Green‑to‑Blue Ratio (G/B)

The Green-to-Blue Ratio (G/B) is an indicator that expresses the proportion of green water (rainwater consumed on-site by crops or vegetation) relative to blue water (surface 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 / Blue Water Footprint

Applications

• Agriculture: assess the sustainability of crops (e.g., wheat vs. rice).
• Basin planning: promote practices that enhance rainwater infiltration and green water retention.
• Corporate strategies: identify suppliers with lower blue water footprints to reduce operational risks.

How to Improve the G/B Ratio

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

Advantages of the Indicator

• Simplicity: clear and easily communicable metric.
• Action-oriented: encourages adoption of conservation agriculture practices.
• Complementary value: adds context to standalone blue and green water footprints.

Limitations

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

The Green-to-Blue Ratio provides a quick and practical guide for assessing and improving water sustainability, helping reduce pressure on blue water sources in vulnerable or water-stressed regions.