4. Pressures, state and outlook

General comments on chapter 4

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4.     Pressures, state and outlook

4.1.    Introduction

As highlighted in the previous Chapter, the added emphasis on ecosystem services represents a move away from perceiving water management within the traditional sectoral responsibilities of fulfilling an ever increasing human water demand and  providing adequate flood defences.  It is also clear that a good understanding of the spatial and temporal variability of water resources is an essential part of evidence based environmental policy making. The acknowledgement of variability as an inherit part of the water resources system necessitates the introduction of a more risk-based management framework, where concepts such as resilience and vulnerability should form the basis of future indicators rather than fixed target figures for water demand and flood defence levels. 

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This already complex task is then further exacerbated by the predicted impacts of change on the water cycle; through climate change and more direct interventions such as land-use management and urbanisations. Also, many cause and effect relationships between the hydrological and the socio-economic systems, and between hydrology and ecosystems, are not currently well-understood. Thus, there are considerable challenges in identifying notionally optimal strategies for effective water resources management.  For operational purposes vulnerability and resilience are linked to incidents where a system state (e.g. flow, ground water level, pollution concentration, etc.) enters a domain that is considered unsatisfactory (or even bad); for example, too much (flood), too little (drought) or too dirty (water quality).

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Given the close link between water and ecosystems combined, and with the added emphasis on resilience and vulnerability, it is essential to develop a good understanding of the water resources systems that are characterised by natural variability and, in particular, the water demand as well as the magnitude and frequency of extreme events (see also (EEA (report under preparation) 2012b), section 3.3). Of special concern is the impact of environmental change (climate change, land-use management, and urbanisation) on these aspects of the hydrological cycle and how they might affect social and environmental systems.

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The purpose of this section is to review current states and trends of Europe’s water resources and to identify external drivers of change with relevance for water resources management and the resulting pressure exerted on Europe’s water resources. This will be followed by a review of the possible projections of future state of Europe’s water resources. Effective management of water resources is required to ensure that throughout Europe a sufficient quantity of good quality water is available for people’s needs and for the environment, as well as ensuring adequate protection against the adverse impacts caused by floods. The temporal and spatial scales characterising the hydrological system vary considerably across Europe. For example, a local flash flood can happen in a manner of hours, while regional water scarcity can develop over years and even decades.

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4.1.1.      An introduction to floods and drought in a European context

Before discussing the main pressures acting on Europe’s water resources and the resulting impacts, a brief overview is given of the current situation with regards to water scarcity and droughts, and to flooding. First, the Water Exploitation Index (WEI) will be introduced, which is used for mapping the balance between water availability and demand across Europe. Next, a discussion of trends in flood occurrence will highlight the current lack of a coherent European program for collecting data and information on past floods.

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The current state of Europe’s water resources is perceived to be under increasing pressure from a range of external drivers primarily driven by increased population and associated resource requirements, climate change (Weiß and Alcamo 2011) and land-use changes (Metzger et al. 2006). These drivers will translate into physical pressures on the water resources systems through changes in both the climatological and terrestrial components of the hydrological cycle and their interactions.

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Changes in the climate component of the water cycle ([1])

Temperature and precipitation are two key climate variables (EEA (report under preparation) 2012b, section 2.2). Time series show long-term warming trends of European average annual temperature since the end of the 19th century, with most rapid increases in recent decades. The last decade (2002-2011) was the warmest on record globally and in Europe. Heat waves have also increased in frequency and length. All these changes are projected to continue at an increased pace throughout the 21st century. Precipitation changes across Europe show more spatial and temporal variability than temperature. Annual precipitation trends since 1950 show an increase by up to 70 mm per decade in North-eastern and North-western Europe – most notably in winter - and a decrease by up to 70 mm in some parts of southern Europe. In Western Europe intense precipitation events have provided a significant contribution to the increase. Most climate model projections show a continued precipitation increases in northern Europe (most notably during winter) and decreases in southern Europe (most notably during summer). The number of days with high precipitation is projected to increase.

