Integrating Green and Gray

The report argues that combining natural systems—such as forests, wetlands, and mangroves—with built infrastructure can lower costs and increase resilience against climate change. It provides a technical, social, and economic framework for project appraisal and highlights the need for enabling policies and innovative financing to mainstream these 'next generation' infrastructure solutions.

• Traditional gray infrastructure alone is insufficient to meet 21st-century needs, with global financing needs for water supply infrastructure estimated at US$6.7 trillion by 2030 and $22.6 trillion by 2050.
• Integrating green infrastructure can reduce the capital and operational costs of gray infrastructure. For example, New York City saved 22 percent, or $1.5 billion, by combining green and gray strategies for its water supply instead of using a gray-only approach.
• Green infrastructure can enhance the lifespan and performance of built assets; for instance, protecting upstream watersheds reduces sediment inflows that would otherwise cause wear and tear on hydropower plants and reduce reservoir capacity.
• The technical performance of green infrastructure is often more probabilistic and adaptive than the deterministic models used for gray infrastructure, requiring a different approach to risk and uncertainty management.
• Green infrastructure typically has a larger land footprint than gray infrastructure, making community buy-in and land-use agreements critical for project viability.
• Because green infrastructure provides environmental and social cobenefits, it can attract funding from mission-driven investors, grants, and green bonds that traditional gray projects might not access.
• A 'pay-for-success' or environmental impact bond model, as used in Washington, DC, can share performance risks between the service provider and investors, rewarding investors if the green infrastructure exceeds runoff reduction expectations.
• Policy barriers often hinder the adoption of green infrastructure, such as jurisdictional spending restrictions that prevent agencies from funding projects that cross administrative boundaries but follow ecosystem lines.
• In Peru, a 2016 Sanitation Sector Reform Law requires water utilities to earmark revenue from tariffs for watershed conservation and climate change adaptation.
• The World Bank approved at least 81 projects with green infrastructure components between 2012 and 2017, with the highest concentration of these projects located in Africa and East Asia and the Pacific.

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_0.pdf?_ga=2.227204765.1275636092.1560182901-735189898.1502292474

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_0.pdf?_ga=2.227204765.1275636092.1560182901-735189898.1502292474.

Wikipedia

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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_0.pdf?_ga=2.227204765.1275636092.1560182901-735189898.1502292474}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }