Water Vulnerability

Water vulnerability measures the degree to which a system (basin, community, company, or ecosystem) is susceptible to harm from variability and changes in water availability, quality, and accessibility. It combines exposure, sensitivity, and adaptive capacity, and is used to prioritise climate-adaptation investments.

Key Components

• Exposure → Average water deficit (mm) · Weight: 0.35
• Sensitivity → Agricultural GDP / Total GDP and % rural population · Weight: 0.35
• Adaptive capacity → Per-capita income and drinking-water coverage · Weight: 0.30

Water Vulnerability Index (WVI)

WVI = Σ (Normalised indicator × weight)
(Scale 0 = very low · 1 = very high)

Example – Segura Basin (2023)

• Exposure: 0.74 × 0.35 = 0.26
• Sensitivity: 0.65 × 0.35 = 0.23
• Adaptive capacity: 0.40 × 0.30 = 0.12

WVI = 0.61 → High vulnerability

Determinant Factors

• Semi-arid climate and high interannual precipitation variability (CV > 25%).
• Economic structure dependent on intensive irrigated agriculture.
• Undersized infrastructure: network losses above 20%.
• Institutional framework: delays in the approval of river-basin plans.

Direct Consequences

• Potential 30% reduction in agricultural production during extreme droughts.
• 18% increase in urban water costs due to desalination and transfers.
• Social conflicts over resource allocation and maintenance of environmental flows.

Reduction Strategies

• Reuse (200 hm³/year) → Reduces WVI by 0.07 · Time horizon: 5 years.
• Renewable-powered desalination → Reduces WVI by 0.05 · Horizon: 7 years.
• Agricultural climate insurance → Reduces WVI by 0.03 · Horizon: 3 years.
• Irrigation modernisation → Reduces WVI by 0.06 · Horizon: 4 years.

Relation to Other Concepts

• Water deficit: main component of exposure.
• Water security: the inverse objective; increasing security reduces vulnerability.
• Water adaptation: action plan to reduce vulnerability.

A higher level of water vulnerability makes it more urgent to invest in water savings, diversification of sources, and institutional strengthening. A WVI above 0.6 is associated with a critical risk of water crisis before 2030.