[1] This section is based on EEA (report under preparation), 2012b, where the reader is referred to for more detailed information and primary sources

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Besides the trends in average values, also the extremes of temperature and precipitation are of importance for water scarcity and droughts and floods. Extremes of cold have become less frequent in Europe while warm extremes have become more frequent. Since 1880, the average length of summer heat waves over Western Europe has doubled and the frequency of hot days has almost tripled. Extreme high temperatures are projected to become more frequent and last longer across Europe over the 21st century. There are no widespread significant trends in either the number of consecutive dry or wet days across Europe. Heavy precipitation events are likely to become more frequent in most parts of Europe. The changes are strongest in Scandinavia in winter and in northern and eastern central Europe in summer.

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Observed changes in temperature and precipitation have already been found to affect river flow, with substantial regional and seasonal variation across Europe (EEA (report under preparation) 2012b, section 3.3). In general, flows have increased in winter and decreased in summer since the 1960s. Climate change is projected to result in strong changes in the seasonality of river flows across Europe. Summer flows are projected to decrease in most of Europe, including in regions where annual flows are projected to increase.

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Severity and frequency of droughts appears to have increased in parts of Europe. The impact of river flow droughts is currently largest in Southern and South-Eastern Europe. These impacts will further increase with prolonged and more extreme droughts. Minimum river flows will not only decrease in Southern and South-Eastern Europe but also decrease significantly in many other parts of the continent, especially in summer.

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The rise in the reported number of flood events over recent decades results mainly from better reporting and from land-use changes. The effect of climate change is projected to intensify the hydrological cycle and increase the occurrence and frequency of flood events in large parts of Europe. However, estimates of changes in flood frequency and magnitude remain highly uncertain. In regions with reduced in snow accumulation during winter, the risk of early spring flooding would decrease.

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Changes in the terrestrial component of the water cycle

Most European countries expect a continuation of current land-use specialisation trends: urbanisation, agricultural intensification and abandonment, and natural afforestation (EEA 2010e). This happens in the context of an overall slow-down of total land changes observed in 2000–2006 and the substitution of residential area expansion with dominant growth of economic sites (EEA 2010e). Figure 4.1 shows the predominate net land conversion in Europe.

Figure 4.1 Predominant net land conversions in Europe 1990-2006

Source: EEA, 2010e
Note: based on Corine Land Cover Analysis

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The total area of land use change from agriculture to artificial surfaces between 2000 and 2006 varies across Europe. At country level the highest share of land use change from agriculture to artificial area occurred in the EU-27 is in Cyprus (1.7 %), the lowest in Malta (0.0%) (Figure 4.2). In general the highest percentage of agricultural land (in 2000) converted to artificial surfaces (by 2006) occurred in urban regions. The sector share of land converted from agriculture to artificial surfaces indicates which sectors take up most agricultural land. Most of the agricultural land in Europe is taken by the housing sector (38 %), followed by construction sites (28%) and the industrial and commercial sector (18%) (EEA 2012a) (Figure 4.3).

Figure 4.2 Change in land use from agriculture to artificial surfaces as a percentage of agricultural area (in 2000)

Source: EEA 2012a
Note: for administrative regions NUTS 0, 2 and 3

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Figure 4.3 Sector share of land converted from agriculture to artificial surfaces (%)

Source: (EEA 2012a)

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Conversion of agricultural land to artificial surfaces, which is also known as soil sealing can have several environmental impact on soil, water and biodiversity resources. The sealing may increase the risks of soil erosion and water pollution. It also disturbs agricultural habitats, impact on animal migration patterns and affects the hydrological cycle (increased water runoff and decreased water retention) leading to an increased risk of floods.

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But we have to avoid making urbanisation similar to increased flooding and agriculture ideal for water resource management. There’s a menu of possibilities for managing flood risks in urban areas, on catchment scale, neighbourhood scale and for individual buildings (Shaw, Colley, and Connell 2007; EEA 2012c). Intensive agricultural practices can influence hydro-morphology of rivers, and lead to increased water use and pollution of groundwater when fertilisers and pesticides wash out if water is not used efficient (EEA 2012b).

