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Box 4.3 The importance of scaling and decoupling in the estimation of water exploitation and water stress

The spatial scale of analysis is essential in the accurate representation of water scarcity conditions. Highly aggregated scales like country level fail to depict the full problem as deficits between water resources availability and demand in one area can be leveraged by surpluses in other areas. Similarly, separating between surface and groundwater resources can further support the assessment of water exploitation. Cases where one of the resources (e.g. groundwater) is overexploited may not appear when availability and abstractions are calculated as sums.

The Greek case of the RDB of Eastern Sterea Ellada (GR07) is a nice illustrative example. The Water Exploitation Index (WEI) calculated based on the long term average availability places Greece as a non-stressed country with a WEI of 13%. Yet, the RBD of Eastern Sterea Ellada has a much higher WEI of 31%, with its groundwater being overall more exploited than surface water (Map 4.2a). A further analysis conducted at River Basin scale and sub-catchment scale, decoupling also surface water (WEI_SW) and groundwater (WEI_GW) exploitation (Map 4.2b) shows great variability within the RBD, with some basins and catchments being overexploited while others are not-stressed and reveals a large range of exploitation rates of the surface and groundwater. This scale of analysis can better support the identification of the problem (together with additional management indicators) and guide targeted actions.

Map 4.2a The WEI for the Greek River Basin District Eastern Sterea Ellada (GR07).

Source: Compiled by the ETC/ICM based on data provided in the Drought and Water Scarcity Management Plan of GR07 (Hellenic Ministry of Environment, Energy and Climate Change and NAMA S.A 2012).
Note: WEI total (31%) and calculated for surface (21%) and groundwater resources (36%) separately, legend: see Map 4.2b, all values in class 20-40%

Map 4.2b The WEI at river basin and subcatchment scale within the Greek RBD Eastern Sterea Ellada (GR07).

Source: Compiled by the ETC/ICM based on data provided in the Drought and Water Scarcity Management Plan of GR07 (Hellenic Ministry of Environment, Energy and Climate Change and NAMA S.A 2012).
Note: WEI total (left), for surface (middle) and groundwater resources (right) at river basin (top) and subcatchment scale (bottom) within the Greek RBD Eastern Sterea Ellada (GR07).

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