Fresh water resources Germany
Fresh water resources in numbers - Germany
Germany is a country rich in water; 2.2% of its surface area is covered by water. The water surface is comprised of eleven large rivers (Elbe, Danube, Rhine, Weser, Ems, Warnow/Peene, Elder, Schiel/Trave, Oder, Rhône, Maas). Natural lakes contribute approximately 0.85% of the surface area. Furthermore, Germany has 291 dams. Approximately 11.7% of the surface area are designated to drinking water protection and underlie restrictions of use to protect existing water resources (1).
The largest amount of water, approximately 56%, is used as cooling water by power authorities. Mining and industry together use approximately 18%. Approximately 13% of water use goes to public water supply. Agriculture and forestry use less than 1% of the water (1).
Momentarily, Germany’s water resources are judged as sufficient, since only approximately 24% of available resources are used (UBA, 2001). However, even today water shortages occur regularly in regions with unfavourable water balance (particularly Brandenburg). In particular, this region lacks water to keep the water level of rivers constant and to flood the pits remaining after strip mining (1).
Vulnerabilities - Germany - High and low flows
Among the potential negative impacts of climate change, the increased risk of flooding and the decrease in water supply during summer are of primary importance. These impacts are the result of an observed shift, which is expected to become more pronounced in future, of precipitation from summer to winter, as well as higher evaporation owing to increased temperature. Additionally, the probability of extreme rainfall events is increased particularly in winter and the duration of snow cover is projected to decrease (1).
Especially the central and eastern areas of Germany will suffer from a decreased supply of water in the summer months. The risk of drought increases and is accompanied by constraints in agriculture, forestry, energy supply and navigation, and possibly also in drinking water supply. A reduction of groundwater recharge is a further potential negative impact of climate change. Hitherto, constraints in drinking water supply due to climate change have not been expected, despite an increasing eutrophication in many areas (1).
As yet, water supply and distribution is not prepared for water shortages in summer. If no adaptation measures are implemented, the vulnerability of impacted regions (eastern Germany) will be “high”. In the remaining areas, vulnerability to water shortages is “moderate” (1).
The water quality of groundwater and surface water is at risk. Intense rainfall and flooding could flush pesticides, fertilisers, industrial chemicals and pathogens from sewage systems into lakes and rivers (7).
Rhine catchment - past (20th century)
During the 20th century precipitation during winter time has increased in the entire Rhine catchment (+ 10 to + 20%) (11). The increase was slightly less in the Alps. During the winter season (Nov-Apr) mean discharge tends to increase: + 10 to + 15 % for most gauging stations along the main stream of the Rhine (12). The same holds for the lowest 7-daily mean winter runoff:+ 15 to + 20 %. During summers, these parameters decrease by up to 8 %, mainly due to rising temperatures (more evaporation) combined with stagnating precipitation and coincident reduced snow volume in the Alps. Summer precipitation has hardly changed in the 20th century (between -5 to + 5 %) (12).
Rhine catchment - future (2050)
For the period 2021 - 2050 compared with 1961-1990, a continuous rise in temperature is projected up to +1 - +2°C for the entire Rhine catchment. In the south (Alps) it will tend to be greater than in the north. For this period no considerable changes in precipitation are projected in summer, whereas an increase is projected for the winter between 0 % and + 15% (11).
For the period 2021 - 2050 compared with 1961-1990, projected mean discharge and lowest 7-daily mean runoffin summer remains almost unchanged. Increased precipitation in winter which, due to rising temperatures increasingly occurs as rainfall, will lead to a rise of mean discharge by 0 % to + 20 %, and a rise of low flow in winter by 0 % to + 15 % (12).
Rhine catchment - future (2100)
Unlike the changes in precipitation stated until 2050, precipitation in the Rhine catchment in the second half of the 21st century will considerably fall during the summer months, mostly by -10 % and – 30 % (11). On this basis, falling mean runoff and low flow in summer is simulated in comparable orders of magnitude (12).
The increase in precipitation during the winter months projected until 2100 for the entire Rhine mostly ranges between + 5% to + 20 %. It lies above the values pointed out for the near future (0 % to 15 %) (11). The increase of the mean runoff and of low flow in winter largely corresponds to that of area precipitation (12).
Upper Danube - past (20th century)
No significant trends have been found towards an increase and/or decrease of mean annual discharge in the 20th century. For the lowest 7-day mean discharge, a significant increase has been found for the winter, whereas for the summer no statistically significant trend has been found (13).
Upper Danube - future (21st century)
Model projections show a moderate decrease of the discharge in summer for the near future (2021 - 2050), and a clear decrease for the distant future (2071–2100). The band of uncertainty is significantly wider, however, for the distant future than for the near future. The model projections show a change of the discharge regime from a snow regime towards a more rainfall-dominated regime. This is due to changes in the snow accumulation and snowmelt processes as a result of projected higher temperatures and the projected change of the precipitation regime (higher precipitation in winter time) in the future (13).
Vulnerabilities - Germany - River water temperature
Water temperature of the River Rhine is rising. It has been rising by over 2 °C in summer (near Koblenz) between 1978 and 2011 (15), an effect caused by an increase in annual mean air temperature and thermal discharges. Water temperature will continue to rise as a response to projected climate change.