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4.2.    Water scarcity & droughts

4.2.1.      Water accounts and water exploitation index

Over the past thirty years, drought events and the number of areas and people affected have dramatically increased both in number and intensity within the EU (Mediterranean Water Scarcity & Drought Working Group (MED WS&D WG) 2007). Severe events have been identified that on annual basis affected more than 800 000 km² of the EU territory (37%) and 100 million inhabitants (20%) in 1989, 1990, 1991 and more recently in 2003 (with an exceptional cost of 8.7 billion €, EC 2007a) and in 2007-2008.

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During 2011, in the period January to May, severe cumulated rain deficits were recorded in the EU , comparable to historic minima for many countries (Figure 4.4): in France (comparable to 1976), England (comparable to 1997), Belgium, The Netherlands (comparable to 1991, 1982, 1976), Germany (comparable to 1996), Denmark, parts of Czech Republic and Slovakia, almost all of Hungary, locally in Austria, Slovenia and Croatia, Ukraine (absolute minimum since 1975), Belarus and the Baltic countries (JRC 2011). The evolution of the 3-month Standardized Precipitation Index (SPI3) from February to May 2011 is in figure 4.5.

Figure 4.4 Accumulated rainfall for 1st of January to 6th of June 2011

Source: JRC (2011)
Note: Comparison of accumulated rainfall for 1st of January to 6th of June 2011 with the historic time series 1975 to 2010.2011 is highlighted in red. Black dot-dashed line: Average rainfall 1975-2010, green dashed lines: One standard deviation above and below the average (1975-2010).

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Figure 4.5 Evolution of the 3-month Standardized Precipitation Index (SPI3) from February to May 2011

Source: JRC (2011)
Note: Values below -1.5 indicate a severe meteorological drought. Grey shading indicates areas with insufficient reliable data to compute the SPI

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In 2012, reduced rainfall, below normal levels, has been recorded during the winter months, impacting the water resources of extended parts of Southern and Central Europe (JRC 2012). Based on the Standard Precipitation Index (SPI1) for February2012, France, Spain, Portugal and England experienced extreme and severe drought condition, even more pronounced in the low cumulative rainfall as expressed by the SPI3 (December-January-February). Based on the daily soil moisture anomaly indicator the drought impacted Spain, Portugal, Southern France, Central Italy, Greece (locally), Hungary, Bulgaria and Romania, with affected areas were also evident in Denmark, North Italy (Po river) and Northern UK (JRC 2012). Figure 4.6 below presents snapshots of drought condition in Europe as calculated by the European Drought Observatory (EDO) using the Combined Drought Indicator, based on SPI, soil moisture and fAPAR.

Figure 4.6 Mapping of drought conditions in Europe

Source: European Drought Observatory (EDO), Joint Research Centre, European Commission
Available online: http://edo.jrc.ec.europa.eu/edov2/php/index.php?id=1146
Note: Mapping of drought conditions in Europe as calculated by the Combined Drought Indicator (based on SPI, soil moisture and fAPAR) for top left March 21st, 2012 top right May 21st, 2012 and bottom left May 1st, 2003 known as a dry year for large parts of Europe.
There are three classification levels: watch (when a relevant precipitation shortage is observed), warning (when the precipitation translates into a soil moisture anomaly), alert (when these two conditions are accompanied by an anomaly in the vegetation condition)

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Note: A map or table to illustrate the statements above will be included in the final version based on the reactions of member states on the questionnaire on data, more specific the “Historic Drought events in Europe”.

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Action required during Eionet consultation

The WEI+ maps are in map 4.1a and map 4.1b based on latest available year and ltaa respectively. We also refer to maps in a separate document (add link to document on forum) with yearly WEI maps from 2002 until 2006 on RBD and Country level.

Latest available year is comparable to the definition as used for the WEI+, ltaa is continuation of methodology of previous WEI and less dependent of yearly variations in water availability.

  1. We also refer to the questions (add link to document on forum) about the reported values and strongly suggest to have a detailed look at the data for your country and add or correct asap.
  2. Based on the comments, a final WEI+ map will be included in the EEA report on Vulnerability, followed by an interpretation of the map

Also information on “Historic Drought events in Europe” is requested in this questionnaire.

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The Water Exploitation Index WEI (defined as the ratio of annual abstraction over long term annual availability (ltaa), see Box 4.1) is used to quantify the pressure (stress) exerted on the environment (i.e. the natural water resources) by anthropogenic activities (i.e. water abstraction).

