DEVELOPMENT OFA MODEL FOR EVAPOTRANSPIRATION

Abstract

Several methods, empirical as well as physical processes based have been proposed in literature for estimation of meteorological parameters and for estimation of evapotranspiration. Choice of using a particular method in most cases is dictated by availability and accuracy of input data. Objective of this dissertation work is to develop models based on empirical correlations between climatic parameters (dependent variable) and other parameters (independent variable), which are generally known or can be easily measured. Thus, reference to various tables in FAO procedure (Doorenbos and Pruitt 1977) could be avoided and the procedure becomes simplified. First, a general model is proposed by compiling as well as developing regression equations. Table 3.4 shows that reference to eleven tables (as per FAO Procedure) has been avoided by using a general model. Only one table has to be referred, in the proposed general model. Keeping in view the limited range of climatic variation in Indonesia and particularly in Aceh Province, simple linear equations have been developed and a simplified model has been proposed. The model and input data are summarized in Table 5.8 (chapter 5). The simplified model has been applied to estimate ETo and Eo at Jambo Aye Project. Accuracy of the general model and the simplified model in estimation of extraterrestrial radiation (Ra), evaporation (Eo) and Potential evapotranspiration (ETo) in terms of percent of variation, coefficient of determination (R2), bias (B) and variance (V) have been compared. Extraterrestrial radiation (Ra) is estimated accurately in the general model as well as the simplified model. It is therefore not necessary to use complex mathematical expression given in the general model to estimate Ra. Development of a Model Evapotranspiration Simplified model consisting of linear regression equations can be used for estimation of potential evapotranspiration in the limited range of variation for meteorological parameters as happens in Indonesia. Accuracy parameters of the simplified model are found to be better than those of the general model. Simplified model has been developed specifically for limited range of variation in meteorological parameters in Indonesia. It is not applicable for other regions. General model is applicable for other regions also but accuracy has been compromised in consideration of general application.