Effective Rainfall Calculation Methods for Field Crops: An Overview, Analysis and New Formulation

Effective precipitation is important in irrigation scheduling decisions, is used to design new irrigation systems, and is a guiding factor for planning crop production practices. The methods for calculating effective rainfall for dry-land and wet-land crops were overviewed, analyzed and summarized in this paper. It is evident that the calculation methods have certain limitations, and also have merits and demerits. Performance of different methods was evaluated for effective rainfall of rice and deviations of results were found. As the methods are mostly empirical, such variation is expected other than the situation where they are developed/formulated. Process based formulation, particularly which considered crop ET, may suit under diverse situations. Under the current condition, Indian-1 and Japanese method estimated closer value, but may not yield better result under other conditions. The new formulation, which is based on the actual water expense, gave better/perfect estimation. New formulations pertinent to different practical/field situations are suggested, which will be useful for calculation of effective rainfall under different field and climatic conditions.