Map 4.1a Water Exploitation Index WEI and abstraction for European River Basin Districts (latest available year)

Sources: compiled by the ETC/ICM
Notes: Data come from multiple sources, Combination of WISE-SoE#3 and WFD: AT2000-Rhine, AT5000-Elbe, BG1000-Danube Region, BG2000-Black Sea Basin, BG3000-East Aegean, BG4000-West Aegean, SK30000-Vistula, SK40000-Danube / Combination of WISE-SoE#3 and websources: IEGBNISH-Shannon / Websources: ES014-Galician Coast, ES016-Cantabrian, ES020-Duero, ES030-Tagus, ES040-Guardiana, ES050-Guadalquivir, ES07-Segura, ES080-Jucar,ES091-Ebro, ES100-Internal Basins of Catalonia, ES110- Balearic Islands, ES120-Gran Canaria. web link: http://servicios2.marm.es/sia/visualizacion/lda/recursos/superficiales_escorrentia.jsp (*Total water resources in the natural system (hm3/year) Average value for the period between 1941-2009) Reported to DG ENV for the Interim Report: PTRH3, PTRH4, PTRH5, PTRH6, PTRH7, PTRH8 WISE-SoE#3: all other RBDs / Eurostat JQ IWA: all Country level data to be checked on completeness and correctness

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Map 4.1b Water Exploitation Index WEI and abstraction for European River Basin Districts (ltaa)

Sources: compiled by the ETC/ICM
Notes: Data come from multiple sources, Combination of WISE-SoE#3 and WFD: AT2000-Rhine, AT5000-Elbe, BG1000-Danube Region, BG2000-Black Sea Basin, BG3000-East Aegean, BG4000-West Aegean, SK30000-Vistula, SK40000-Danube / Combination of WISE-SoE#3 and websources: IEGBNISH-Shannon / Websources: ES014-Galician Coast, ES016-Cantabrian, ES020-Duero, ES030-Tagus, ES040-Guardiana, ES050-Guadalquivir, ES07-Segura, ES080-Jucar,ES091-Ebro, ES100-Internal Basins of Catalonia, ES110- Balearic Islands, ES120-Gran Canaria. web link: http://servicios2.marm.es/sia/visualizacion/lda/recursos/superficiales_escorrentia.jsp (*Total water resources in the natural system (hm3/year) Average value for the period between 1941-2009) Reported to DG ENV for the Interim Report: PTRH3, PTRH4, PTRH5, PTRH6, PTRH7, PTRH8 WISE-SoE#3: all other RBDs / Eurostat JQ IWA: all Country level data to be checked on completeness and correctness

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To assess the balance between water availability and demand, and to identify water stress areas, indicators that capture elements of the water balance are useful and simple tools. The spatial and temporal scales of application of all such indicators, as well as their methods of calculation, are crucial yet cautious interpretation should be applied to avoid biased conclusions.

Research suggests that 20-50% of the mean annual river flow in different basins needs to be allocated to freshwater-dependent ecosystems to maintain them in fair conditions (Smakhtin, Revenga, and Döll 2004). Excluding this volume from the available for exploitation water may result in changing the severity level of water scarcity conditions. Returned water (into the same hydrological unit where abstraction occurs) can also affect the water stress level of an area. Depending, of course, on the water quality and location where the return occurs (e.g. upstream enough to be exploitable by other users downstream) this volume may be an important addition to the system alleviating potential problems, and thus needs to be taken into account when calculating the overall balance between availability and demand of a region to define the relevant water scarcity. Finally, the temporal scale of analysis of water stress conditions is important, since the problem may not be apparent at an annual scale yet be acute at seasonal scale, especially during summer where the availability is usually lower and the demand picks up.

