Spatial and temporal variability of wet spells and their role in wet and dry summers and winters in Australia

Abstract Using three‐hourly ERA5 and ERA5‐Land reanalyses from 1979 to 2024, we determine the characteristics of wet spells in Australia in summer (October–March) and winter (April–September), focusing on northern and southeast Australia. Wet spells in summer account for up to 90% of seasonal precipitation in northern Australia, with a frequency of 20%–30% and a mean duration of 8–10 hours. In winter, wet spells of similar frequency contribute up to 96% of precipitation in southeast Australia, with a mean duration of 12–17 hours. Wet spells lasting six hours to one day account for the largest fraction (50%–60%) of seasonal precipitation in summer, whereas 12‐hour to two‐day wet spells contribute the most (50%–70%) in winter. Wet spells longer than 12 hours account for nearly 90% of the three‐hourly extreme precipitation events with a mean intensity of 3–4 mm·3‐h −1 . Shorter spells are associated with light showers with a mean intensity of 0.5–2 mm·3‐h −1 and contribute 10%–30% of extreme events. The increase in seasonal precipitation during wet years is primarily due to an increase in the frequency of wet spells in northern Australia. In contrast, increases in both wet‐spell frequency and intensity are important in southeast Australia. In both regions, wet spells longer than 12 hours contribute the most to the change in precipitation between wet and dry seasons. The synoptic environments for subdaily wet spells in northern Australia are tropical convection and monsoon low‐pressure systems. Longer wet spells show patterns similar to active monsoon bursts with a well‐developed monsoon trough. In southeast Australia, the synoptic patterns for subdaily spells resemble extratropical lows and fronts, while longer wet spells are mostly associated with cut‐off lows.