The paper presents a moisture availability index that is suggested for use in evaluating water balance conditions. It further presents a method for estimating irrigation requirements that has been evaluated using Brazilian climatic data. Comprehensive tables are provided including a detailed explanatory use of the tables on the following topics: (a) Mean monthly values of extraterrestrial radiation expressed as equivalent evaporation in millimeters per month at 20 degrees C; (b) Crop coefficients, K; and (c) Moisture availability analysis including climatic data.