At the Global Facility for Transboundary Waters, when we speak with stakeholders about transboundary water management, the conversation almost always centers on the stewardship of what is commonly referred to as “blue water,” water resources flowing in rivers, lakes, and aquifers. To be sure, these bodies of water are vital to human development, and their importance is evident, as approaches for sustainably governing blue water between countries have been decades in the making.
Yet, the focus on blue water overlooks water resources that are far more abundant, namely “green water”: the water that is stored in soil and vegetation and released back into the atmosphere as green water flows through evaporation and transpiration. Once airborne, this moisture travels vast distances, and mixes with evaporated blue water, before it precipitates and falls back to the earth as rain or snow.
Countries are not just connected through water flowing in rivers, lakes, and aquifers but also through these invisible atmospheric green water flows that travel across borders and continents. And how one country manages its land — whether it protects its forests, expands agriculture, or experiences ecosystem degradation — can impact rainfall and water availability in another country hundreds or even thousands of kilometers away.
Influence of forest and natural vegetation cover on green water flows and availability of water resources downwind. Source: Borgomeo et al. 2026. “Moisture in Motion: Integrating Green Water into Transboundary Water Governance and Development Finance.”
Recent reports from the World Bank Group, including Continental Drying: A Threat to Our Common Future and Reboot Development: The Economics of a Livable Planet, and from the Global Commission on the Economics of Water have mapped these atmospheric connections and quantified their importance for economic development and resilience. For example, green water flows from the Amazon Basin’s dense tropical forests generate up to 90% of rainfall in parts of South America, demonstrating the profound impact of green water flows on regional water security. The Reboot Development report shows that without these upwind forests, and the green water flows they generate, annual economic growth could decline by $11.4 billion in South America.
These figures underscore a straightforward but underappreciated truth: Protecting green water is not just an environmental imperative, but also an economic one, with consequences that reach far beyond national borders.
Recognizing the importance of green water flows opens new avenues for benefit sharing and cooperation. Countries can jointly invest in sustainable land and forest management, enhancing rainfall and water security not only locally, but also for neighboring regions and countries. As highlighted in the Continental Drying report, protection, conservation, and restoration of natural habitats is crucial to maintain green water recycling and drought resilience at multiple scales.
Recently, the Global Facility for Transboundary Waters invited river basin organizations, development partners, and academics to explore what it would take to integrate green water into transboundary water governance frameworks, first at the 2nd Global Forum on Transboundary Waters in June 2025 in Geneva (co-hosted with the Swiss Agency for Development and Cooperation and the UNECE Secretariat of the Water Convention). This was followed by discussion at the World Bank Group’s Law, Justice and Development Week 2025, and at the latest virtual Basin Roundtable hosted by the Global Facility in April 2026. These conversations showed us that more work is needed to deepen the collective understanding of the importance of green water for transboundary water management as well as of the transboundary nature of green water flows.
The Four Pathways Forward: How Countries Can Partner to Unlock the Benefits of Green Water
Building on these events and reports, with the support of the Global Water Security & Sanitation Partnership (GWSP), the World Bank Group recently published “Moisture in Motion: Integrating Green Water into Transboundary Water Governance and Development Finance.” This guidance note advises that unlocking the benefits of green water requires integrated approaches that link blue and green water management. Organizations like the Amazon Cooperation Treaty Organization are already pioneering these approaches, demonstrating the value of robust data sharing, regional collaboration, and sustained investment. The guidance note puts forward four recommendations to advance inclusion of green water in transboundary water governance and financing frameworks.
- Invest in the protection, management, and restoration of ecosystems with high green water and biodiversity value, especially old growth, or primary, forests and critical habitats that sustain regional and global green water flows.
- Mobilize existing institutional frameworks, including river basin organizations, for intra-basin green water governance and explore new approaches for cross-basin green water governance.
- Mobilize finance, leverage incentive-based instruments, and integrate green water indicators into existing financing frameworks.
- Invest in advancing knowledge and capacity for managing green water, including through inclusion of green water resources in water security assessments and water accounting at multiple scales.
As land-use pressures intensify and continents dry, the need for integrated and forward-looking transboundary water management becomes ever more critical. By integrating green water flows into traditionally blue water–focused transboundary water management practices, we can build a future in which water management and cooperation is grounded in the full reality of our interconnected world, and in doing so, enhance water security and shared prosperity for all.
Source : World Bank
