Why Cities Need Forests to Manage Their Water

But the forest’s job doesn’t stop at just helping generate rain.

After the rain comes tumbling down, trees stabilize the soil and prevent erosion. The root systems of forest vegetation maintain the forest floor, ensuring sediment and other materials aren’t swept into city water systems.

Without this natural filtration, water flowing out of the taps would be filled with runoff, requiring excessively expensive treatment plants to make the water drinkable.

For example, wildfires in Colorado during the late 1990s and early 2000s destroyed important watersheds, resulting in over $25 million in clean up costs to Denver’s water utility. Denver has since invested in protecting those forested watersheds from wildfires and degradation. You can also learn more about our tree planting projects in Colorado.

As you may know, trees help to clean water and forests take on all that water they play another vital role for cities: flood control.

Not only are the trees root systems filtering out pollutants, they are also slowing down the flow of water towards creeks, rivers, lakes, and ultimately cities. Forests require a lot of water to grow, so as rainwater soaks into the soil trees absorb substantial amounts through their roots. This uptake slows water down, stopping it from crashing downstream and flooding cities along the way.

Chopping down large swaths of trees to make way for other land uses makes water absorption impossible and creates a much higher risk of flooding.

Few places have experienced this worse than Jakarta, Indonesia. Fifty percent of Jakarta’s main watershed has been converted to agricultural land or urban development. Without the trees to stop it, throughout the rainy season water fills the many rivers running through the city of more than 10 million people, forcing many to evacuate their homes. You can help the environment by planting trees in Indonesia.