Trends driving longer fire seasons, intense rainfall gathers pace

Changes to weather and climate extremes, which are driving more intense rainfall, longer fire seasons and rising sea levels, are happening at an increased pace across Australia, a report from the CSIRO and Bureau of Meteorology has found.

The State of the Climate 2022 report says the number of short duration heavy rainfall events is expected to rise in the future, while it projects increases in air temperatures, more heat extremes and fewer cold extremes in coming decades.

“We’re expecting to see longer fire seasons in the future for the south and east, and an increase in the number of dangerous fire weather days,” Bureau Climate Environmental Prediction Services Manager Karl Braganza said.

The report is the seventh in a series published every two years and draws on latest climate monitoring, science and projection information.

“The past decade has seen record-breaking extremes leading to natural disasters that are exacerbated by anthropogenic (human-caused) climate change,” the report says.

“Australia needs to plan for, and adapt to, the changing nature of climate risk now and in the decades ahead. The severity of impacts on Australians and our environment will depend on the speed at which global greenhouse gas emissions can be reduced.”

Australia’s climate has warmed on average by 1.47 degrees since 1910. There’s been an overall decline in rainfall between April and October across southern regions in recent decades, but in northern Australia rainfall has increased since the 1970s.

Observations show an increase in the intensity of heavy rainfall events that occur on timescales less than a day, with the intensity of hourly extreme events increasing by around 10% or more in some regions and in recent decades.

“Short-duration extreme rainfall events (such as for hourly rainfall totals) are often associated with flash flooding, which brings increased risk to communities,” the report says.

“This is particularly the case in urban environments, where the large amount of impervious ground cover (eg concrete) leads to increased flooding during heavy downpours.”

Changes in extreme rainfall won’t necessarily follow those in mean rainfall, with regions in southern Australia, which are expected to see continued long-term drying, still at risk from increases in extreme rainfall.

CSIRO Climate Centre Director Jaci Brown says concentrations of greenhouse gases, such as carbon dioxide, are at the highest levels seen on Earth in at least two million years.

The report documents the continuing acidification of the oceans around Australia, which have warmed by more than one degree since 1900, and says longer and more frequent marine heatwaves are expected into the future.

“We’re seeing mass coral bleaching events more often, and this year, for the first time, we’ve seen a mass coral bleaching on the Great Barrier Reef during a La Nina year,” Dr Brown said.

“The rate of sea level rise varies around Australia’s coastlines, but the north and south-east have experienced the most significant increases.”