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Indicator Assessment
Water exploitation index plus (WEI+) for river basin districts (2002-2014)
Note:
This interactive map allows users to explore changes over time in water abstraction by source and water use by sector at sub-basin or river basin scale. The WEI+ has been calculated as the quarterly average per river basin district, for the years 2002-2014, as defined in the European catchments and rivers network system (ECRINS). The ECRINS delineation of river basin districts differs from that defined by Member States under the Water Framework Directive, particularly for transboundary river basin districts.
The water exploitation index plus (WEI+), which assesses the total freshwater used as a percentage of the total renewable freshwater resources available, is an indicator of the pressure or stress on freshwater resources. A WEI+ of above 20 % implies that a water unit is under stress, while a WEI+ of over 40 % indicates severe stress and clearly unsustainable resource use (Raskin et al., 1997).
Compared with many regions of the world that face serious water shortages, water scarcity in Europe is not considered severe. In general, water is relatively abundant, with, on average, only 5 % of renewable freshwater resources abstracted each year. However, water availability and populations are unevenly distributed. Except for some northern and sparsely populated areas that retain abundant resources, many areas of Europe, particularly the Mediterranean and, to some extent, the densely populated river basins of the Continental region, have high WEI+ values. This is also affected by natural water availability, which is mainly driven by climatic conditions and variability.
In 2014, around 13 river basin districts in the Mediterranean region, including Greece, Portugal and Spain, were facing water stress conditions (WEI+ > 20 %) (see the map in Figure 2 and the Policy context and targets section). In 2014, the highest WEI+ value was estimated for the Spanish and Portuguese islands, followed by the Segura river basin in Spain (WEI+ = 62 %). This makes water resource management in these river basins particularly challenging.
Across Europe, water abstraction from surface resources accounts for 58 % of total water resources, while for groundwater the figure is 42 %. Rivers and groundwater aquifers supply 83 % of the total annual water used in Europe. During summer, water abstraction from rivers, groundwater and lakes increases by, on average, almost 50 % compared with winter, resulting in the lower availability of renewable water resources in summer than in winter.
To reduce the impacts of declining water availability, particularly in the summer months, two major measures have been widely implemented across Europe: more dams and reservoirs have been constructed to store more water for the summer months and, increasingly, more water is being used from groundwater resources. Since the 1950s, the number of reservoirs has increased by more than three times. In recent years, a new way of reducing the impacts of limited water availability has been developed through investments in desalinations plants, mainly in Cyprus, Malta and Spain.
The Mediterranean region stores the largest volume of reservoir water in Europe, namely 38 % of the total volume of reservoir water, while 30 % of reservoir water is stored in the Atlantic region of Europe and 20 % in the Continental region. These infrastructures cause substantial changes to the natural hydrological regimes (hydromorphological pressures and modifications) of rivers.
Water abstraction from groundwater resources is quite stable, accounting for almost 42 % of total water abstractions. The overexploitation of groundwater aquifers can have ecological impacts, such as the lowering of groundwater tables, the drying out of springs and the occurrence of salt-water intrusion. These impacts have already been observed in Europe, particularly in the Mediterranean coastal areas (EEA, 2012b).
Freshwater is the most important resource for humankind, cross-cutting all social, economic and environmental activities. It is necessary for all life on our planet, an enabling or limiting factor for any social or technological development, a possible source of welfare or misery, and a reason for cooperation or conflict (UNESCO, 2013). All economic sectors need water for their activities. Agriculture, industry and most forms of energy production are not serviceable if water is not available.
The WEI+ is driven by two important factors: climate and water demand. The climate controls water availability and seasonal fluctuations in water supply, and water demand is linked to population density and the related economic activities in a given area.
Around 140 km3 of water is abstracted annually to meet the demand for socio-economic activities, such as agriculture, household activities, industry, mining and quarrying, as well as energy production. This corresponds to around 5 % of total renewable freshwater resources. However, not all the water abstracted is consumed. After abstraction, water is used for different purposes. For instance, water used for a shower is returned back to the environment via urban wastewater treatment plants. Around 42 % of water abstracted is later returned back to the environment. In other terms, 58 % of water is consumed for different socio-economic activities in Europe. However, there are regional and seasonal differences in water abstractions.
Water use in agriculture (irrigation), forestry and fishing
The total area of arable land in Europe is around 113 million ha. About 70 % of total arable land is located in France (16 %), Spain (11 %), Germany (10 %), Poland (10 %), Romania (8 %), Italy (7 %) and the United Kingdom (6 %). Slightly more than 30 % of arable land can be irrigated. Depending on the climatic conditions of the particular year, the actual area of irrigation may change from year to year, from 8 to 9 % of the total crop area (Eurostat, 2013a).
