The impact of climate variability on exportable surpluses of maize and soya beans in producing/exporting countries is well known. This situation necessitates the study of climate variability and yields in some of the major producer countries (Argentina, Brazil and the United States). This study aims to characterize the climate regimes of each region, seeking the highest degree of regional homogeneity and representativeness of yields and climate variables. The series variability is analysed according to various effects (different stages of crop development and conditioning of yield). The temperatures and rainfall occurring during the flowering stage exert greater conditioning on yield at the end of the crop cycle. Different theoretical fit models of yield are obtained for both crops with climate information from their core areas of high production.