Transboundary water governance has traditionally focused on “blue water” — rivers, lakes, and aquifers — but recent work highlights the critical importance of “green water,” the moisture stored in soil and vegetation that cycles back into the atmosphere through evaporation and transpiration. These invisible flows travel across borders and continents, linking countries through rainfall patterns and water availability. How one nation manages its forests and land can directly affect rainfall and water security in another, sometimes thousands of kilometers away.
Reports from the World Bank Group and the Global Commission on the Economics of Water have mapped these atmospheric connections, showing their profound economic and ecological impact. For instance, green water flows from the Amazon Basin generate up to 90% of rainfall in parts of South America. Without these forests, annual economic growth in the region could decline by billions of dollars, underscoring that protecting green water is both an environmental and economic imperative.
Recognizing the role of green water opens new opportunities for cooperation. Countries can jointly invest in sustainable land and forest management to enhance rainfall and resilience, benefiting entire regions. Protecting and restoring natural habitats is essential to maintain green water recycling and drought resistance.
The Global Facility for Transboundary Waters has convened river basin organizations, development partners, and academics to explore how green water can be integrated into governance frameworks. Discussions at the Global Forum on Transboundary Waters in Geneva, the World Bank’s Law, Justice and Development Week, and recent Basin Roundtables highlighted the need to deepen understanding of green water’s transboundary nature.
Building on these dialogues, the World Bank Group’s guidance note Moisture in Motion outlines four pathways forward: investing in ecosystem protection and restoration, mobilizing institutional frameworks for intra‑ and cross‑basin governance, integrating green water indicators into financing, and advancing knowledge and capacity through water security assessments.
As land‑use pressures intensify and continents dry, integrating green water into transboundary water management is vital. By linking blue and green water governance, countries can strengthen resilience, enhance water security, and unlock shared prosperity across borders.
