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The warning threshold, which distinguishes a non-stressed from a water scarce region, is around 20 %, with severe scarcity occurring where the WEI exceeds 40 %.
WEI (water exploitation index) divides the total water abstraction by the long-term annual average resource. However, this indicator does not fully reflect the level of stress upon local water resources: this is primarily because the WEI is based on annual data and cannot, therefore, account for seasonal variations in water availability and abstraction.