ABSTRACT
This chapter presents a statistical model for calculating the overall water balance for a crop growth period. It also defines the growing season in terms of the probability of obtaining a favorable period for non-irrigated crops between two given dates of year. The simplest method for characterizing moisture variability is a statistical analysis of rainfall. Since a frequency model of growing period must account both for intra- and interannual variabilities, time-step intervals that are chosen must satisfactorily reflect intra-annual change. Establishing statistical distributions of annual rainfall totals is not adequate. It is more useful to study the distributions of monthly totals; distributions of totals over 10-day, weekly, or 5-day intervals are even more useful. This geometric frequency model gives a statistical representation of the growing period that is both analytical and synthetic. It shows all the possible durations and positions of period, during which the facts of the cropping schedule, as well as the phenological phases of crop development, occur.
