Quick questions on Meteorological hazards: HSC Earth and Environmental Science Module 6

Tropical cyclones form over warm tropical oceans (above about 26.5 degrees Celsius) where warm, moist air rises, condenses and releases latent heat, driving a self-sustaining low-pressure system that spins because of the Coriolis effect. They bring destructive winds, torrential rain, flooding and a storm surge, a dome of seawater pushed ashore by wind and low pressure. Northern Australia is regularly affected; Cyclone Tracy devastated Darwin in 1974, and later cyclones such as Yasi (2011) caused major damage in north Queensland. Building codes in northern Australia were strengthened after Tracy.

Drought is a prolonged shortage of water caused by below-average rainfall, often intensified by high temperatures and evaporation. In Australia drought is closely tied to the El Nino phase of ENSO, when warmer ocean water shifts to the central Pacific and rainfall over eastern Australia falls. The Millennium Drought (roughly 1997 to 2009) caused severe water shortages, crop failures and ecosystem stress across the Murray-Darling Basin. Drought impacts build slowly and are managed through water restrictions, allocation rules and drought-resilient agriculture.

Floods occur when rainfall exceeds the capacity of rivers and the ground to absorb or carry water away. They are intensified during La Nina, by tropical cyclones, and by catchment factors such as saturated soils, steep terrain and cleared or paved land. The 2010 to 2011 Queensland floods and the 2022 floods in northern New South Wales and south-east Queensland inundated towns and caused major losses. Floods are managed through flood mapping, levees, dam operation and warning systems, and through land-use planning that limits building on floodplains.

Bushfires need fuel (dry vegetation), oxygen and an ignition source, and spread fastest under the combination known as high fire danger: high temperatures, low humidity, strong winds and abundant dry fuel after drought. They are a natural part of many Australian ecosystems but become disasters near settlements, as in the Black Saturday fires of 2009 and the 2019 to 2020 Black Summer. Management combines fuel-reduction (hazard-reduction) burning, fire-danger ratings, total fire bans, and the long-standing cultural burning practices of Aboriginal peoples, now increasingly used in formal land management.

Explain how warm ocean temperatures contribute to the formation and intensity of a tropical cyclone. [3 marks]

Using ENSO, explain why eastern Australia tends to experience drought and bushfire in some years and flooding in others. [4 marks]