The influences on Australian east coast lows in present and future climates

Abstract

East Coast Lows (ECLs) are midlatitude cyclones that develop on the east coast of Australia, responsible for the majority of coastal flooding, large waves, erosion, and dam-filling events. Because of their impacts, there is a need to better understand both how and why they develop, and how they may change in coming decades. The objective of this thesis was to use a combination of observational datasets and regional climate model simulations to improve our understanding of the influences on the frequency, characteristics, and impacts of East Coast Lows in both the present and future climates. Key outcomes include: - Assessing the representation of ECLs in reanalysis data, and identifying that the observed interannual variability and seasonal distribution of East Coast Lows are sensitive to the identification method used. - Evaluating the skill of high-resolution regional climate models to reproduce the observed frequency and distribution of ECLs - Developing the most robust projections of future ECL activity in the coming century, using an ensemble of regionally-downscaled climate model projections for Australia and a number of automated methods for identifying ECLs. This identified a robust decline in future ECLs during the winter months, but large uncertainty in the warm season and for ECLs close to the coast. The frequency of ECLs associated with heavy rain is likely to increase in both seasons. - Quantifying the impact of the East Australian Current and Great Dividing Range on the frequency, intensity, and impacts of ECLs using a suite of multi-year regional climate model experiments. Warmer oceans were identified as important for the development of weak to moderate ECLs, with a 20% increase in ECL frequency for a 1 2°C increase in coastal sea surface temperatures, with a lesser influence on the most intense events. Changes to topography had a smaller impact on the frequency and distribution of ECLs, with a 7 10% decline in ECLs when topography was removed. However, the detailed effects of topography on ECL characteristics were sensitive to the modelling approach used. In total, this thesis represents a substantial improvement of our understanding of East Coast Lows in regional climate model simulations.