Cereals and permanent grasslands are two major crop types and they occupy more than 60 % of the utilised agricultural area. Permanent crops are mainly located in Mediterranean countries, while temporary grasses are mainly found in northern countries.
Despite the fact that a comparatively small portion of total arable land is subject to irrigation (only 8–9 % of the total crop area), on an annual scale, these areas account for about 51 % of total water use in Europe, and this percentage can increase by up to 66 % in the spring. In particular, in the Mediterranean region, water use for irrigation accounts for almost 80 % of total net water use. In many locations in the Mediterranean region, agriculture is the main pressure on freshwater resources during the summer months. Since 2002, the total area of irrigated land in Europe has decreased by around 6 %, while utilised crop areas increased by 4 % in the same period. However, the total area of irrigated land in southern Europe increased by 12 % over the same period, and this is associated with an increase in utilised crop areas.
In 2014, total harvested agricultural production had increased by 22 % in eastern Europe and by 6 % in western Europe since 2002. However, despite a 12 % increase in the irrigated area of southern Europe, harvested agricultural production decreased by 36 % between 2002 and 2014.
As for the regional pattern of changes (percentages) in utilised crop areas and irrigated areas per country, increases have been observed for irrigated areas, particularly in Latvia (528.9 %), followed by Lithuania (186.9 %), Portugal (82.7 %), Austria (31 %), Italy (17.3 %), Germany (4.9 %) and Bulgaria (4.5 %).
According to the predictions made in previous studies, a slight increase in the water requirement for irrigation (EEA, 2014b), associated with a decrease in precipitation in southern Europe (EEA, 2015e), together with the lengthening of the thermal growing season, may be expected in the coming years and this may worsen the water scarcity conditions for agriculture.
Water collection, treatment and supply (public water supply) and service sector
Water collection is the second largest sector (24 %) after agriculture. Growing urban populations and higher living standards, coupled with reduced water availability because of pollution and drought, mean that large cities or dry regions with a high population density are particularly vulnerable to water stress. In the past, Europe’s larger cities have generally relied on the surrounding regions for their water supplies. Many large cities have already developed wide networks for transporting water, often over distances of more than 100–200 km, to be allow them to respond to water demands.
In Europe, about 87 % of the total annual water supplied by the public water supply system is used in the Continental (32 %), Atlantic (28%) and Mediterranean (26 %) regions. These regions are home to more than 453 million people (88 % of the total population of Europe in 2014). The Mediterranean region is the largest consumer of water in total (45 %).
An average European citizen uses 134 m3/year of water from renewable freshwater resources. This corresponds to approximately 370 L of water/capita per day. These figures exclude recycled, reused and desalinated water, as well as water used in other economic sectors covered by self-supply.
The highest estimated water use per capita occurs in the Mediterranean region, with a use level of 707 L/capita per day. This is followed by the Alpine and Continental regions, with use values of 380 and 275 L/capita per day, respectively.
As water abstraction, supply and use for household activities are mainly driven by population, population dynamics, particularly in urban areas, have a significant impact on water abstraction and use for households. The European population has increased by around 117 million (24 %) over the last three decades (1987–2015). During this same period, the urban population has increased by around 120 million. Despite this, water abstraction for local residents decreased by around 3.8 % overall between 2002 and 2012.
Meanwhile, tourism has become a driving force of the increasing pressures on the public water supplies in many locations across Europe. Every year, millions of people temporarily move from their homes to other destinations in Europe. This mobility accounts for around 9 % of the total annual water use, which is attributed to accommodation and food service activities in Europe.
Some of the most popular tourist destinations in Europe are the European capital cities. With destinations such as Paris, London and Brussels, the Atlantic region has the highest proportion of total water use for accommodation and food services in Europe (40 %). This region is followed by the Continental region (28 %), which has a number of historical towns and cities that attract millions of tourists every year.
Tourism, particularly in the Mediterranean islands, has a great impact on water use. The average number of tourists that visit the Mediterranean islands per year is 16 times higher than the permanent local populations of these islands. Because of pressures from tourism on the use of renewable water resources, small Mediterranean islands have a WEI+ that is constantly above 20 % throughout the year.
