Contributions from different weather systems to rainfall in Tasmania, Australia

Tasmania, Australia’s largest producer of hydroelectric power, receives most of its rainfall from extratropical cyclones (ETCs) and cold fronts. Western Tasmania experiences up to 3 m of annual rainfall, primarily driven by midlatitude weather systems and their interaction with local topography, which supports hydroelectric power generation in the state. However, the weather systems influencing rainfall variability in the east – where most Tasmanians live and where rainfall is vital for agriculture – remain less studied. Using combined datasets of ETCs, cold fronts and thunderstorms spanning 1979–2015 over 5–50°S and 110–160°E, we examined the key weather systems driving Tasmania’s spatial and temporal rainfall variability. These weather systems collectively contribute over 80% of the state’s annual rainfall. A large proportion of total rainfall in eastern Tasmania is due to ETCs, whereas cold fronts play a greater role in the west. ETCs south of 40°S, particularly those passing through the Tasmanian region, are associated with heavy rainfall across the state. A statistically significant decline in rainfall (1979–2023) has been observed over western Tasmania, particularly during the warm season (November–April), raising concerns for hydroelectric resources. Our findings highlight the central role of midlatitude weather systems in sustaining Tasmania’s hydroclimate and underscore the need to better understand their future changes in a warming world.