Green‑to‑Blue Ratio (G/B)

The Green-to-Blue Ratio (G/B) is an indicator that expresses the proportion of green water (rainwater stored in soil and used on-site by crops or vegetation) relative to blue water (surface water or groundwater extracted for irrigation) used in agricultural or industrial processes. A high G/B value indicates greater reliance on rainfall and therefore lower pressure on freshwater resources such as rivers and aquifers.

Formula

G/B = green water footprint divided by blue water footprint.

Applications

• Agriculture: assessing the sustainability of crops (for example wheat compared with rice).
• Basin planning: promoting practices that enhance rainwater infiltration and green-water retention.
• Corporate strategies: identifying suppliers with a lower blue water footprint to reduce operational risk in water-stressed areas.

How to improve the G/B ratio

• Soil conservation: cover crops and minimum tillage to retain soil moisture.
• Crop selection: varieties adapted to local rainfall patterns.
• Rainwater harvesting: rooftops, micro-catchments and terraces that increase infiltration.
• Irrigation efficiency: systems that minimise evaporation and leaching losses.

Advantages of the indicator

• Simplicity: a clear, easily communicated metric.
• Action-oriented: it encourages conservation-agriculture practices.
• Complementary value: it adds context to standalone blue and green water footprints.

Limitations

• It does not capture water quality or the seasonality of rainfall.
• Spatial variability: results should be interpreted at basin or field level for accuracy.

The Green-to-Blue Ratio is a quick, practical guide for assessing and improving water sustainability, helping to reduce pressure on blue-water sources in vulnerable or water-stressed regions. At Manglai we help companies measure their water and carbon footprint and prepare their sustainability reporting. Discover how Manglai can help you.