Integrating Green and Gray

The report argues that traditional 'gray' infrastructure alone is insufficient to meet global development goals and climate adaptation needs. It proposes a 'next generation' approach that combines built solutions with 'green' systems—such as forests, wetlands, and mangroves—to improve water supply, flood management, and hydropower efficiency. The authors provide a framework for evaluating these projects across technical, environmental, social, and economic dimensions, emphasizing that green infrastructure can lower costs, increase resilience, and empower local communities if rigorously designed and supported by enabling policies and innovative financing.

• Traditional built infrastructure is insufficient to address escalating environmental threats and financing gaps. Global water supply infrastructure needs are estimated at US$6.7 trillion by 2030 and $22.6 trillion by 2050, which significantly exceeds current financial flows.
• Integrating green infrastructure—such as watersheds, wetlands, and mangroves—with gray infrastructure can enhance system performance and reduce costs across multiple sectors, including water supply, hydropower, coastal and river flood protection, and agriculture.
• Green infrastructure offers technical advantages in resilience and adaptability, though it introduces higher complexity and uncertainty compared to gray infrastructure. For example, in Poland, combining multipurpose flood retention areas with traditional embankments can protect against 1,000-year floods.
• The success of green infrastructure is heavily dependent on its social dimension, as local communities often act as the primary operators and stewards of natural systems. This creates opportunities to reduce social inequality but requires higher social transaction costs than traditional projects.
• Green-gray integration can lead to substantial financial savings. A notable example is New York City, which saved 22 percent, or $1.5 billion, by utilizing a combined strategy for its water supply instead of a gray-only approach.
• Scaling green infrastructure requires specific enabling conditions, including supportive laws and innovative financing. Examples include Peru's law requiring water utilities to earmark revenue for water conservation and the use of 'water funds' in Quito, Ecuador, to finance watershed protection.

APA

Browder, G., Ozment, S., Bescos, I. R., Gartner, T., & Lange, G.-M. (n.d.). Integrating Green and Gray. World Resources Institute. https://wriorg.s3.amazonaws.com/s3fs-public/integrating-green-gray-executive-summary.pdf

Chicago

Browder, Greg, Suzanne Ozment, Irene Rehberger Bescos, Todd Gartner, and Glenn-Marie Lange. Integrating Green and Gray. World Resources Institute, n.d. https://wriorg.s3.amazonaws.com/s3fs-public/integrating-green-gray-executive-summary.pdf.

Wikipedia

{{cite report |last1=Browder |first1=Greg |last2=Ozment |first2=Suzanne |last3=Bescos |first3=Irene Rehberger |last4=Gartner |first4=Todd |last5=Lange |first5=Glenn-Marie |title=Integrating Green and Gray |publisher=World Resources Institute |url=https://wriorg.s3.amazonaws.com/s3fs-public/integrating-green-gray-executive-summary.pdf |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{browderndintegrating, author = {Browder, Greg and Ozment, Suzanne and Bescos, Irene Rehberger and Gartner, Todd and Lange, Glenn-Marie}, title = {{Integrating Green and Gray}}, institution = {World Resources Institute}, url = {https://wriorg.s3.amazonaws.com/s3fs-public/integrating-green-gray-executive-summary.pdf}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }