Yes, it’s true… scientists have evidence supporting the widespread perception that trees make rain, that by growing more vegetation, we get more rain.
On average, 40% or more of the precipitation over land originates from evaporation and the transpiration of water from vegetation. Forests like the Amazon don’t merely grow in wet areas; they create and maintain the conditions in which they grow by increasing rainfall and reducing the length of the dry season.
Trees and forests increase rainfall intensity through the fungal spores, pollen, bacterial cells and other particles they release into the atmosphere. Atmospheric moisture condenses when the air becomes sufficiently saturated with water and does so much more readily when these particles are present.
When vegetation gets cleared, wet seasons come later, and less water is available in the landscape for evaporation and transpiration, suppressing precipitation.
The effects of Deforestation on Rainfall[7]
For example, more rain used to fall on the western side of a 750 km long fence built to exclude rabbits in southwest Australia. Today, however, the land on the eastern side of the barrier gets higher rainfall. This is because, on the western side, most of the vegetation has since been removed for arable cropping.
Cloud cover either side of the Rabbit-Proof Fence (©Earth Observing Laboratory)
Reliable rainfall in the continental interiors of Africa, Australia and elsewhere also appears to depend on maintaining relatively intact and continuous forest cover from the coast. How do we know this? Research demonstrates that for more than 60% of the tropical land surface, the air that has passed over extensive vegetation in the preceding few days produces at least twice as much rain as air that has passed over little vegetation. This transportation of moisture inland is called the Biotic Pump.
How to make Rain Happen!
It’s great to know that trees make rain, but trees are being cleared at a faster rate than at any time in history! How can we possibly reverse this? How can we get more rain?
Share this article showing the scientific evidence and help change the story we tell about the value of trees – everyone in your community will be out planting trees!
References for Trees Make Rain
[1] Shukla, J and Mintz, Y, 1982. Influence of Land-Surface Evapotranspiration on the Earth’s Climate Science19 Mar 1982: 1498-1501. Vol. 215, Issue 4539, pp. 1498-1501
DOI: 10.1126/science.215.4539.1498 (https://www.science.org/doi/10.1126/science.215.4539.1498)
[2] David Ellison, Cindy E. Morris, et al. 2017. Trees, forests and water: Cool insights for a hot world. Global Environmental Change 43 (2017) 51–61 (https://www.sciencedirect.com/science/article/pii/S0959378017300134)
[3] Jonathon S. Wright, Rong Fu, John R. Worden, Sudip Chakraborty, Nicholas E. Clinton, Camille Risi, Ying Sun, Lei Yin, 2017, Rainforest-initiated wet season onset. Proceedings of the National Academy of Sciences Aug 2017, 114 (32) 8481-8486; DOI: 10.1073/pnas.1621516114 (https://www.pnas.org/doi/10.1073/pnas.1621516114)
[4] Spracklen, D., Arnold, S. & Taylor, C. 2012, Observations of increased tropical rainfall preceded by air passage over forests. Nature 489, 282–285 doi:10.1038/nature11390 (https://www.nature.com/articles/nature11390)
[5] Nair et al-2011-Journal of Geophysical Research-Atmospheres (1984-2012) The role of land-use change on the development and evolution of the west coast trough, convective clouds, and precipitation in southwest Australia (https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2010JD014950)
[6] Charles Massey – Farming in the Middle East and Australia: lessons about a brittle climate. ABC Saturday Extra (https://www.abc.net.au/radionational/programs/saturdayextra/farming-in-the-middle-east-and-australia:-lessons-about-a-britt/10794674)
[7] Aragão, L. The rainforest’s water pump. Nature 489, 217–218 (2012) (https://www.nature.com/articles/nature11485)
