Theme 5-2-Seasonal to interannual hydrologic prediction a case study from Sydney, Australia

Abstract

Effective use of available water resources is a serious problem facing the world as it enters the 21st century. An increasing demand and an ever-uncertain supply in the form of precipitation is a cause of concern to water resources managers. Another concern is the occurrence of severe and sustained droughts that deplete reservoir storage to dangerous levels, forcing operators to enforce water supply restrictions. Such droughts are often associated with long-term or low frequency climatic fluctuations, such as the El Niño Southern Oscillation (ENSO).

A recently completed research project at the University of New South Wales, Sydney, evaluated the feasibility of predicting the seasonal rainfall at Warragamba dam, a large water supply reservoir 70km west of Sydney. The study had three main aims: (a) to develop a criterion that was capable of quantifying the utility of a predictor when used for probabilistic forecasts of seasonal rainfall; (b) to formulate an effective approach for making probabilistic forecasts for selected lead times from the present; and, (c) to compare the effectiveness of using atmospheric indices (such as the Southern Oscillation Index) rather than a broader suit of hydro meteorological variables for predicting seasonal rainfall. Presented here is a summary of some of the methods that were developed and the results attained.