How Forests Help Cities to Manage Water

Joseph Coppolino | March 07, 2019 | 4 min read


Go to your kitchen sink and open the tap. If you can take a glass, fill it with cool crisp liquid from the faucet, and take a nice big gulp you can likely thank trees for that refreshing drink of water.

Cities often have intricate water systems to ensure you have access to clean water. But at the very beginning of all the pipes and pumps lies a forest: trees help to clean the water.

New York City is a great example of making the most of nature. The city saved money by conserving and restoring the Catskills/Delaware watershed, which supplies 90% of its water. By investing some $1.5 billion to protect the forested watershed, the city avoided building a water filtration plant and saved between $6-8 billion dollars.

Forests help to provide clean water

A third of the world’s largest cities rely on protected forests for their water. And with a rapidly growing and urbanizing global population, that number will only increase in the future.

How do forests help cities?

1. Forests Provide Water

A forest’s first role in managing a city's water comes from the vapor produced by its trees and vegetation. Water captured, stored, and released by forest canopy is an important factor in regulating precipitation and the evaporation of groundwater.

Forests create rainfall that flows downstream and supplies cities with fresh water!

Unfortunately, if forested watersheds become degraded, the regularity of precipitation is thrown off and rainfall becomes less predictable, leading to fluctuating periods of flooding and drought.

The impact of deforestation on a city’s water supply became abundantly clear in Brazil just four years ago. Riots broke out in Sao Paulo and the surrounding municipalities when a record-breaking drought brought reservoir levels down to just 5% - only a months supply for an area with more than 21 million people.

The drought has been blamed on large-scale deforestation to make room for agricultural production taking place in the nearby Amazon rainforest. Without the trees to regulate precipitation, Brazil’s biggest city nearly found itself without any water at all.

Deforestation impacts global water supply too. Cutting down trees hurts those living nearby the most, but scientists believe that widespread deforestation in the Amazon could impact areas as far away as California, and even Africa, regions already plagued by droughts.

Forests filter water

2. Forests Filter 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.

Forests control water

3. Forests Control Floods

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.

Seagulls on beach
Woman relaxing on hammock
Owl in field of flowers

Why cities need forests

Despite being surrounded by pavement, skyscrapers and all necessary amenities, life in the city is drastically improved by the existence of all types of forests, both near and far. They provide potable water, reduce utility costs, and can even save people's lives and livelihoods.

And these are just a few ways forests benefit cities, but forests provide much more to urban and rural communities everywhere. Trees clean the air we breath, provide innumerable health benefits, and support biodiversity.

So if you want to continue getting fresh water from your tap make sure you are protecting forests any way you can and learn more about the Cities4Forests initiative to get involved in your own city! Looking to do more? Plant a tree with us today!

Plant Trees Where They're Needed Most
Plant Trees Where They're Needed Most
Plant Trees Where They're Needed Most
Plant Trees Where They're Needed Most
Plant Trees Where They're Needed Most
Plant Trees Where They're Needed Most
Plant Trees Where They're Needed Most
Plant Trees Where They're Needed Most
Plant Trees Where They're Needed Most
Plant Trees Where They're Needed Most
Plant Trees Where They're Needed Most
Plant Trees Where They're Needed Most
Plant Trees Where They're Needed Most
Plant Trees Where They're Needed Most

Plant Trees Where They're Needed Most

As the need for reforestation is global and ever-changing, we feature where trees are most needed now. Today, we're raising funds to jumpstart forest fire recovery in British Columbia. Learn more

With your help, we will:

  • Restore landscapes damaged by a historic season of wildfires
  • Create habitat for iconic biodiversity like the moose and grizzly bear
  • Support old-growth management areas to maintain complex ecosystems
  • This reforestation initiative is helping to restore the landscape in British Columbia after the Hanceville fire burned over 590,000 acres in 2017 and natural regeneration has not occurred. The fire has impacted the forest, soils, riparian ecosystems, wildlife, and water quality. Local indigenous communities have seen their ability to hunt and gather food drastically altered. But your support will go a long way! The goal of planting trees here is to not only re-establish a healthy forest, but also to plant species that will be resilient in the face of climate change. Thank you so much for your support of healthy forests! 🌲
  • Planting trees will catalyze the process of returning the area to a forested state. Newly planted trees will begin the process of sequestering atmospheric carbon, and over time improve the hydrological benefits of the forest. The ecosystems that have been greatly simplified by extreme fire conditions will once again become complex ecosystems, This project will also create habitat for many local wildlife species including mule deer, moose, black and grizzly bear, wolves, sandhill cranes, various raptors, songbirds, and small mammals.
  • A personalized tree certificate (see gallery) to say thanks for your donation. We'll also send you updates about this project, so you can track the impact your trees are having on the community and environment.
  • B.C.'s rich forest diversity includes more than 40 different species of native trees, with some of Canada’s most interesting and valuable tree species. In this project, we made efforts to maximize species diversity, including the following species: Douglas-fir, lodgepole pine, hybrid spruce, ponderosa pine, trembling aspen.

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