How does the El Nino Southern Oscillation and other large scale forcings impact daily - sub daily rainfall in eastern Australia?

Abstract

In recent years, there have been several well-documented studies showing the shifts in seasonal mean rainfall and temperature conditional on the ENSO phase. However, researchers have only recently started to investigate into the nature of rainfall variability at finer temporal scales. The study of rainfall variability at event scale is crucial as it can impact on the magnitude and frequency of both floods and droughts. For example, rainfall variability at small time scales may be conditional upon the underlying climate states, and may exhibit persistent structures consistent with larger scale patterns such as the likelihood of extreme droughts and floods. Non consideration of these climatic states may result in serious over or under estimations of catchment antecedent conditions, which has subsequent ramifications on floods. In addition, duration of dry periods within a season and amounts of rainfall that could fall during critical periods of a growing season cannot be satisfactorily deduced from larger scale rainfall predictions. As such, pertinent questions regarding the behavior of daily rainfall characteristics and wet day amounts during ENSO events as well as those stratified by large scale forcings (LSF) (i.e. the Inter-decadal Pacific Oscillation and Indian Ocean Dipole) are addressed. In this study, shifts in daily rainfall means and the number of wet days (per season) between opposing ENSO events are found to be significant across most stations in East Australia. Further tests on hourly rainfall also reveal differences in wet spell lengths at a sub-daily level. The stratification of other LSF to ENSO however does not appear to significantly exacerbate ENSO effects on rainfall at daily to sub-daily temporal scales.