| An existing solar radiation model developed at Ilorin which was found to be more reliable than Angstrom-type and Hargreaves solar radiation equations was used in the FAO Penman-Monteith reference evapotranspiration model (FAOPM) to obtain daily reference crop evapotranspiration (ET0) for a 32-year (1970 to 2001) period. The number of days having all the required input meteorological data was 9335. The sky conditions of the days were classified as clear, partially cloudy or cloudy depending on the cloudiness index, i.e. the ratio of diffuse solar radiation to total solar radiation. The ET0 values obtained with FAOPM were compared with predictions of three simpler empirical ET0 models, namely, the Hargreaves (HGRV), Jensen and Haise (JHSE) and... |
