Forest Filter

Feb. 25, 2019

WQP Associate Editor Lauren Estes asked Suzanne Ozment about the connection between forest restoration and water supplies in Sao Paulo

About the author:

Suzanne Ozment is associate for the World Resources Institute, Global Water Program. Ozment can be reached at [email protected].


In 2014, the city of São Paulo faced a water crisis during which reservoirs held only 5% of their capacity, a situation echoed in last year’s Cape Town, South Africa, Day Zero crisis. A new report from the World Resources Institute (WRI) explored the connection between forest restoration and water supplies in São Paulo, and ultimately found the green practice could provide a return on investment for water companies. WQP Associate Editor Lauren Estes asked Suzanne Ozment, the report’s lead author, about the study and its potential global applications. 

Lauren Estes: How is São Paulo uniquely vulnerable to a water crisis?

Suzanne Ozment: São Paulo is a unique city, but the water crises it has faced are increasingly common in large cities around the world. Poor water quality that makes treatment more expensive, floods and droughts between dry and wet seasons, and a vastly growing population all make it challenging to supply clean, abundant water. The challenge is exacerbated by the city’s inadequate infrastructure: over 20% of São Paulo’s treated water is lost through leaky pipes. Like many cities, São Paulo will become more vulnerable to water crisis due to climate change and deforestation of forests near and far.

Estes: How can forest restoration benefit an overtaxed drinking water system? 

Ozment: Restoring forests upstream of a city can improve water quality and, in some cases, also boost water quantity. A healthy forest acts as a water filter by capturing sediment and acts like a sponge by storing water during wet seasons and releasing it during dry ones. In São Paulo, we found that that restoring 4,000 hectares (nearly 10,000 acres) of these forests could reduce sediment pollution by 36% within 30 years, reducing turbidity by almost half and potentially boost water supply during the dry season. This translates into water treatment cost-savings for water utilities, and reduces wear and tear on equipment such as hydropower turbines. For São Paulo, restoring those 4,000 hectares could avoid $106 million in water management costs over 30 years.

Estes: What other benefits can forest restoration provide?

Ozment: Healthy forests provide many benefits to a watershed and the citizens who live in and around it. Restoring a forest can reduce wildfire risk, create jobs and boost tourism. Forests improve air quality and capture and store carbon, preventing climate change. They offset the urban heat island effect in cities. Forests also support many livelihoods—from fishing to logging—as well as provide refuge for those who recreate in them.

Estes: How did you calculate restoration benefits?

Ozment: While the values of natural infrastructure have long been understood in a qualitative sense, water sector investors still struggle to understand the financial rationale for investment, and are likely missing opportunities to improve service delivery by overlooking the financial value of natural infrastructure. WRI’s Green Gray Assessment method provides a tool to overcome that challenge. The study used this method to evaluate the financial performance of alternative natural infrastructure investment options over 30 years. It allows water-dependent companies and water sector investors to examine the costs and benefits of utilizing green infrastructure in combination with traditional grey infrastructure, and can be replicated across geographies. It links forest to a return on investment for water companies, yielding decision-relevant information for stakeholders.

Estes: Is this study applicable to other cities?

Ozment: WRI and partners have already used the Green Gray Assessment in several U.S. cities, as well as Rio de Janeiro and Vitoria, Brazil, and Monterrey, Mexico. It is our hope that more researchers will adopt these methods and use the Green Gray Assessment to uncover the potential benefits of forest restoration for water in their communities.

Estes: How can utilities and cities finance forest restoration?

Ozment: Financing is often a barrier for water infrastructure development, but it opens new opportunities when natural systems like forests are included in project plans. For example, when healthy forests control sediment pollution and reduce the burden on the water system, those cost savings can alleviate overstretched water management budgets. ... We are also seeing that green infrastructure can attract mission-driven impact investors and even sometimes foundations to co-invest with cities and utilities to provide cleaner water while also helping communities adapt to climate change and protect biodiversity. 

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