Most studies evaluating future changes in climate extremes over Australia have examined events that occur once or more each year. However, it is extremes that occur less frequently than this that generally have the largest impacts on sectors such as infrastructure, health and finance. Here we use an ensemble of high resolution (∼10 km) climate projections from the NSW and ACT Regional Climate Modelling (NARCliM) project to provide insight into how such rare events may change over southeast Australia in the future. We examine changes in the frequency of extremes of heat, rainfall, bushfire weather, meteorological drought and thunderstorm energy by the late 21st century, focusing on events that currently occur once every 20 years (those with a 5% Annual Exceedance Probability). Overall the ensemble suggests increases in the frequency of all five extremes. Heat extremes exhibit the largest change in frequency and the greatest ensemble agreement, with current 1-in-20 year events projected to occur every year in central Australia and at least every 5 years across most of southeast Australia, by the late 21st century. The five capital cities included in our model domain are projected to experience multiple climate extremes more than twice as frequently in the late 21st century, with some cities projected to experience 1-in-20 year events more than six times as frequently. Although individual simulations show decreases in some extremes in some locations, there is no strong ensemble agreement for a decrease in any of the climate extremes over any part of southeast Australia. These results can support adaptation planning and should motivate further research into how extremely rare events will change over Australia in the future.

大多数评估澳大利亚未来极端气候变化的研究都检查了每年发生一次或多次的事件。但是，极端情况发生的频率通常比对基础设施，卫生和金融等部门的影响最大。在这里，我们使用了来自新南威尔士州和ACT区域气候模拟（NARCliM）项目的高分辨率（约10 km）气候合奏，以洞悉此类罕见事件在未来如何在澳大利亚东南部发生变化。我们研究了到21世纪末的高温，降雨，丛林大火天气，气象干旱和雷暴能量极端事件的频率变化，重点是当前每20年发生一次的事件（年发生概率为5％的事件）。总的来说，合奏表明所有五个极端的频率都增加了。极端温度表现出最大的频率变化和最大的合奏协议，预计到21世纪末，当前的20年1年事件将在澳大利亚中部每年发生，而在澳大利亚东南部的大部分地区至少每5年发生一次。我们的模型域中包括的五个首都城市预计在21世纪末经历极端气候的频率是两倍以上，而有些城市预计在20年中发生1次气候极端事件的频率将是六倍以上。尽管个别模拟显示某些地区的某些极端事件有所减少，但对于澳大利亚东南部任何地区的任何气候极端事件的减少都没有强烈的共识。