PM, as the standard. Results showed that BC, HGRV and PiEv gave c-values of 0.88, 0.48 and 0.67, respectively. Hence, BC-PM, HGRV-PM and PiEv-PM correlations were adjudged as excellent, bad and good, respectively, on the basis of criteria for interpretation of the performance of methods of ETo estimations. Blaney-Criddle reference evapotranspiration method gave the best estimate in comparison to the Penman-Monteith standard in the study area. Hence, the Blaney-Criddle ETo can be calibrated with the Penman-Monteith ETo and used effectively within the Kaduna Central District conditions for irrigation water management decisions. Keywords: Estimation and comparison, Reference evapotranspiration,  Methods, Kaduna Central District, Nigeria.