Bogotá, Colombia is in the throes of a water crisis.

After several months of dry weather caused by El Niño, the Chingaza reservoir system, which provides 70% of Bogotá's water, reached its lowest level in history. The city's over 8 million residents are now rationing water, with each neighborhood facing a 24-hour water shut-off three times per month. People are encouraged to shower for less than three minutes, and households are facing fines of up to $300 if they go over their monthly water allotment. Rationing measures will likely remain in place through October 2024, or until there is enough rainfall to course correct.

Bogotá is not alone; it is the latest in a string of cities dealing with extreme water scarcity. Mexico City currently faces the possibility of taps running dry in as little as a few weeks. Cape Town, South Africa famously staved off a "Day Zero" in 2018, in which the entire city nearly ran out of water after a rare drought.

More cities will likely face these kinds of shortages as climate change, deforestation and ecosystems degradation increasingly threaten the natural systems that maintain water supplies. But nature offers solutions, too.

By protecting, restoring and sustainably managing forests within their watersheds, cities can improve water quality and quantity in a cost-effective way. And they can make water sources more resilient to a changing climate.

Water Faces a Double Threat from Climate Change and Land Degradation

Climate change continues to raise global temperatures and cause unpredictable weather patterns. As climates become drier and rainfall becomes more erratic, water sources are less able to maintain a consistent supply and reliably replenish.

Bogotá, for example, has seen significant decreases in precipitation since 1971, leading to the water challenges facing the city today. In the Horn of Africa, over 20 million people are affected by drought across multiple countries. Two of these countries, Eritrea and Djibouti, face high levels of water stress, meaning they regularly use 40%-80% of their available water supply. Research suggests that the region's drought was made 100 times more likely because of climate change.

A dry reservoir with just a trickle of water at the bottom.
The San Rafael reservoir, part of Bogotá's main reservoir system, on April 8, 2024, after being severely depleted by drought. Water shortages are becoming more common as climate change disrupts the water cycle. Photo by Long Visual Press/Alamy Live News

Deforestation around watersheds is also a major driver of water insecurity. Forests support and improve water supplies in a few key ways:

  • Better infiltration: Root systems and fallen leaves in a forested watershed slow down rainfall, allowing more water to enter the soil. This supports more reliable and consistent groundwater recharge.
  • Less erosion: Because forests can slow down rainfall, the top layers of soil are better protected. Forest roots also create a strong foundation that helps keep soil in place. Both features reduce erosion, preventing debris from entering watersheds and reducing the need for water treatment and/or reservoir dredging.
  • More regular precipitation: The water cycle relies on water reaching the atmosphere through evaporation (when water is pulled from water surfaces and soil) and transpiration (when water is pulled from plant leaves, stems and flowers). Forests support both in the combined process of "evapotranspiration." This allows for a more regular water cycle and, therefore, more regular rain to recharge groundwater and fill watersheds.

In the United States alone, 180 million people rely on forested lands for their drinking water, with some cities relying on national forests and grasslands for almost 90% of their water supplies. Halting deforestation, particularly around water sources, is therefore critical to a reliable and sustainable water supply. Unfortunately, the opposite is happening: In 2023, the world lost 3.7 million hectares of tropical forests alone, equivalent to ten football fields per minute.

Graphic showing how forests protect and improve urban water supplies.

How Can Cities Use Nature to Improve Water Security?

As the threat of water shortages continues to spread, natural infrastructure can play a crucial role in improving water security for cities around the world.

Also called "green" infrastructure, these solutions leverage natural processes to fulfill infrastructure needs and build resilience to climate impacts. For example, restoring forest areas within a watershed can reduce the risk of flooding while also improving water quality and regulating water flows, helping to increase the amount of water available. Proper watershed management, including the removal of water-sapping invasive species, can also boost water quality and quantity. These kinds of nature-based solutions can complement traditional "gray" infrastructure (such as reservoirs).

There is a strong economic case for natural infrastructure, too. WRI studied the economic and water benefits of combining natural and traditional infrastructure in five cities across Brazil as well as in Bogotá. Every analysis showed that natural infrastructure can yield significant water benefits for cities while also producing cost savings for water utilities. In Bogotá, for example, the water utility could save approximately $45 million over 30 years by investing $5.3 million upfront in nature-based solutions such as ecosystem restoration.

Oftentimes, these savings come from reducing sedimentation and nutrients in water. This can reduce costs from "dredging" to remove sediments and from wear and tear on traditional infrastructure. It can also lower water treatment costs through reducing the need for chemical products and decreasing the amount of energy used to pump and distribute water across a plant for treatment.

4 Ways Cities Can Leverage Natural Infrastructure for Water Security

While natural infrastructure can certainly benefit city water supplies, the right approach will vary from place to place. So, what does this look like in practice? Four cities working with WRI's Cities4Forests initiative show the possibilities:

High-altitude Grassland Restoration in Bogotá, Colombia

While the latest water crisis in Colombia is new, the need for better water infrastructure is not. Recent research from WRI Colombia, Conservation International Colombia, and Bogotá's water utility showed that natural infrastructure could play an important role in diversifying the city's water sources, saving money for the local water utility and ultimately improving water security for the city.

