Parched Australian Woodland vs. Resilient Forest

Australia's Angry Summer: What Happens When Heatwaves Hit Hard?

Samir D’Costa in Climate & Environment August 2025 • 5 min read.

"Unpacking the impact of extreme heat on Australia's woodlands and forests, and what it means for our planet's future."

Climate change is no longer a distant threat; it's our present reality. Temperatures are climbing, and extreme weather events are becoming more frequent and intense. To predict and prepare for the future, we need to understand how our ecosystems are responding to these changes, particularly to temperature spikes and prolonged droughts.

While researchers have extensively studied heat waves' effects on Europe and the US, Australia's unique environment demands its own investigations. In the summer of 2012/2013, Australia experienced an unprecedented heat wave – so extreme it was nicknamed the 'Angry Summer.' This event provided a critical opportunity to study the impact of extreme heat on the continent's vital carbon and water cycles.

This article delves into findings that combine on-the-ground measurements with sophisticated modeling to reveal precisely how the 'Angry Summer' impacted southern Australia's woodlands and forests. We'll uncover which ecosystems proved surprisingly resilient, which faltered, and what these responses tell us about the future of Australia's landscapes in a warming world.

How Did the 'Angry Summer' Impact Carbon and Water?

Parched Australian Woodland vs. Resilient Forest

During the 'Angry Summer,' researchers synthesized data from seven woodland sites and one forest site across southern Australia. These sites, equipped with eddy-covariance instruments, continuously measure the exchange of carbon dioxide, water vapor, and energy between the land and the atmosphere. By comparing measurements during the heat wave to normal conditions, scientists could determine the precise effects of the extreme heat.

The study revealed a tale of two ecosystems: water-limited woodlands and energy-limited forests. Each responded differently to the extreme heat, highlighting the complex ways that climate change can impact diverse environments.

Woodlands Under Stress: The woodlands experienced a significant decrease in latent heat flux (23%), indicating reduced evaporative cooling. They also saw a dramatic increase in the Bowen ratio (154%), showing that more energy was being released as sensible heat, further warming the atmosphere. Most alarmingly, carbon uptake plummeted by 60%, severely diminishing the woodlands' ability to act as carbon sinks.
Forests Show Resilience: In stark contrast, the forest ecosystem actually increased its latent heat flux (151%), helping to cool the environment. The Bowen ratio decreased (19%), and carbon uptake surged by 112%. This suggests that the forest was able to capitalize on the heat, perhaps due to greater access to water reserves.
Respiration Surges: While the forest fared better overall, all sites experienced a surge in ecosystem respiration (up to 139%). This means that plants were releasing more carbon dioxide into the atmosphere due to the heat, partially offsetting any gains in carbon uptake.

Although daytime photosynthesis continued, its effectiveness was considerably reduced. The number of hours each day that ecosystems acted as a carbon sink also decreased, resulting in woodlands switching to carbon sources. Furthermore, precipitation after the initial and most intense part of the heat wave assisted in restoring carbon sink function, lowering the Bowen ratio, and boosting evaporative cooling in temperate woodlands. Gross primary production in woodlands recovered quickly with precipitation and cooler temperatures, but respiration remained elevated.

What Does This Mean for Australia's Future?

This research provides critical, early evidence that the carbon sinks of significant areas of Australia may not be sustainable in a future characterized by more frequent, intense, and prolonged heat waves. While forests demonstrated a degree of resilience, the stressed response of the woodlands raises concerns about long-term carbon storage and the potential for positive carbon-climate feedbacks. Further monitoring and research are essential to understand the long-term consequences of extreme heat events on Australia's ecosystems and to inform effective climate adaptation strategies.