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Box 4.1 the Water Exploitation Index+ (WEI+)

The Water Exploitation Index (WEI) was developed to formulate a harmonized message for awareness purposes on the state of the water resources, to provide an EU overview of water stress conditions, a hot spot analysis, and to be able to communicate the problem of overexploitation to other EU policy areas. Identifying the fact that the original WEI presented some limitations due to its simplified view of the water balance and its highly aggregated scale of implementation (i.e. country level), the EEA worked with the WFD CIS Expert Group on Water Scarcity & Drought towards an improved formulation of this indicator (the so called WEI+) with the purpose of better capturing the balance and critical thresholds between natural renewable water resources and abstraction, in order to assess the prevailing water stress conditions in a catchment. The proposed WEI+ aims mainly at redefining the actual potential water to be exploited (i.e. availability), since it incorporates returns and accounts for changes in storage, tackling as well issues of temporal and spatial scaling and proposing the use of environmental requirements for the formulation of adequate thresholds.

The WEI+ is formulated as follows: WEI+ = (Abstractions – Returns) / Renewable Water Resources

For the calculation of the Renewable Water Resources (RWR) two options have been suggested and selection relies on the available information and certainly (minimisation of bias) associated with each option.

Option 1 refers to the calculation of RWR based on the hydrological balance equation, using precipitation, external inflow, actual evapotranspiration and change in natural storage as components:

RWR = ExIn + P – Eta – ΔS

Option 2 refers to the calculation of RWR based on the naturalization of stream flow, using outflow, abstraction, return and change in artificial storage as components:

RWR = Outflow + (Abstraction – Return) – Δsart

Environmental Flows should be conceptually considered in the WEI+. At the moment, due to the absence of a harmonized and comparable method for calculation, eflows should be left out of the WEI+ formula itself, and be considered instead in the definition of the relevant thresholds. For more information on these thresholds: see Box 4.2.

Figure 4.7 Variability of the Water Exploitation Index (WEI+) at Morava RB in Czech Republic for the period 2005-2009 at monthly scale.

Source: EG WSD, provided by the representative of Czech Republic

To further enhance interpretation of the acuteness of water stress conditions, a satellite index to the WEI+ is proposed, defined as the ratio of water abstraction to the actual water use. This indicator can depict cases where water use is higher than abstraction and met by other means (e.g. desalination) so that freshwater resources are not overexploited, or cases where abstraction is much higher than the actual use due for instance to high losses.

Figure 4.8 Precipitation versus agricultural demand patterns

Source: Jucar Pilot RBMP

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Box 4.2 Environmental flows

Relevant thresholds / Will be written later

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To evaluate the state of water resources in a more analytical manner (as opposed to indicators which represent aggregated information), as well as their relation to the economy, water account’ approach provides an additionally useful tool. Water accounts focus on the quantitative assessment of the stocks and the changes in stocks which occur during the accounting period (e.g. month) and link information on the abstraction and discharge of water with information on the stocks of water resources in the environment. Thus they can describe the exchange of flows from the environment to the economy, within the economy, and from the economy to the environment allowing for the assessment of the pressure on water quantities exerted by the economy and the identification of the economic agents responsible for abstraction and discharge of water into the environment under different spatial scales.

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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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Note: Currently the methodology and data quality are in public consultation (organized by European Commission, DG Environment). Based on the reactions on this consultation, the Water Accounts maps will be recalculated and presented at a meeting at DG ENV on 7 September. The final maps will be included in this report as well.

This part has to be completed with a short explanation of the water accounts calculations, the data used (as these are not only the data provided by member states through Eionet), the data quality and proxy’s used.

This part will contain a / some map(s) with the results, focusing on availability, abstraction and water exploitation index and their interpretation / discussion of the results.

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Box 4.4 Groundwater quantitative status

The definition of good groundwater quantitative status according to the WFD requires that the level of groundwater in the groundwater body is such that the available groundwater resource is not exceeded by the long-term annual average rate of abstraction.

From the total number of Groundwater bodies reported in the WFD RBMPs, only 6% (672 Groundwater bodies) are classified as being in poor quantitative status in 2009. Only a few countries, namely Spain, United Kingdom, Belgium, Czech Republic, Germany, Italy, Malta, have groundwater quantitative problems which are though mainly found in specific RBDs and not in the whole country, with the exception of Cyprus where approximately 70% of its Groundwater bodies are in poor status (Map 4.3).