Between 2002 and 2012, water abstraction for tourists increased by 78 %. Some of this increase can be accounted for by winter tourism, particularly in eastern Europe. Almost five times more water was abstracted in eastern Europe in 2012 than in 2002. Similarly, in western Europe, water abstraction for tourism increased by around 150 %. In contrast with this development in eastern and western Europe, water abstraction for tourism in southern Europe shows a decreasing trend (a 26 % decrease in winter and a 13 % decrease in summer). A decoupling can be observed between the number of tourists and water abstraction levels in southern Europe, although southern Europe still has the highest water abstraction per tourist.
Water is returned back to the environment after use by households. The returned water, which is also known as 'grey water', is discharged back into the environment either treated or untreated. Wastewater treatment plants play a significant role in the reduction of the environmental impacts of water use by households. Wastewater treatment in all parts of Europe has improved over the last 15–20 years. The percentage of the population connected to wastewater treatment facilities in southern, south-eastern and eastern Europe has increased over the last 10 years. However, around 30 million inhabitants are still not connected to wastewater treatment plants in Europe.
Water abstraction for cooling in energy generation purposes
In general, hydropower is regarded as non-consumptive in a water use context. Indeed, water is returned back to the environment after being used in electricity production by hydropower. However, it has to be noted that this process is not impact free on the environment or freshwater ecosystems. Water abstraction for hydropower deteriorates the natural water cycle in rivers and lakes. In 2014, around 14 % of total electricity was generated by hydropower. Electricity production and the proportion of electricity generated from renewable sources is growing rapidly in Europe. In parallel with this trend, the capacity for hydroelectric production increased by 44 % between 1990 and 2014.
Water is also used for cooling. Between the 1990s and 2010s, water use for cooling decreased by around 14 % and 21 % in western and eastern Europe, respectively. On the other hand, water use for cooling in southern Europe increased by 3 %. Although the cooling process leads to a negligible amount of water loss due to evaporation, water abstraction for cooling still is high. Between 1990 and 2014, electricity production by hydropower increased by 39 %. Hydropower is not considered to be consumptive water use and thus water abstraction for hydropower is excluded from water accounting. However, the environmental impacts of dams remain a subject for integrated assessment.
Water is used by different types of power plants, e.g. nuclear power plants, and gas- or solid-fuel-based combustion plants, for cooling purposes during electricity generation. On an annual scale, around 60 000 hm3 of water is abstracted in Europe for the cooling of power plants. The water consumption factor due to the evaporation that takes place during cooling processes varies from power plant to power plant from 0.2 m3/MWh to 129 m3/MWh. In general, about 1.5 % of total abstracted water is consumed via evapotranspiration. However, this can reach up to 100 % depending on the cooling system and fuel type of the individual installation.
The Continental region uses almost 65 % of total water abstraction for electricity, gas, steam and air conditioning supply, followed by the Atlantic (16 %) and Mediterranean (13%) regions.
Water use for mining, quarrying, manufacturing and construction
In 2014, total water use for mining, quarrying, manufacturing and construction accounted for 3 % of total freshwater use in Europe. More specifically, at the regional scale, the Continental region consumed 42 % of that amount, followed by the Mediterranean (20 %) and Atlantic (16 %) biogeographical regions. There are not significant seasonal variations in water use by this sector, as similar volumes of water are abstracted and used in both winter and summer.
Changes in water abstraction
In general, there has been a decrease in water abstraction in Europe for some economic sectors since the 1990s. For instance, the industrial sector has improved its water efficiency leading to a significant decrease (27 %) in water abstraction over this period. Despite a 7 % decrease in water abstraction, agriculture is still the sector with the highest water demand. Water abstraction for electricity has decreased by 11 % since the 1990s, indicating a more or less constant trend since 2000. Slight improvements have been made in water abstraction for public water supply, with a 3 % decrease since the 1990s. There has been a significant decrease in public water supply in the eastern and western parts of Europe, while public water supply has increased in southern Europe, the western Balkans and Turkey. This decrease in eastern and western Europe might be related to improvements in the water supply network. It should be noted that freshwater abstraction across Europe decreased by about 7.4 % between 2002 and 2014. That is a good achievement. However, measures, particularly in southern and eastern countries, have to be implemented to improve the effectiveness of water use and reduce water use per unit.
The WEI+ provides a measure of the total water use as a percentage of the renewable freshwater resources for a given territory and time scale.
The WEI+ is an advanced and geo-referenced implementation of the WEI. It quantifies how much water is monthly or seasonally abstracted and how much water is returned after use to the environment via basins. The difference between water abstraction and return is regarded as water use.