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This article is based on research published under:

DOI-LINK: 10.5194/bg-13-5947-2016, Alternate LINK

Title: Carbon Uptake And Water Use In Woodlands And Forests In Southern Australia During An Extreme Heat Wave Event In The “Angry Summer” Of 2012/2013

Subject: Earth-Surface Processes

Journal: Biogeosciences

Publisher: Copernicus GmbH

Authors: Eva Van Gorsel, Sebastian Wolf, James Cleverly, Peter Isaac, Vanessa Haverd, Cäcilia Ewenz, Stefan Arndt, Jason Beringer, Víctor Resco De Dios, Bradley J. Evans, Anne Griebel, Lindsay B. Hutley, Trevor Keenan, Natascha Kljun, Craig Macfarlane, Wayne S. Meyer, Ian Mchugh, Elise Pendall, Suzanne M. Prober, Richard Silberstein

Published: 2016-11-01

Everything You Need To Know

How did the 'Angry Summer' of 2012/2013 specifically impact carbon and water cycles in Australian woodlands and forests?

During the 'Angry Summer' event, water-limited woodlands experienced a notable decrease in latent heat flux by 23%, which signifies a reduction in evaporative cooling. There was also a dramatic surge in the Bowen ratio by 154%, pointing to increased release of energy as sensible heat. Most critically, carbon uptake in these woodlands plummeted by 60%, severely compromising their ability to act as carbon sinks. In contrast, energy-limited forests increased latent heat flux by 151%, helping to cool the environment. Their Bowen ratio decreased by 19%, and carbon uptake surged by 112%. However, both woodlands and forests experienced a surge in ecosystem respiration.

What do the different responses of woodlands and forests during the 'Angry Summer' imply for Australia's future carbon storage and climate?

The research indicates that significant areas of Australia's carbon sinks might not be sustainable given the increasing frequency, intensity, and duration of heat waves. The stressed response of the woodlands raises concerns about long-term carbon storage and the potential for positive carbon-climate feedbacks. While forests showed resilience by increasing latent heat flux, decreasing the Bowen ratio, and surging carbon uptake by 112%, all sites experienced a surge in ecosystem respiration, partially offsetting gains in carbon uptake. Further research and monitoring are needed to fully understand the long-term consequences of these extreme heat events and to develop effective climate adaptation strategies.

Can you explain latent heat flux, Bowen ratio, and carbon uptake in the context of how the 'Angry Summer' affected Australian ecosystems?

Latent heat flux refers to the heat energy required for water to change phases, such as evaporation. A decrease in latent heat flux, as seen in the woodlands during the 'Angry Summer,' means less water is evaporating, reducing the cooling effect. The Bowen ratio is the ratio of sensible heat flux to latent heat flux. A higher Bowen ratio, as observed in the woodlands, suggests that more energy is being released as sensible heat, contributing to further warming of the atmosphere. Carbon uptake refers to the process by which plants absorb carbon dioxide from the atmosphere through photosynthesis. A decrease in carbon uptake indicates a reduced ability of ecosystems to act as carbon sinks, exacerbating climate change.

What is ecosystem respiration, and why is the surge in respiration observed during the 'Angry Summer' a cause for concern?

Ecosystem respiration is the process by which plants release carbon dioxide back into the atmosphere. During the 'Angry Summer,' both woodlands and forests experienced a surge in ecosystem respiration (up to 139%), partially offsetting gains in carbon uptake. This means that even though some ecosystems may initially show resilience by increasing carbon uptake, the increased respiration rates can diminish their overall effectiveness as carbon sinks. This is particularly concerning because it highlights a potential feedback loop where increased temperatures lead to increased respiration, further accelerating climate change. Gross primary production refers to the total rate at which an ecosystem captures and stores carbon. In this case, gross primary production recovered with precipitation and cooler temperatures, but respiration remained elevated, which tells us that the ecosystems are more vulnerable to ongoing changes.

What was Australia's 'Angry Summer,' and why is it considered a significant event for studying the effects of climate change on ecosystems?

The 'Angry Summer' was an unprecedented heat wave in Australia during the summer of 2012/2013. It was so extreme that it provided a unique opportunity to study the impact of extreme heat on the continent's carbon and water cycles. It is significant because it highlighted the different responses of water-limited woodlands and energy-limited forests to extreme heat. The woodlands experienced reduced evaporative cooling and carbon uptake, while the forests showed some resilience by increasing latent heat flux and carbon uptake. This event underscores the vulnerability of certain Australian ecosystems to climate change and the need for further research and monitoring to inform effective climate adaptation strategies.