A new study led by Flinders University aims to provide a good estimate of water used by trees and plants and bushes under the treetops (or in the forest ‘understorey’) to help improve management of native woodlands.
Researchers tested an advanced way to measure evapo-transpiration (ET) patterns in understorey (compared to canopy) vegetation at two different rainfall locations in South Australia to help develop better water and woodland management decision-making in future.
ET returns water from the soil and plants into the atmosphere and is the major component of terrestrial water balance, explains Professor of Environmental Science and Hydrology Huade Guan, from the National Centre for Groundwater Research and Training at Flinders University.
“Woodland understorey ET is difficult to monitor using conventional methods. Our latest study tested a new method of measuring understorey evapotranspiration in floodplains and catchment areas,” he says.
This is important to understand because understorey ET can contribute between 10% (in cooler seasons) and up to 50% (during hot weather) of ecosystem water use, researchers say.
The latest study, published in the Journal of Hydrology with collaborators from around Australia, China and the USA, retrieved understorey temperature from airborne thermal imagery and used it in a ‘maximum entropy production’ model (called the ‘MEP model’) to map understorey ET.
Researchers hope to improve ecosystem water evaluations to create more effective management strategies for increasingly scarce river and freshwater resources.
The research was based on investigations in a River Red Gum woodland of a Murray floodplain near Bookpurnong in the Riverland and a hilly woodland catchment near Mount Wilson in the Willunga Basin. The locations reflected different topographical, hydrological and climate conditions.
Both locations showed understorey ET was a key component of ecosystem water balance, so working out the best way to support River Red Gum and other woodland environmental water requirements could incorporate broadscale monitoring and mapping with high-resolution thermal data from satellites in future.
The study found that flooding modified water availability and vegetation response, influencing understorey ET dynamics over time, says Flinders University Professor Guan, who leads the Eco-hydrology and Hydro-meteorology Research Group (EcoH2OMe) at the College of Science and Engineering.
For example, after major flooding in 2022-23, the fraction of understorey ET to the total ecosystem ET declined, likely due to increased overstorey transpiration.
In the hilly environment, slope orientation plays a key role in regulating ET by controlling solar radiation exposure and soil moisture retention.
North-facing slopes generally have higher understorey ET than south-facing slopes, particularly in a wet winter, where understorey ET on the north-facing slopes accounts for up to 50% of total surface ET.
This high understorey ET on north-facing slopes consumes soil moisture a lot quicker, resulting in less water for vegetation use in dry summer than south-facing slopes.
The study highlights the advantages of integrating new methods and technologies in addressing environmental problems.
Meanwhile, South Australia is currently experiencing particularly dry weather, which is most likely the result of climate change, according to the SA Water for Good plan. This means less rain and a reduction of flows into traditional water sources such as our reservoirs, rivers and groundwater. The CSIRO has forecast an overall decline in rainfall of between 15% to 30% by 2050.
The SA Government plan emphasises the need for proactive management of non-prescribed water resources to ensure water security to 2050, including a deeper understanding of overall water resource capacity to prevent over-exploitation and enhance sustainability.
The article, ‘Integrating the Maximum Entropy Production model and airborne imagery for understorey evapotranspiration mapping’ (2025) by Wenjie Liu, Okke Batelaan, David Bruce, Jingfeng Wang, Hugo Gutierrez, Hailong Wang, Robin Keegan-Treloar, Jianfeng Gou, Robert Keane, Jessica Thompson and Huade Guan has been published in the Journal of Hydrology (Elsevier) DOI: 10.1016/j.jhydrol.2025.133076.
Acknowledgements: Field data were obtained in projects funded by Murray-Darling Basin Authority (MD005764) and National Centre for Groundwater Research and Training (SR08000001). Researchers acknowledge fieldwork by Karina Gutierrez, Lawrence Burk, Zhongli Liu, Zhechen Zhang, Xiang Xu and Rose Deng and landowners Langdon Badger and Steve Clark for access. Wenjie Liu received support from the China Scholarship Council (201906370006) and Jingfeng Wang’s research is sponsored by the National Science Foundation Hydrological Sciences and Physical and Dynamic Meteorology Program Grant EAR‐2006281.
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