WEI+ values are given as percentages, i.e. water use as a percentage of renewable water resources. Absolute water volumes are presented as millions of cubic meters (million m3 or hm3).
The objective of the EU's 7th EAP to 2020 is to ensure the protection, conservation and enhancement of the EU’s natural capital and to improve resource efficiency. Monitoring the efficiency of water use in different economic sectors at national, regional and local levels is necessary to achieve this. The WEI is part of the set of water indicators published by several international organisations, such as the United Nations Environment Programme (UNEP), the Organisation for Economic Co-operation and Development (OECD), Eurostat and the Mediterranean Blue Plan. There is an international consensus about the use of this indicator for assessing the pressure of the economy on water resources, i.e. water scarcity.
The WEI+ is an advanced version of the WEI, which better addresses regional and seasonal aspects of water scarcity. In addition, it also takes water use (water abstraction minus water returned) into account. The indicator describes how total water use exerts pressure on water resources. It identifies areas (e.g. sub-basins or river basins) that have high abstraction levels on a seasonal scale in relation to the resources available and that are therefore prone to water stress. Changes in WEI+ values allow analyses of how changes in water use affect freshwater resources, i.e. by putting them under pressure or by making them more sustainable.
There are no specific targets directly related to this indicator. However, the Water Framework Directive (2000/60/EC) requires Member States to promote the sustainable use of water resources, based on the long-term protection of available water resources, and to ensure a balance between abstraction and the recharge of groundwater, with the aim of achieving good groundwater status by 2015.
The EU's Seventh Environment Action Programme (7th EAP) aims to ensure that stress on renewable water resources is prevented or significantly reduced by 2020 (EU, 2013). The EU’s Roadmap to a Resource Efficient Europe (EC, 2011) also includes a milestone for 2020, namely that ‘water abstraction should stay below 20 % of available renewable freshwater resources’. European-scale estimations of water scarcity are likely to shadow large local differences and would thus be misleading. Instead, estimations of the proportional area affected by water scarcity conditions (either seasonally or throughout an entire year) may better capture the actual level of water stress on the continental scale.
Regarding WEI+ thresholds, it is important that agreement is reached on how to delineate non-stressed and stressed areas. Raskin et al. (1997) suggested that a WEI value of more than 20 % should be used to indicate water scarcity, whereas a value of more than 40 % would indicate severe water scarcity. These thresholds are commonly used in scientific studies (Alcamo et al., 2000). Smakhtin et al. (2004) suggested that a 60 % withdrawal from the annual total runoff would cause environmental water stress. Similarly, the Food and Agriculture Organization of the United Nations (FAO) applies a value of above 25 % of water abstraction as an indication of water stress and of above 75 % as an indication of serious water scarcity (FAO, 2017). Since no formally agreed thresholds are available for assessing water stress conditions across Europe, in the current assessment, the 20 % WEI+ threshold proposed by Raskin at al. (1997) is considered to distinguish stressed from non-stressed areas, while a value of 40 % is used as the highest threshold for mapping purposes.
The WEI+ is an advanced version of the water exploitation index. It is geo-referenced and developed for use on a seasonal scale. It also takes into account water abstraction (gross) and return (net abstraction) to reflect water use.
In 2011, a technical working group, developed under the Water Framework Directive Common Implementation Strategy, proposed the implementation of a regionalised WEI+. This differed from the previous approach by enabling the WEI+ to depict more seasonal and regional aspects of water stress conditions across Europe (See Conceptual model of WEI+ computation). This proposal was approved by the Water Directors in 2012 as one of the awareness-raising indicators.
The regionalised WEI+ is calculated according to the following formula:
WEI+ = (abstractions - returns)/renewable freshwater resources.
Renewable freshwater resources are calculated as 'ExIn + P - Eta ± ΔS' for natural and semi-natural areas, and as 'outflow + (abstraction - return) ± ΔS' for densely populated areas.
Where:
ExIn = external inflow
P = precipitation
ETa = actual evapotranspiration
ΔS = change in storage (lakes and reservoirs)
outflow = outflow to downstream/sea.
It is assumed that there are no pristine or semi-natural river basin districts or sub-basins in Europe. Therefore, the formula 'outflow + (abstraction - return) - ΔS' is used to estimate renewable water resources.
Climatic data were obtained from the EEA Climatic Database, which was developed based on the ENSEMBLES Observation (E-OBS) Dataset (Haylock et al., 2008). The State of the Environment database was used to validate the aggregation of the E-OBS data to the catchment scale.