Map 4.3 Percent of Groundwater bodies in poor quantitative status in 2009 per RBD

Data source: WISE-WFD database, February 2012

There are four significant pressures that are affecting groundwater quantitative status based on the WFD. The most commonly reported pressures are water abstraction (in 11% of classified GWBs and 80% of GWBs which are in poor quantitative status), followed by saltwater intrusion (in 18 % of GWBs in poor status). Artificial recharges constitute a pressure in only 1% for GWBs in poor status and finally other pressures are responsible for about 5% of the GWBs in poor quantitative status (Figure 4.9).

Figure 4.9 Relevant pressures for GWBs

Data source: WISE-WFD database, February 2012

The main response measures across Member States (as identified in the WISE-WFD and the compliance check databases) are grouped into 11 categories, varying from voluntary, to regulatory, legislative and financial, as presented in Table 1.

Table 4.1 Groups of measures and popularity

Note: analysis based on 15 RBDs that in 2009 were in poor quantitative status but the projections for 2015 are showing significant improvement

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4.2.2.      Future evolutions of droughts and water scarcity

Future of evolutions of droughts are described in (EEA (report under preparation) 2012b). River flow droughts are projected to increase in frequency and severity in southern and south-eastern Europe, the United Kingdom, France, Benelux, southern Scandinavia and western parts of Germany over the coming decades (Feyen and Dankers 2009).

Climate change will affect not only water supply but also water demand. Socio-economic factors such as population growth, increased consumption, and land use have a huge impact on water scarcity with climate change exacerbating the problem. Water resources are expected to decrease in Europe as a result of increasing imbalance between water demand and water availability. Water scarcity, mainly due to the increased projections for irrigation, is projected to increase in many regions in Europe. How water demand can evolve and how this can impact water scarcity figures is described in EEA (2012b). Initial research suggests that climate change may also have some effect on household water demand (Keirle and Hayes 2007). The challenges for cities are described in EEA (2012c, section 2.3).Many cities in southern and eastern Europe, as well as some in western Europe are already experiencing water stress during the summer. Future projections see an aggravation and also northwards extension of the problem. When cities want to overcome regional water scarcity through imported water they become more dependent on other regions with implications for water pricing.

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4.3.    Floods occurrence

Through the ages and across Europe, damaging floods have been an ever-present peril to human settlements, and several studies have documented historical flood events in Europe going back several centuries (e.g. Brázdil, Kundzewicz, and Benito 2006; Bürger et al. 2006; Macdonald and Black 2010; Glaser et al. 2010). Most of the large-scale disastrous inland events have been caused by prolonged periods of heavy rainfall, often coinciding with ice-breaking or snow melt (Glaser et al. 2010). An important question for flood risk managers is to establish if the flood hazard has changed in recent decades. When discussing changes and trend in flooding it is important to distinguish between, on the one hand, changes in the occurrence of period of high river flood and (this section) and on the other hand, changes in economic damage resulting from inundation and destruction of infrastructure (section 5.2).

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4.3.1.      Changes in flood flow

Available evidence suggests different patterns across Europe with increasing high flows in northern Europe, especially in western Britain and coastal Scandinavia. Regional patterns are, however, diverse, with many weak negative trends occurring in northern Europe as well, and a very mixed pattern in central Europe. Detection of a climate signal in hydrological observations of flood magnitude and frequency is difficult due to the confounding effects of long-term natural variability in climate, human disturbance of catchments and river systems, as well as the relatively short period of observation in most rivers. Stahl et al. (2011) analysed trends in 7-day maximum flows and found that the overall pattern largely confirms the results of national studies, i.e. – increasing high flows in northern Europe, with steepest trends in western Britain and coastal Scandinavia, but regional patterns are very mixed, with many weak negative trends also occurring in northern Europe, and a very mixed pattern in central Europe (figure 4.10). Conclusions from such evidence-based studies are limited in spatial scope to the areas where observed long-term flow data exists and are made available. For example, no data from south eastern Europe was included in the study by Stahl et al. (2011)

Figure 4.10 7-day maximum trends across Europe, 1962 – 2004


Source: Stahl et al. 2011
Note: Blue circles denote positive trends, red circles negative, with trend magnitude expressed in standardized units.

