Projected changes in east Australian midlatitude cyclones during the 21st century.

The east coast of Australia is regularly influenced by midlatitude cyclones known as East Coast Lows. These form in a range of synoptic situations and are both a cause of severe weather and an important contributor to water security. This paper presents the first projections of future cyclone activity in this region using a regional climate model ensemble, with the use of a range of cyclone identification methods increasing the robustness of results. While there is considerable uncertainty in projections of cyclone frequency during the warm months, there is a robust agreement on a decreased frequency of cyclones during the winter months, when they are most common in the current climate. However, there is a potential increase in the frequency of cyclones with heavy rainfall and those closest to the coast and accordingly those with potential for severe flooding.

Figure 2. a) Percentage change in the total number of ECLs per year between 1990–2009 and 2060–2079; b) Percentage change in the number of ECLs where the mean rainfall intensity within 500 km of the low center exceeds 6 mm/6 hours in at least one instance; c) Percentage change in the number of ECLs where the maximum rainfall intensity within 500 km of the low center exceeds 50 mm/6 hours in at least one instance; d) Percentage change in the number of ECLs where the mean hourly wind speed within 500 km of the low center exceeds 50 km/h in at least one instance. In all cases ECLs are selected using a model-dependent threshold that gives 22 ECLs per year in the current climate, with trends shown for the cool season (May– October) and warm season (November–April) separately.