“ET-CALCULATOR” A NEW MODEL TO ROBUSTLY CALCULATE EVAPOTRANSPIRATION IN EGYPT

Abstract

The Penman-Monteith (P-M) equation is widely recommended to calculate evapotranspiration (ET) because of its detailed theoretical base and its accommodation of small time periods. Thus, there is a need to develop a model to easily calculate ET and can be used by extension workers. The objective of this research is to use evaluate the MS Excel sheet capability to develop a program to calculate ET values in the Governorates of the Nile Delta and Valley. A model was developed called “ET-Calculator”. The model uses P-M equation to calculate ET. Weather parameters of 17 governorates in the Nile Delta and Valley were input (maximum and minimum temperature, mean of relative humidity, wind speed and solar radiation), as well as the elevation above sea level in order to calculate ET values. To test the validity of the model, the estimated ET values by ET-Calculator model were compared to the estimated ET values by BISm model. Closeness of both estimated ET values to each other was tested by Root Mean Square Error per observation (RMSE/obs) and Willmott index of agreement (d). The results indicated that ET-Calculator model estimated monthly and annual ET values in all governorates similar to the ET values estimated by BISm model, where RMSE/obs values were low and d values were high. These results implied that the presence of friendly and easy use program to calculate ET, such as ET-Calculator facilitate the calculation of water requirements for crops by extension workers and could improve the current situation of agricultural water management in Egypt.