Investigating the relationship between East Coast Lows (ECLs) and East Australian rainfall

This study investigates the frequency and timing of six types of East Coast Lows (ECL) as well as their impact on rainfall along the Queensland and New South Wales coastline. By analysing the data from the Bureau of Meteorology's (BoM) NSW Maritime Lows database (1970-2006) as well as observed daily rainfall data from 27 BoM stations along the east coast, the relative importance of each type of ECL and their regions of preferential impact is quantified. This preliminary work was then repeated and expanded via utilisation of the BoMs recently updated ECL database: Maps and Tables of Climate Hazards of the Eastern Seaboard (MATCHES). MATCHES is a tool that identifies significant rainfall/wind/wave/water-level events on the Eastern Seaboard according to user specified thresholds while simultaneously displaying east coast low (ECL) tracks. This allows easy analysis of the relationship between the movement and location of an ECL and where its impacts are subsequently felt. Results suggest that the average timing of 5 of the 6 East Coast Low types (i.e. all except extropical cyclones) are converging around late autumn and early winter, whilst ex-tropical cyclones are occurring earlier, toward the middle of summer. Interannual rainfall totals are found to vary with that contributed by ECLs while the spatial distributions of daily rainfall attributed to the different types of systems were consistent with their associated area of formation. In conjunction with the cyclical nature of ECL frequency, the implications these results have on the distribution of rainfall, extreme events and water security along the densely populated east Australian seaboard are discussed