Establishing the hierarchy of influence of drivers of seasonal rainfall variability in South Australia to inform seasonal rainfall forecasting

Seasonal rainfall forecasts are important for risk management in dryland and irrigated cropping, viticulture, emergency services, natural resource management and many other sectors. A key challenge in the development of skilful seasonal rainfall forecasts is the identification of the atmospheric and oceanic processes that drive the rainfall variability. Seasonal rainfall forecasts for South Australia (SA) currently have low predictive skill and we hypothesise that this is because the key drivers of SA’s rainfall variability have yet to be fully identified and therefore are not adequately represented in the forecast models. Previously, much of the focus in Australia has been on determining the causes of seasonal and annual rainfall variability in eastern and Western Australia, with little research conducted on SA’s rainfall variability. Therefore the aim of this study is to identify relationships between a host of potential climate drivers and seasonal rainfall across South Australia. First, a threshold method is used that accounts for the inherently non-linear nature of the links between large-scale climate phenomena and hydroclimatic variability. Then, a novel method for climate predictor selection is used to (a) identify the key combination of drivers that explains the most seasonal rainfall variability in different regions of SA and (b) determine the hierarchy of importance of the key drivers. This provides a set of metrics against which existing statistical and dynamical forecasting schemes can be tested and will also lead to the development of improved (or new) statistical forecasting schemes.