Streamflow data have been extracted from the EEA Waterbase — Water Quantity database. This database does not have sufficient spatial and temporal coverage yet. In order to fill the gaps, Joint Research Centre (JRC) LISFLOOD data (Burek et al., 2013) have been integrated into the streamflow data. The streamflow data cover Europe, in a homogeneous way, for the years 1990-2015 on a monthly scale.
Once the data series are complete, the flow linearisation calculation is implemented, followed by a water asset accounts calculation, which is done in order to fill the data for the parameters requested for the estimation of renewable water resources. The computations are implemented at different scales independently, from sub-basin scale to river basin district scale.
Overall, annually reported data are available for water abstraction by source (surface water and groundwater) and water abstraction by sector with temporal and spatial gaps. Gap-filling methods are applied to obtained harmonised time series.
No data are available at the European scale on 'Return'. Urban waste water treatment plant data, the European Pollutant Release and Transfer Register (E-PRTR) database, Eurostat population data, JRC data on the crop coefficient of water consumption, satellite observed phenology data have been used as proxy to quantify the water demand and water use by different economic sectors. Eurostat tourism data (Eurostat, 2013) and data on industry in production have been used to estimate the actual water abstraction and return on a monthly scale. Where available, state of the environment and Eurostat data on water availability and water use have also been used at aggregated scales for further validation purposes.
Once water asset accounts are implemented according to the United Nations System of Environmental Accounting Framework for Water (2012), the necessary parameters for calculating water use and renewable freshwater water resources are harvested.
Following this, bar and pie charts are produced, together with static and dynamic maps.
For each parameter of water abstraction, return and renewable freshwater resources, primarily data from the Waterbase — Water Quantity database have been used. Eurostat, OECD and Aquastat (FAO) databases have also been used to fill the gaps in the data sets. Furthermore, the statistical office websites of all European countries have each been visited not only once but several times to get the most up-to-date data from these national open sources. Despite this, some gaps still needed to be filled by applying certain statistical or geospatial methodologies (See reference data sources for gap filling and modulation coefficients).
LISFLOOD data from the JRC have been used to gap fill the streamflow data set (See reference data sources for gap filling and modulation coefficients). The spatial reference data for the WEI+ are the European Catchments and Rivers Network System (Ecrins) data (250-m vector resolution). Ecrins is a vector spatial data set, while LISFLOOD data are in 5-km raster format. In order to fill the gaps in the streamflow data, centroids of the LISFLOOD raster have been identified as fictitious (virtual) stations. The topological definition of the drainage network in Ecrins has been used to match the most relevant and nearest fictitious LISFLOOD stations with EEA-Eionet stations and the Ecrins river network. After this, the locations of stations between Eionet and LISFLOOD stations were compared and overlapping stations were selected for gap filling. For the remaining stations, the following criteria were adhered to: fictitious stations had to be located within the same catchment as the Eionet station and have the same main river segment; in addition, both stations had to show a strong correlation.
A substantial amount of gap filling has been performed in the data on water abstraction for irrigation. First, a mean factor between utilised agricultural areas and irrigated areas has been used to fill the gaps in the data on irrigated areas. Then, a multiannual mean factor of water density (m3/ha) in irrigated areas per country has been used to fill the gaps in the data on water abstraction for irrigation.
The gaps in the data on water abstraction for manufacturing and construction have been filled by using Eurostat data on production in industry (Eurostat [sts_inpr_a]) and the E-PRTR database with the methodologies in the best available techniques reference document (BREF) to convert the production level into the volume of water.
Reported data on water abstraction and water use do not have sufficient spatial or temporal coverage. Therefore, estimates based on country coefficients are required to assess water use. First, water abstraction values are calculated and, second, these values are compared with the production level in industry and in relation to tourist movements in order to approximate actual water use for a given time resolution. This approach cannot be used to assess the variations (i.e. the resource efficiency) in water use within the time series.
Spatial data on lakes and reservoirs are incomplete. On the other hand, as reference volumes for reservoirs, lakes and groundwater aquifers are not available, the water balance can be quantified as only a relative change, and not the actual volume of water. This masks the actual volume of water stored in, and abstracted from, reservoirs. Thus, the impact of the residence time, between water storage and use, in reservoirs is unknown.
The sectoral use of water does not always reflect the relative importance of the sectors to the economy of a given country. It is, rather, an indicator that describes which sectors environmental measures should focus on in order to enhance the protection of the environment. A number of iterative computations based on identified proxies are applied to different data sets, i.e. urban waste water treatment plant data, E-PRTR data, Eurostat population data, JRC data on the crop coefficient of water consumption and satellite-observed phenology data have been used as proxies to quantify the water demand and water use by different economic sectors. This creates a high level of uncertainty in the quantification of water return from the economic sectors, thus also leads to uncertainty with regard to the 'water use' component.
