Raindrops to Rivers: How watersheds influence ecosystems, lives, and communities

Everybody on the planet lives in a watershed. Even those in places that receive little rain, are land-locked, or located far from a source of water. Watersheds, or drainage basins, are seemingly invisible divisions of land that define the flow of water – from raindrops on hills to rivers in valleys – as it makes its way into reservoirs, bays, and the ocean. 

But watersheds are more than a way to understand how water moves. They shape fundamental processes that sustain the planet’s ecosystems and communities. Rivers, for example, create habitat and churn dams that power cities and irrigate crops. Reservoirs provide recreation and flood control. Watersheds govern the steady stream of freshwater that is essential to all life.

While watersheds may be everywhere, the world’s drainages are wildly diverse. The largest watershed, the Amazon River Basin, spans 2.7 million square miles, about 40% of South America. By contrast, a tiny mountain creek may flow in a watershed as small as a few square meters. Watersheds don’t always follow state or national borders, such as the Congo Basin that spreads over nine countries. What connects all these basins is (obviously) water – but not just what we see on the surface. Water also inches invisibly underground and recharges aquifers, or vaults into the air as a gas during evaporation, or is stored as mountain snowpack, flowing into streams as meltwater during warmer months. Water is in a constant cycle of coming and going, in both obvious and subtle ways. 

Watersheds are also vital to healthy landscape function, playing a crucial role in habitats, nutrient cycling, and overall environmental health. They support ecosystems such as wetlands and forests that both interact with and influence the freshwater cycle. Wetlands, for example, are nature’s filters: A single acre can typically store about one million gallons of water, cleansing water impurities and recharging ground water. Forests within watersheds help regulate when and how water flows, producing the highest quality water for human consumption. The interaction between water and forests can be profound and far reaching: tree restoration can affect rainfall patterns continents away (e.g., Amazon restoration impacts Europe and Eastern Asia). 

With so much importance on watersheds, it can be difficult to comprehend the many human threats to these systems – from land-use changes, to pollution. Here are a few of the most prominent impacts to watershed health:

• Land-use changes: Deforestation and replacement with impervious surfaces (roads, parking lots, buildings) increases runoff speed, flooding, stream bank erosion, and habitat loss. More than half of the wetlands in the continental United States are gone, and with them, vital storage areas and habitat. 
• Infrastructure impacts: Channelized rivers, dams and other engineered structures alter the flow of water and its ability to move sediment, build habitat, and clear pollutants. 
• Climate change: A warming world alters precipitation patterns and the tempo and timing of water flow. 
• The cascade effect: Put together, these impacts shorten water travel time to streams, increase peak flows, and cause water quality decline.

These threats are particularly acute in some of the world’s most critical watersheds. At Global Forest Generation, we support a network of skilled, passionate conservation experts working to protect the high-altitude watersheds of the Andes of South America. Here, an intricate dance of glacial melt, wetlands, fog, and forests influence water availability for millions of people downstream, including major urban centers such as Lima, Bogotá, Quito, Santiago, and La Paz, as well as for vital industries such as agriculture, hydropower, and mining. 

When the forests disappear and glaciers melt, watersheds lose their natural stability. Downstream rivers become more irregular, leading to longer and more intense droughts. Scientists estimate that the ice loss in the Andes could reduce the water flow to the Amazon River tributaries by up to 20%. 

Regenerating high-altitude wetlands and restoring forests locally helps ensure water for communities, preserves climate regulation, and protects the beauty and function of the Andes. And by protecting watersheds at their most critical points – the high forests and wetlands near where water begins its journey – we safeguard the invisible threads that connect mountains to valleys, raindrops to rivers. In these headwaters, every forest conserved and every wetland restored sends ripples across the continent and generations. 

If you care about watershed health and want to support our work in the Andes, visit: www.globalforestgeneration.org/donate/