Coral reefs, seagrass meadows and islands have a natural resilience to physical disturbances from weather events such as storms and cyclones.

However, climate change-induced shifts in weather patterns that affect the frequency, intensity or distribution of these disturbances will have important implications.

Trends

The Intergovernmental Panel on Climate Change (IPCC) found a warming climate is increasing the frequency and severity of many extreme weather events and is changing rainfall patterns.The IPCC predicts it is very likely that extreme rain events will become more intense and frequent in many regions.

According to the State of the Climate Report 2014, fewer tropical cyclones are projected for the Australian region, on average. However, it expects an increased proportion of intense cyclones.

Cyclones were responsible for 48 per cent of coral loss recorded by the Australian Institute of Marine Science’s Long-term Monitoring Program between 1985 and 2012.

Between 2004 and 2018, 10 cyclones of category three or greater crossed the Great Barrier Reef Marine Park. Impacts were most severe in the southern half of the region, causing significant damage to coral reef habitats.

Cyclone Hamish in March 2009 affected more than 50 per cent of the coral reefs in the region. Cyclone Yasi crossed the Queensland coast in February 2011 and was one of the most powerful cyclones to have affected Queensland since records commenced.

Cyclone Debbie in 2017 caused serious impacts to the central reef region.

Effects

Cyclones

Cyclones are low-pressure systems that derive their energy from warm tropical oceans — they form when sea-surface temperature is above 26.5°C.

Tropical cyclones can cause extensive damage to individual corals and to the structure of the Reef, and can affect large areas. The impacts can last for decades, if not centuries.

Powerful waves generated during cyclones can seriously damage habitats and landforms, particularly coral reefs and shorelines.

Cyclonic winds can also cause substantial changes in the shape of islands and coastlines, affect ocean currents and increase inshore ocean turbidity through suspension of sediments.

Intense rainfall

Intense rainfall and damaging storm surges can cause low-lying coastal areas to be inundated.

Large river foods that affect the central Great Barrier Reef have become more frequent since the late 19th century, and are now occurring on average every six years (1948–2011), compared with every 20 years between 1748 and 1847.

Floodwaters running off the land and into the Great Barrier Reef lagoon can form plumes laden with sediments (which can block light needed for seagrass and coral growth) and nutrients (which are linked to outbreaks of the coral predator, the crown-of-thorns starfish).

Extreme flood events are also resulting in more frequent freshwater impacts. The inflow of freshwater makes ocean waters less saline and can stress or kill many animals and plants that live on coral reefs.