Stochastic Model for Soil Moisture Deficit in Irrigated Lands

Abstract

The growth of plants in an irrigated area is described as healthy or unhealthy, a two‐state process that depends on the moisture status of the soil. Probability distributions of the soil moisture deficit (SMD) and the critical soil moisture deficit (CSD) are derived by adopting a hydrological hazard function. Evapotranspiration, crop, and rainfall data from numerous locations within East Anglia, England, are used in a case study. Following water‐balance studies, crop and land‐weighted values of SMD are computed from the data, and the CSD is related to proportional yield reduction. The SMD and CSD are well represented by truncated Weibull distributions, as shown in the model development. Approximation by the exponential distribution is not statistically justifiable. Estimated parameters for different locations have low standard deviations and are not, in general, significantly different. Using regionally averaged parameters, the risks of yield reductions can be evaluated for planning purposes.