Physical water scarcity metrics for monitoring progress towards SDG target 6.4: An evaluation of indicator 6.4.2 "Level of water stress".

Target 6.4 of the recently adopted Sustainable Development Goals (SDGs) deals with the reduction of water scarcity. To monitor progress towards this target, two indicators are used: Indicator 6.4.1 measuring water use efficiency and 6.4.2 measuring the level of water stress (WS). This paper aims to identify whether the currently proposed indicator 6.4.2 considers the different elements that need to be accounted for in a WS indicator. WS indicators compare water use with water availability. We identify seven essential elements: 1) both gross and net water abstraction (or withdrawal) provide important information to understand WS; 2) WS indicators need to incorporate environmental flow requirements (EFR); 3) temporal and 4) spatial disaggregation is required in a WS assessment; 5) both renewable surface water and groundwater resources, including their interaction, need to be accounted for as renewable water availability; 6) alternative available water resources need to be accounted for as well, like fossil groundwater and desalinated water; 7) WS indicators need to account for water storage in reservoirs, water recycling and managed aquifer recharge. Indicator 6.4.2 considers many of these elements, but there is need for improvement. It is recommended that WS is measured based on net abstraction as well, in addition to currently only measuring WS based on gross abstraction. It does incorporate EFR. Temporal and spatial disaggregation is indeed defined as a goal in more advanced monitoring levels, in which it is also called for a differentiation between surface and groundwater resources. However, regarding element 6 and 7 there are some shortcomings for which we provide recommendations. In addition, indicator 6.4.2 is only one indicator, which monitors blue WS, but does not give information on green or green-blue water scarcity or on water quality. Within the SDG indicator framework, some of these topics are covered with other indicators.

Erratum: Human pressures and ecological status of European rivers.

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Human pressures and ecological status of European rivers.

Humans have increased the discharge of pollution, altered water flow regime and modified the morphology of rivers. All these actions have resulted in multiple pressures on freshwater ecosystems, undermining their biodiversity and ecological functioning. The European Union has adopted an ambitious water policy to reduce pressures and achieve a good ecological status for all water bodies. However, assessing multiple pressures on aquatic ecosystems and understanding their combined impact on the ecological status is challenging, especially at the large scale, though crucial to the planning of effective policies. Here, for the first time, we quantify multiple human pressures and their relationship with the ecological status for all European rivers. We considered ecological data collected across Europe and pressures assessed by pan-European models, including pollution, hydrological and hydromorphological alterations. We estimated that in one third of EU's territory rivers are in good ecological status. We found that better ecological status is associated with the presence of natural areas in floodplains, while urbanisation and nutrient pollution are important predictors of ecological degradation. We explored scenarios of improvement of rivers ecological status for Europe. Our results strengthen the need to halt urban land take, curb nitrogen pollution and maintain and restore nature along rivers.

Intercalibrating classifications of ecological status: Europe's quest for common management objectives for aquatic ecosystems.

Halting and reversing the deterioration of aquatic ecosystems requires concerted action across state boundaries and administrative barriers. However, the achievement of common management objectives is jeopardised by different national quality targets and ambitions. The European Water Framework Directive requires that quality classifications are harmonised via an intercalibration exercise, ensuring a consistent level of ambition in the protection and restoration of surface water bodies across the Member States of the European Union. We outline the key principles of the intercalibration methodology, review the achievements of intercalibration and discuss its benefits and drawbacks. Less than half of the required intercalibration has been completed, mostly due to a lack of national assessment methods. The process has fostered a scientific debate on ecological classification with important implications for environmental management. Despite a significant level of statistical abstraction, intercalibration yielded a fundamental and unified vision of what constitutes good ecology across Europe, in principle ensuring greater parity in the funds invested to achieve good ecological status.

Towards good ecological status of surface waters in Europe--interpretation and harmonisation of the concept.

The Water Framework Directive (WFD) is a new legislative framework to manage, use, protect, and restore surface water and groundwater resources and coastal waters in the European Union (EU). The aim is to ensure sustainable water management and to reach good water quality by 2015. The assessment of the ecological status and setting of the practical management goals require several steps. The process has started with the characterisation of the river basins including identification of surface water bodies and types, and identification of significant anthropogenic pressures and impacts. The water bodies will be classified in five quality classes (high, good, moderate, poor, bad) based on the Ecological Quality Ratio, which is a ratio between reference conditions and measured status of the biological quality elements. The normative criteria for high, good and moderate ecological status described in the WFD need to be made operational because those will be used to set the practical quality targets for surface water management. National ecological assessment systems and classifications will be harmonised through the WFD intercalibration exercise in order to ensure an equal level of ambition in achieving good surface waters status all over Europe.