Daniel Henryk Rasolt writes:

High in the Andes Mountains, the mighty Amazon River begins. It trickles from glaciers and oozes from mountain wetlands. It gains momentum and volume and feeds into clear streams and muddy rivers that pass through high cloud forests and lowland valleys. The torrents of the waters carry nutrients through the vast Amazon River basin, some 4,000 miles across the rest of the South American continent.

At the same time, in the rainforest and delta estuaries, another, more ethereal—but no less essential—river is forming.

Across the Amazon rainforest, water is being sucked up by plant roots, transported through their bodies, and emitted or “transpired” from their leaves. In the air, this vapor rises and cools, condensing into clouds. Thus suspended, it becomes a sort of “flying river” of water vapor, flowing west, back toward the Andes. Along its own winding journey, its contents will fall as precipitation, forming upland rivers, wetlands, and mountain snow and icepack to feed, once again, the Amazon.

This interconnected cycle has been a sustaining force for some 10 million years. But the system appears to be faltering.

With tropical Andean glaciers quickly receding and high Andean wetlands threatened by climate change and unsustainable land use, the headwaters of the Amazon River are at risk. Its tributary rivers are being fragmented and depleted. Below, deforestation and land degradation in the Amazon basin are reducing the number of water-transpirers and threatening the westward flow of precipitation that ultimately forms the terrestrial river’s sources.

If this cycle breaks down and decouples, it could have profound implications for regional and potentially even global water cycles and climate, as well as for the biological and cultural diversity across much of the continent. [Continue reading…]