Earth's largest remaining tract of tropical rainforest is kept alive by a complex water cycle that we're only just beginning to understand. Yet our activities are changing it before we can see the full picture, a new report finds.

The rivers and tributaries of the Amazon rainforest hold around a fifth of Earth's fresh water, nourishing a stunning variety of mammals, birds, plants and amphibians. It also helps support the 47 million people in the surrounding basin region which includes mountain forests, wetlands, and river systems across nine South American countries.

The complex hydroclimatic system that sustains this region interconnects over the Andes mountains, Amazon lowlands and Atlantic Ocean (the AAA pathway), cycling water molecules from Earth's surface into the air and back again. Researchers have previously compared this system to a pump that recycles moisture, supporting regional rainfall.