Drought Analysis and Soil Moisture Prediction

Soil moisture levels are predicted by a simple, conceptual accounting model run with daily rainfall and evaporation inputs. Model output is used to illustrate practical statistical procedures for drought frequency, duration and severity. Frequency is defined by the probability of a drought starting in a given month, duration is determined by run‐length analysis and severity is given in terms of soil moisture level. Predicted moisture contents for the top 100 mm (4 in.) of soil below ryegrass pasture are statistically similar to actual moisture levels measured in Canterbury, New Zealand. For this location, accurate rainfall forecasts could substantially reduce irrigation water demands.