Everyone knows rainforests are the lungs of the Earth. But they are also the heart of the world’s water system. And rainforests without rain are a threat to our planet’s future.
Rainforests drive the flow of water as rain at a global level. They are the centre of the water cycle, pumping air and water, circulating water vapour, and feeding rivers that eventually take water back to the oceans. Evaporation from the oceans is seeded by organic dust and particles created by the trees themselves. It is a remarkable system, working simultaneously at microscopic and planetary levels, full of intricacies and interdependencies.
As we’ve begun to understand more about how this relationship works, we’ve also started to understand the effects of deforestation on rainfall. One study found that since 2000, some 69% of the Amazon rainforest received less rain than before. Deforestation is undoubtedly a factor as less condensation occurs over forests with fewer trees. Not only is there less water to circulate within the Amazon basin, but less that can then be circulated outside it.
The impact that deforestation is having on the world’s water system is not simply a theoretical future risk. It has been suggested that in the Amazon, 30 – 50 % deforestation would be the tipping point for a complete change in state of the system.. Over the last 40 years, 20% of the Amazon rainforest has been destroyed.
By removing the forests in the equatorial latitudes, we are also allowing the land to absorb more heat, elevating air temperatures and further upsetting the water cycle. Just like the polar ice caps, tropical rainforests actually reflect heat back into space. This is called the albedo effect.
Lack of rainfall, combined with higher temperatures, has made rainforests more susceptible to man-made fire. There’s also research that suggests lightning strikes are increasing in rainforest, sparking further fires in arid areas.
Those who live on the front lines of climate change cannot afford to wait. Trees protect communities from flooding, provide them with food and housing materials, and mitigate climate change on a global scale. Without them, life as we know it will not be the same.
The global water system has rainforests at its heart. And if that is under pressure, the consequences will reach everyone.
Juniper, T, Rainforest: Dispatches from Earth’s most vital frontlines. 2018