There are significant opportunities for natural infrastructure in the city's nearby páramos, or high-altitude grasslands. These include ecosystem restoration and silvopastoral systems, which combine tree growth and livestock production on the same land. Implementing such solutions across just 2% of the Bogotá River's upper basin, the second largest water source for the city, would help reduce the presence of sediment in the water and save the local utility money on treatment.

Improvements to water quality would also make the Bogotá River basin a more reliable water source, allowing the city to diversify its water supply. This would make Bogotá less reliant on the Chingaza reservoir system and more resilient to drought and other threats.

River Basin Reforestation in Vitória, Brazil

The mountainous state of Espírito Santo, Brazil is no stranger to droughts. The state's four million residents, half of which are in the greater Vitória metropolitan area, have faced severe droughts for over a decade. In 2015 alone, Espírito Santo experienced half of its average historical rainfall. Meanwhile, more erratic rainfall patterns driven by climate change have also led to intense flooding across the nation, with recent floods affecting over half a million people in Porto Alegre.

But there is an opportunity to improve water security and reduce flood risk using natural infrastructure in two main water sources for Vitória: the Jucu and Santa Maria da Vitória river basins. Our research showed that reforestation across 2,500 hectares of degraded land would improve water security and save the local water utility money through reduced sedimentation. This is significant, as the water utility provides water and sanitation to over 70% of Espírito Santo. In the Jucu River alone, restoration could prevent 40 dump trucks worth of sedimentation from reaching the river every year. And because trees can intercept and slow rainfall as it lands, reforestation efforts can also reduce flood risks.

Following this analysis, Espírito Santo adopted a law to prioritize restoration in many of these upstream areas. The state also replicated the study for other watersheds.

Two men load seedlings onto a truck bed in the rainforest.
Two men load seedlings onto truck for a reforestation project in Rio de Janeiro, Brazil, to the south of Vitória. Increased reforestation efforts within watersheds throughout Brazil could help improve water security while also reducing the risk of flooding. Photo by Cavan Images/Alamy Stock Photo

Restoration of the Nairobi River in Kenya

Nairobi is deeply intertwined with its river systems: The city name itself comes from the Maasai phrase for "cool waters." However, many interconnected issues are affecting the Nairobi River. Kenya faced the most severe drought in the nation's history over the past few years, and rapid urbanization and population growth have led to significant water pollution.

In early 2023, the Nairobi Rivers Commission launched a plan to rejuvenate and restore the Nairobi River. The commission and its partners are currently working to identify priority areas for restoration and find ways to integrate nature-based solutions, such as reforesting areas along the river, into urban planning.

These efforts will help reduce pollution and improve access to clean drinking water for the city's over 4 million residents — only half of whom currently have access to water from pipes. They will also create new job opportunities in wetland management, particularly for the city's youth. And they will increase access to hydroelectric power in rural areas. This is critical, as 12 million people in Kenya currently do not have energy access. The project will also support Kenya's goal to grow 15 billion trees by 2032.

In addition to water quality efforts, priority areas for restoration are being identified to reduce flood risk in Nairobi. This is also an urgent issue, as devastating floods in Kenya have recently claimed the lives of over 200 people and displaced almost a quarter of a million more.

Natural Wastewater Treatment in Delhi, India

India is among the most water-stressed countries in the world. The nation holds 18% of the world's population but only 4% of its water. It is also the world's largest user of groundwater and is facing declines in groundwater levels across almost two-thirds of its districts. Many of its main water reservoirs are hitting record-low levels. In addition, over 70% of the nation's wastewater is untreated and flows into natural water sources, leading to significant water pollution.

TheCityFix Labs, an initiative by Cities4Forests and WRI India, is supporting two local projects to scale up their nature-based solutions that can address these interconnected issues.

The first, BacTreatEnvironmental Solutions, is using constructed wetlands to manage wastewater. These use wetland plants and soil to mimic a natural wetland, which captures stormwater and creates micro-habitat for plants and birds. The second, Padma Clean Environs, created a sustainable drainage system that cleans wastewater naturally using vegetation and then filters it into engineered soil, allowing the water to soak into the ground more effectively. This approach enables groundwater recharge with no negative environmental effects, costs significantly less than other recharge systems, and can easily be used across the city since it does not require large areas of land.

Carving a Path for Natural Infrastructure

Bogotá, Mexico City and Cape Town may be among the most prominent examples of water insecurity in recent memory. But climate change, population growth and ecosystem degradation are likely to push many others into the same situation.

Cities facing current or future water shortages can learn from those already implementing natural infrastructure to improve water security and prevent further land degradation. And they can take immediate steps to better integrate nature-based solutions into urban planning and climate action.

Cities do not need to choose between water security and nature. With the right projects in place, collaboration from the right people, and strong investments, the cities of Bogotá, Vitória, Nairobi and Delhi can go from being an exception to being some of the first in a new norm.