The Water Exploitation Index plus (WEI+) has been calculated as the quarterly average per country for the years 2000–2023. The WEI+ - referred to as the seasonal water scarcity - expresses total water consumption as a percentage of the renewable freshwater resources available in European countries. Each season corresponds to a calendar quarter: Q1 (January–March), Q2 (April–June), Q3 (July–September) and Q4 (October–December).

The WEI+ values presented may differ from nationally available figures, particularly for countries where data availability is limited in the WISE SoE – Water Quantity database (WISE 3) or in the Eurostat water database.

Water abstraction data were taken from WISE 3 (Waterbase - Water Quantity: https://www.eea.europa.eu/en/datahub/datahubitem-view/a4324714-784a-4763-b8b9-b8939ead87fe) and the Eurostat water database (Water statistics on national level (env_nwat): https://ec.europa.eu/eurostat/cache/metadata/en/env_nwat_esms.htm), although the time series contain significant gaps. To address this, extensive gap-filling was applied, and proxies were used to disaggregate annual data to quarterly.

Due to the limited availability of data on water use and return flows in WISE 3 (Waterbase - Water Quantity: https://www.eea.europa.eu/en/datahub/datahubitem-view/a4324714-784a-4763-b8b9-b8939ead87fe), return flows were estimated using sector-specific coefficients calculated from UWWTP capacities (Waterbase - UWWTD: Treatment Plants: https://www.eea.europa.eu/en/datahub/datahubitem-view/6ffd0af1-64eb-4cce-9970-0028e01ee64e), and the Eurostat population change dataset (Population (national level) (demo_pop): https://ec.europa.eu/eurostat/cache/metadata/en/demo_pop_esms.htm), among others.

The EEA calculates the Water Exploitation Index plus (WEI+) for Europe using a consistent approach for Renewable Water Resources (RWR). Data on precipitation, actual evapotranspiration, and outflow were obtained from WISE 3 (Waterbase - Water Quantity: https://www.eea.europa.eu/en/datahub/datahubitem-view/a4324714-784a-4763-b8b9-b8939ead87fe) and the Eurostat water database (([env_wat_res]): https://ec.europa.eu/eurostat/databrowser/view/env_wat_res/default/table?lang=en&category=env.env_wat.env_nwat) Renewable freshwater resources). Reservoir water balance data are available in WISE 3 (Waterbase - Water Quantity: https://www.eea.europa.eu/en/datahub/datahubitem-view/a4324714-784a-4763-b8b9-b8939ead87fe), but coverage across EIONET member countries is spatially and temporally incomplete. Copernicus CEMS EFAS ( https://10.0.95.61/cds.e3458969) and Copernicus Land ERA5 ( https://doi.org/10.24381/cds.68d2bb30) data have been used for gap filling in outflow and reservoir water balance, which may result in differences from national estimates.

The WEI+ for Switzerland and France may involve high uncertainties due to the use of modelled data as the baseline for the computation.

Italy has noted that, due to the approach used by EEA for RWR, the pan-European index does not accurately reflect the detailed water stress conditions in its river basins.

The WEI+ values for the following basins from Norway (i.e., NO1107, NO1108, NO1109, NO5107, and NO5109) represent the state of 2022 due to the lack of computed results for 2023.

The joint field in the spatial data is thematicId, and in the dataset wei_2000_2023_SDI_RiverBasinScale, the corresponding field is also spatialUnitIdentifier.