The role of trees in the water cycle
Friday 8th of May 2020
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Greenfleet's forest called Wurneet Laang Laang

Trees are remarkable at sequestering carbon from the atmosphere through the process of photosynthesis, but they also play a vital role in the water cycle and improving water quality.

Along with oceans, forests have an equal part in creating rain through the transpiration and evaporation from their leaves. Imagine each tree as a fountain, withdrawing water from the ground and perspiring it into the air. When a forest of trees does this together, it can have a hugely beneficial impact on our world.

Water purification

Almost like a natural filtration machine, a tree is designed to hold and clean water. Acting like a sponge, trees can filter out impurities in water before it passes back out through their leaves or roots. The debris of trees also becomes a part of the process as decomposing leaves form soil and provide the structure for natural water filtration to occur.

In many of Greenfleet’s projects, our restoration of native vegetation has helped improve water quality in systems such as creeks, rivers, and dams.

On a recent visit to our forest called Wurneet Laang Laang, which was first planted in 2016, our team found that the Lang Lang River was benefiting from the trees planted on the property. They also noticed that native frogs have started calling the dams on the property home and that there are now native reeds and ferns growing back.

This improvement in water quality can be especially important following events such as the recent bushfires that devastated many parts of Australia. With billions of wildlife perishing through the event, the Australian Government identified 119 priority species [1] that had been most heavily impacted. Of these, more than 50% were freshwater species who can be impacted by increases in water temperatures and ash travelling into waterways as a result of the fires [2].

Cooling effects and the distribution of water resources

Trees have a pronounced cooling effect on our planet that goes beyond providing shade for wildlife and people. The transpiration and evaporation of the moisture in trees and other vegetation is known as evapotranspiration [3] and this process can cause the atmosphere around the tree to cool. Depending on the location and species, a single mature tree can transpire up to 150 L of water per day and in a hot and dry climate like in Perth, Western Australia this can produce a cooling effect similar to two air conditioners running for 20 hours![4]

Evapotranspiration from forests and evaporation from oceans each make up roughly half of the world’s rainwater cycle. Where oceans account for most of the rain along the coast, forests can be responsible for a great majority of inland rainfall.

Tropical rainforests are at the heart of this process where transpiration is its most apparent. Did you know that the evapotranspiration from the Amazon can make it all the way to Midwestern USA? That is almost 6000kms! [5] This illustrates the importance of not only reforestation but also protecting existing and established forests from deforestation, which remains a problem in many parts of Australia.

Trees and forests play an integral part in the water cycles and quality that maintain the interconnected ecosystems on our planet. While Greenfleet’s focus is on taking climate action through capturing carbon emissions, there are also strong environmental co-benefits of our native reforestation efforts. We are constantly working toward taking critical climate action, helping to restore habitat for wildlife and helping to improving the quality of water.


[1] Australian Government, Department of Agriculture, Water and Environment [2] The Conversation [3] Australian Government, Bureau of Meteorology [4] CoastAdapt [5] Yale School of Forestry & Environmental Science