In order to distribute population data across Europe, the Geostat 2011 grid data set from Eurostat was used. Then, further aggregations were performed in the spatial dimension to give the sub-basin and functional river basin district scales of Ecrins spatial reference data. The population within the time frame of one calendar year is regarded as stable. Variations are taken into account only for the annual scale. Deviations from officially reported data are expected because of the nature of the methodological steps followed.
The tourist data used were provided by Eurostat and relate to the nights spent per NUTS2 region, on the monthly scale, in accommodation establishments. Because of the aggregation/disaggregation steps followed, deviations from officially reported data are expected. The tourist population was included in the calculation as additional to the stable (local resident) population.
Where monthly data were not available, Eurostat tourist data (Eurostat, 2013), data on industry in production (Eurostat [sts_inpr_a]) and JRC satellite-observed phenology data were used to estimate the actual water abstraction and return on a monthly scale.
A validation of the results has been performed by comparing the estimates with reported data where feasible. Some contradictory results have been observed. For instance, the desalination of sea water is one of the methods used to meet the water demands of Cyprus, Malta and Spain. Based on this use of desalinated water, the actual WEI would be around 35-40 % for Malta. However, as desalinated water is not included in the computation of renewable freshwater resources, the WEI+ for Malta is around 100 %. Similarly, because of some technical issues with the reported data on streamflow, the WEI+ could not be computed for Cyprus. Therefore, the results for Cyprus were excluded from the overall assessment. The average WEI reported for Cyprus is 73.1 % for the years 2009-2013 under Water Framework Directive river basin management plan reporting.
A high degree of inconsistency between sub-basin and functional river basin district scales has been observed for the Guadiana river basin. The estimated WEI+ for Guadiana is 131 % for summer 2015, whereas the estimated WEI+ values for its sub-basins for the same period are as follows: 75 % for Upper Zancara, 41 % for Zujar and 48 % for Ardilla. This inconsistency seems to be related to the computations for the aggregation from sub-basin to functional river basin district for this basin. The value will be corrected once this technical problem has been solved.
Data are very sparse on some particular parameters of the WEI+. For instance, current streamflow data reported by the EEA member countries to the WISE SoE — Water Quantity database do not have sufficient temporal or spatial coverage to provide a strong enough basis for estimating renewable water resources for all of Europe. Such data are not available elsewhere at the European level either. Therefore, JRC LISFLOOD data are used intesively as surrogates (see availability on streamflow data).
Data on water abstraction by economic sectors have better spatial and temporal coverage. However, the representativeness of data for some sectors is also poor, such as the data on water abstraction for mining. In addition to the WISE SoE — Water Quantity database, intensive efforts to compile data from open data sources such as Eurostat, OECD, Aquastat (FAO) and national statistical offices have also been made (see share of surrogate data vs reported data on water abstraction).
Quantifying water exchanges between the environment and the economy is, conceptually, very complex. A complete quantification of the water flows from the environment to the economy and, at a later stage, back to the environment, requires detailed data collection and processing, which have not been done at the European level. Thus, reported data have to be used in combination with modelling to obtain data that can be used to quantify such water exchanges, with the purpose of developing a good approximation of 'ground truth'. However, the most challenging issue is related to water abstraction and water use data, as the water flow within the economy is quite difficult to monitor and assess given the current lack of data availability. Therefore, several interpolation, aggregation or disaggregation procedures have to be implemented at finer scales, with both reported and modelled data. Main consequences of data set uncertainty are the followings;
The Danube river basin is accounted for as a single district in Ecrins, so it aggregates a lot of regional and national information.
The water accounts and WEI+ results have been implemented in the EEA member and Western Balkan countries. However, regional data availability was an issue for some river basins (e.g. in Cyprus, the Jarft in Poland, North West and North Eastern river basins in the United Kingdom, the Kymijoki river basin in the Gulf of Finland, Gran Canarias of Spain and some Icelandic and Turkish river basins), which had to be removed from the assessment.
Because of the aggregation procedure used, slight differences exist between sub-basin and river basin district scales for total renewable water resources and water use.
For references, please go to https://www.eea.europa.eu/data-and-maps/indicators/use-of-freshwater-resources-2/assessment-2 or scan the QR code.
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