A Simulation Model for Irrigation Scheduling Under Variable Rainfall

ABSTRACT Asimulation model was developed by coupling a simple daily rainfall generator to a water balance model that determines irrigation dates and amounts. The rainfall model uses average monthly data to generate daily precipitation and the water balance uses average ETQ values and estimates separately evaporation and transpiration as well as allowable depletion. The results of 50 years of simulating irrigation schedules for corn and sugarbeets at Cordoba and Badajoz, Spain and Davis, CA were analyzed to evaluate the effects of planting date, soil storage capacity and irrigation system constraints. Probability distribution functions of the date of first irrigation were developed for ideal and practical irrigation situations. A method is proposed based on the simulation to develop a predictive irrigation schedule at selected probability levels for optimal and suboptimal irrigation dates.