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Climate variability associated with the North-Atlantic Oscillation (NAO) has been cited as a likely driver of observed high flow trends in some national-scale studies. In the UK, Hannaford and Marsh (2008) found relationships between the NAO index and high flow indicators in western Britain, which is likely to influence the upward trends seen in these areas. The NAO has also been posited as a mechanism for influencing stream flows in central Europe. For example, Villarini et al. (2012) found the NAO to be a significant factor explaining patterns of extreme flooding in Austria, although other studies from central Europe have been less conclusive (e.g. Schmocker-Fackel and Naef 2010). The association of flooding with modes of large-scale atmospheric circulation raises the question whether recent changes in flood frequency reflect anthropogenic climate change or the influence of multi-decadal variability. These two factors are not mutually exclusive, though, since modelling studies suggest that the recent evolution of large-scale patterns such as the NAO is also driven by anthropogenic forcing (Dong, Sutton, and Woollings 2010).

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4.3.2.      Future floods

Flood risk management needs to consider developments in both flood hazard and vulnerability. Scenarios for flood risk management thus have to combine socio-economic scenarios, such as projections for population growth, urbanisation and industrial developments with projections of future hazards resulting from a changing climate and hydrology. Recent studies (e.g. Dankers and Feyen 2009; Feyen et al. 2011) suggest that climate change can add significantly to expected damages in some parts of Europe over the coming decades. The scenarios of changes in flood hazard were combined with projections of socio-economic change. The results showed that the combination of climate change and economic growth will likely result in a strong increase in flood risks across Europe (Flörke et al. 2011). The ClimWatAdapt project focused on floods with an annual exceedance probability of 1% (equivalent to the predicted 100-year flood). The future scenarios showed that the occurrence of a 100-year flood event is strongly affected by climate change. However, the uncertainty related to the spatial distribution is still large, and different climate models gave very different results. Using the ensemble mean, the 100-year flood was projected to increase, especially in the north-western part of Europe and on the Iberian Peninsula (see also EEA (report under preparation) 2012b, section 3.3.3). Flash floods and urban floods, which are triggered by local intense precipitation events, are also likely to become more frequent throughout Europe (Christensen and Christensen 2002; Kundzewicz, Radziejewski, and Pínskwar 2006).

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When accounting only for climate change, some regions dominated by snowmelt (for example the Vistula and Odra catchments in Poland) are likely to see a reduction in annual flood damages due to the strong reduction in snowmelt-driven and ice-jamming floods, which compensates for the increase in summer flood damage in these regions.

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4.3.3.      Types of flooding

Most of the examples in this report are from rivers or ‘fluvial flooding’. But one has to keep in mind there are many sources of flooding, mechanisms of flooding and characteristics of the floods (WG F Drafting Group, Adamson, and Brättemark 2011). The main sources to be distinguished are:

-          Fluvial (rivers, drainage channels, mountain torrents and ephemeral water courses and lakes);

-          Pluvial (urban storm water, rural overland flow or excess water or floods arising from snowmelt);

-          Groundwater ;

-          Sea water (including estuaries and coastal lakes, e.g. due to extreme tidal level and/or storm surges or arising from wave action);

-          Artificial water-bearing infrastructure (failure of infrastructure including sewerage systems, water supply and wastewater treatment systems, artificial navigation channels and impoundments like dams and reservoirs).

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The main mechanisms of flooding are:

-          Natural exceedance;

-          Defence exceedance (overtopping defences);

-          Defence or infrastructural failure (could include breaching or collapse of a flood defence or retention structure but also failure in operation of pumping equipment or gates);

-          Blockage / restriction (flooding due to natural or artificial blockage or restriction of a conveyance channel, could include blockage of sewerage systems as well as restrictive channel structures such as bridges or culverts or arise from ice jams or landslides).

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The main characteristics, in relation to the vulnerability of the flooded area are:

-          Flash floods (quite rapidly rise and fall of the water level with little or no advance warning, usually the result of intense rainfall);

-          Snow melt flood (possibly in combination with rainfall or blockage due to ice jams);

-          Speed of onset (can be rapid, medium or slow);

-          Debris flow;

-          High velocity flood;

-          High water level (deep) flood.

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