Water exploitation index (WEI) — in late 1980s/early 1990s (WEI‑90) compared to latest years available (1998 to 2007)

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.