Bulk canopy resistance : determination and modeling for actual evapotranspiration estimation of maize

Due to the scarcity of water resources, the correct evaluation of water losses by the crops as evapotranspiration (ET) is very important in irrigation management. This work presents a model for estimating actual evapotranspiration on hourly and daily scales of maize crop grown in well water condition in the Lombardia Region. The present ET model is based on the Penman-Monteith equation using Katerji and Perrier approach based on the variable canopy resistance value rc that is a primary factor in the evapotranspiration process and it is not only a physiological parameter, but also has an aerodynamic component. Hence, it depends on multiple factors such as meteorological variables and plant water potential. This approach appears through a linear model in which rc depends on climate variables and aerodynamic resistance [rc/ra = f(r*/ra)] where ra is the aerodynamic resistance and r* is the critical resistance. The model has been applied with good results, and several authors have recommended it for practical purposes. The good accuracy reached shows that the model worked well and are clearly more accurate than those obtained by using the standard FAO 56 method.