Rivers in the sky: the devastating effect deforestation is having on global rainfall
The world’s forests are a source of water, influencing precipitation over huge distances. The loss of the moisture recycling from cutting them down could be a more imminent threat even than global warming
Gérard Moss is a bush pilot in the swashbuckling tradition. Born in Britain and raised in Switzerland, he had flown twice round the world in his single-engine plane before he set out on a new journey, to track rain clouds across the Amazon in his adopted home of Brazil.
Local scientists had an idea: that the forests of the Amazon were the continent’s biggest rainmakers; that most of the moisture in the clouds had been taken up and recycled back into the air five or six times by its 400 billion or so trees.
Take away the trees, reasoned biologists such as Antonio Nobre, then of the National Institute of Amazonian Research in Manaus, and the rains would die. The Amazon basin would turn to desert. But with the rainforest largely a black hole for meteorological data, the idea was just that – until they hired Moss to equip his plane to collect water vapour.
People once said that rainforests had high rainfall because they were located in wet parts of the world. Now it looks like forests usually make their own rainfall
His data showed that the jet carried enough water in a day to supply the 20 million inhabitants of the metropolis for almost four months. Isotopic analysis revealed that most of that water had been generated by the rainforest. The role of forests in the world’s water supplies was starting to come into focus. Alarm bells would soon be ringing.
We now know that flying rivers traverse the globe and influence rainfall over huge distances. And we are learning that forests play a key role in supplying them, which means that, in much of the world, the loss of the moisture recycling from deforestation is a more imminent threat even than global warming.