Blue Water Scarcity

Blue water scarcity is an indicator that compares the consumption of surface and groundwater resources (blue water footprint) with the availability of renewable freshwater within a river basin over a specific period. It helps determine whether current water withdrawals are sustainable or if they compromise environmental flow requirements.

Typical Formula

Blue Water Scarcity = Blue Water Footprint / (Blue Water Availability − Environmental Flow)

A value greater than 1 indicates that demand exceeds the sustainable supply.

Importance of the Indicator

• Basin planning: identifies critical areas and prioritizes investment in water management.
• Water footprint assessment: complements traditional accounting by adding a sustainability dimension.
• Corporate risk management: helps companies assess the vulnerability of suppliers and operations to water shortages.

Data Requirements

• Annual blue water footprint by sector (agriculture, industry, domestic use).
• Minimum environmental flows needed to sustain ecosystems.
• Renewable water availability: average flow minus downstream return flows.

Calculation Tools

• Water Footprint Assessment (WFN).
• Aqueduct Water Risk Atlas (WRI).
• AWARE+ (Available WAter REmaining): indicator for spatially explicit water scarcity.

Reduction Strategies

• Agricultural efficiency: improve irrigation and shift away from high-consumption crops.
• Aquifer recharge: implement managed groundwater replenishment techniques.
• Water reuse and advanced treatment: promote circular use of water in industrial and urban systems.

Relationship with Other Indicators

• Water stress: measures total withdrawals relative to availability but may not account for environmental flows or actual consumption.
• Green-to-Blue Ratio (G/B): encourages substituting blue water (irrigation) with green water (rainfall).

Blue water scarcity provides a quantitative framework to evaluate the sustainability of freshwater use within a basin and to guide responsible allocation policies that balance human needs and ecological integrity.