SEVERE weather events can be devastating. But when events hit simultaneously, or consecutively, in both time and space the consequences can be catastrophic to lives, infrastructure, economies and ecosystems.
Dr Kathleen McInnes, leader of the Climate Extremes and Projections group at CSIRO, is a key contributor to the IPCC Special Report on the Oceans and Cryosphere in a Changing Climate (SROCC).
Her contribution examines the impact of climate change on an emerging area of research into ‘compound events’.
Risks amplify when phenomena—such as heavy rainfall and sea-level rise, or bushfire and drought—collide.
But understanding the interactions between any number of competing events is much more complex than understanding the individual drivers.
Compound risks and events
The IPCC special report assesses the impacts of climate change on ocean, coastal, polar and mountain ecosystems, as well as the human communities that depend on them.
McInnes contributed to Chapter 6, which examines extreme events, tipping points and compound risk.
“Compound risks arise from the interaction of hazards,” she said. “They can be multiple coincident or sequential events that interact with exposed systems or sectors.”
The case studies in McInnes’ chapter emphasise how compound events stress the capacity of both society and the environment to respond to its impacts. She highlights the 2015/2016 summer in Tasmania, which started with a severe El Niño.
“October 2015 to April 2016 was the driest warm season on record,” McInnes said.
“At the time, together with drought conditions, this preconditioned the island’s highland environment for summer bushfires.”
Lightning strikes ignited fires across the state, burning more than 120,000 hectares, at a cost of more than AUD $50 million to the local economy.
In January of the same season, an intense low-pressure system inundated northeast Tasmania with heavy rainfall and floods.
As emergency services juggled both bushfires and floods, they called on support from other states. But the run of ‘bad luck’ didn’t end there. An intense marine heatwave off the east coast also persisted for 251 days through this period.
The combination of drought, fires, floods and the marine heatwave affected the agriculture, forestry, fishing and energy sectors. The Tasmanian Gross State Product (GSP) dropped to 1.3 percent —well below the anticipated growth of 2.4 percent.
“The marine heatwave caused an outbreak of disease in farmed oysters and the deaths of wild shellfish,” McInnes said.
“The energy sector also experienced a severe cascade of impacts due to the climate conditions and system inter-dependencies.”
What is the future of compound events?
As the atmosphere continues to warm, weather extremes will only intensify. Compound events will become more frequent.
“Current climate projections highlight the increasing risk of these multiple impacts,” said Dr Sarah Boulter, a Research Fellow with the National Climate Change Adaptation Research Facility.
The facility supports Australia’s decision-makers manage the risks of climate change and sea-level rise.
“Compound events are not front of mind for most people thinking about their own risks, or even the risk that climate change presents,” Boulter said.
“But, as our summers experience more frequent and intense heat waves, increased bushfire risk, more intense storm events and rising sea levels, we can expect multiple impacts—more frequently and for longer in the year.”
“It begins to sound quite unrelenting.”
A focus on the coast
Since the impact of compound events can span across years, Boulter says state and local governments are now assessing compound risks in their planning processes.
She works on CoastAdapt—a tool that supports anyone managing climate change risks in coastal areas. McInnes’ group at CSIRO contributed the climate projection modelling for the data visualisation tools.
“The impact of climate change on Australia’s coasts is amplified by a number of factors,” Boulter said.
“Because 85 percent of Australia’s population lives along the coast this is where much of our critical infrastructure is: where our homes and livelihoods are, where the economy is driven from, and where we love to holiday.”
But the coast is also exposed to both marine and terrestrial impacts. Storm surge combined with higher sea levels causes damage to beaches, foreshores and properties. On land there is risk of overland and river flooding at the same time during storms.
And extreme heat and bushfires pose a risk in the calm periods.
As these events become more common, the time to recover lessens,” Boulter said.
CoastAdapt provides accessible science and guidance on dealing with the financial, social, and legislative barriers in preparing for future climate risks to individuals and organisations.
“The aim is to move towards implementing action, making regular reviews and adjustments over time,” Boulter said.
“So, if your house is at risk of flooding, is there a way to protect the building, or do you need to consider moving?”
“CoastAdapt helps you consider your options to reduce each risk.”
Where to now?
“Compound events are not a case of just ‘bad luck’,” McInnes said.
“Understanding how future compound events occur—as well as estimating their severity—is a challenge for scientists, but an important one for climate adaptation.”
She says climate scientists and decision-makers need to work closely together to understand how to mitigate the risk of compound events.
Boulter says some local councils are now considering options such as sea walls and groynes (sand containers that act as shore protection structures), ecosystem restoration, and changes to planning regulations to protect coastal communities from climate change impacts.
“Most are also engaging with their communities to understand what they want for the future,” Boulter said.
“Though taking action to reduce the impacts of climate change is what we should aim for, we do have excellent tools, such as CoastAdapt, that can help decision-makers prepare,” McInnes said.