The main aim of the crop model and water budget described here is to estimate the amount of water consumed which, in turn, is very closely related to crop yield. For each dekad, rainfall, crop water requirements and crop stage are known. At the same time, the water stress that could affect the crop during its development is also calculated in a cumulative way. This requires a preliminary investigation and collection of various agronomic parameters, i.e. cultivars, length of different growth stages, length of total growing period, crop coefficients allowing estimates of crop water requirements for each of the growth stages, soil water holding capacity, effective rainfall and soil runoff. This is an adjustment to climatic conditions of the average ETM values of cropped surfaces in an optimum development state and without any physiological constraints.
Water availability exceeds demand only during a limited period of the year.
In order to estimate real crop water requirements, PET values must be corrected. This correction brings us closer to the ETM values for the different crop development phases. The same information and analysis of rainfall and PET is used in assessing general crop feasibility under specific climatic conditions and to calculate the length of the crop growing period. The objective of the water balance model is to convert raw observations of the atmospheric environment into a set of parameters that are of direct importance to crop production. Basically, the water balance is the difference between the effective amounts of rainfall received by the crop and the amounts of water lost by the crop and soil due to evaporation, transpiration and deep infiltration.