Influence of climate drivers on variability and trends in seasonal rainfall in the Onkaparinga catchment in South Australia: a wavelet approach

Understanding the influence of climate drivers on the variability and trends of rainfall is useful for rainfall modelling. Previous research studies have identified various climate drivers associated with the variability of rainfall in Australia. Most of these studies have used traditional correlation techniques for this purpose, while in this study a relatively new technique termed the square wavelet coherence (WTC) has been used to identify the most influencing climate drivers for seasonal rainfall in the Onkaparinga catchment in South Australia. Moreover, the sequential Mann-Kendall test was used to assess the changes of trend over the period 1960 to 2010. The Southern Oscillation Index (SOI), Dipole Mode Index (DMI) and Niño3.4 were observed to be significantly associated with seasonal rainfall. The influence of climate drivers on rainfall variability varies with season, time and periodicity. For example, the wavelet coherence between SOI and winter rainfall indicates 2-to 3-year co-variability over the periods 1960 to 1985 and 1995 to 2010. For spring rainfall, 4- to 7-year fluctuations were significantly (at the 5% level) correlated with the DMI over the periods 1960 to 1980 and 2000 to 2010. This study shows that there is a strong non-stationary relationship between rainfall and climate drivers and these findings will be useful for understanding the non-stationary relationship between seasonal rainfall and climate drivers and hopefully will also help in stochastic rainfall generation and in the development of statistical downscaling models