An ensemble of (global and regional) climate models was used to produce a plausible range of projections for future water temperature in the Rhine. These projections are based on an intermediate scenario of climate change (the so-called SRES A1B scenario) for the near future (2021-2050) and far future (2071-2100). Future projections were compared with the period 1961-1990 (reference) (16).
With respect to 1961-1990 mean annual water temperature of the Rhine will rise due to climate change between +0.6 and +1.4 °C in the near future, and between +1.9 and +2.2 °C in the far future. Increase is highest in summer and lowest in spring. At the end of this century projected temperature rise is +2.7 to +3.4 °C in late summer and +0.4 to +1.3 °C in spring (16).
The maximum number of successive days with a water temperature above 27 °C increases from 4 days in the reference period (at Koblenz) to 10 days in the near future, and 17 days in the far future. These prolonged durations of periods with unusually high water temperatures may provoke changes in the food web and in the rates of biological processes in the Rhine (16).
Measures or new regulations regarding the thermal load plan for the Rhine may be needed in the future since the maximal allowed water temperature of the Rhine downstream of thermal discharges is currently 28 °C (17), and the impact of thermal pollution should be added to the climate change effect above. Currently, several power plants and industrial facilities lead their thermal discharges into the Rhine, leading to water temperature increases up to 1.4 °C (15). Higher water temperatures may negatively affect river ecology (18).
Observed hydrologic regime changes of Alpine rivers
Global warming affects precipitation volumes in the Alps, the contribution of rain and snow to these volumes, and the timing of snowmelt. An overall decrease in snow cover is observed during the 20th century for low- and mid-elevations. Trends are less significant at higher elevations, and snowpack even increased due to higher precipitation totals. These changes affect stream flow of mountain catchments. These changes were investigated for a large number of catchments over the period 1961–2005 in six Alpine countries (Austria, France, Germany, Italy, Slovenia and Switzerland), with catchment size varying mainly between 100 and 1000km2 (14).
Over the last decades, hydrologic regime of Alpine rivers has changed. These changes vary with the character of hydro-climatic regimes. During 1961–2005, all regimes show a consistent shift toward an earlier start of snowmelt flow, with a trend magnitude of 11 days, along with an increase of 18 days in the duration of the snowmelt season. Also, distinct differences have been observed between glacial- and snowmelt-dominated regimes, and mixed snowmelt–rainfall regimes (14):
- Pure glacial- and snowmelt-dominated regimes are found in the heart of the Alps. These hydrologic regimes are mainly controlled by the storage of precipitation as snow and ice during the cold months. Lowest flows occur between December and February, highest flows during spring and summer. For these regimes, winter droughts have become less severe: drought durations have decreased by an average of 25 days over 1961–2005 and volume deficits have decreased by an average of 47%. Glacial regimes, in particular, show a consistent behavior with a melting season shifted by a week earlier, an increase of 29% in the snowmelt volume, and an enhanced contribution of the glacier to the total stream flow of corresponding catchments.
- Mixed snowmelt–rainfall regimes are found in pre-alpine regions. They exhibit two low flow seasons: during the winter when part of the precipitation is stored as snowpack, and during the summer due to a combination of earlier snowpack shortage, lack of precipitation and high evapotranspiration. For these regimes, high flows are mainly driven by snowmelt during the spring and by abundant precipitation in autumn. For these regimes, winter droughts seem to have become more severe: volume deficit in the Southeastern Alps (mostly Slovenia) has increased by 10%.
Whether these trends are linked to climate change or to climate decadal variability remains an open question (14).
Fresh water resources in numbers - Europe
The total renewable freshwater resource of a country is the total volume of river run-off and groundwater recharge generated annually by precipitation within the country, plus the total volume of actual flow of rivers coming from neighbouring countries. This resource is supplemented by water stored in lakes, reservoirs, icecaps and fossil groundwater. Dividing the total renewable freshwater resource by the number of inhabitants leads to water availability per capita. Thirteen countries have less than 5,000 m3/capita/year while Nordic countries generally have the highest water resources per capita. The Mediterranean islands of Malta and Cyprus and the densely populated European countries (Germany, Poland, Spain and England and Wales) have the lowest water availability per capita. The water availability is an annual data which therefore does not reflect at all seasonal variations (5).
Europe: five lake categories
There are almost one and a half million lakes in Europe, if small water bodies with an area down to 0.001 km2 are included. The total area of lakes is over 200,000 km2; in addition the manmade reservoirs cover almost 100,000 km2. The response of European lakes to climate change can be discussed by dividing the lakes into five categories (4):
Deep, temperate lakes
Typical representatives of this class are e.g. Lakes Maggiore, Ohrid, Geneva and Constance with mean depths of 177, 164, 153 and 90 meters, respectively. Due to the great depth and relatively mild winters, there is usually no ice cover. The future climate change in Europe may suppress the turnover in deep lakes. This implies the enhancement of anoxic bottom conditions and an increased risk of eutrophication. The oxygen conditions can also be anticipated to deteriorate due to increased bacterial activity in deep waters and surficial bottom sediment.
Shallow, temperate lakes
Balaton (600 km2, 3 m) in Hungary and Müritz (114 km2, 8 m) in Germany belong to this class. Increasing water temperatures may result in intensified primary production and bacterial composition. The probability of harmful extreme events, e.g. mass production of blue-green algae, will increase. The impacts may extend to fish life; changes in species composition and reduced fish catches will be anticipated. The use of the expression 'thermal pollution' is well justified for these lakes.
Ladoga (17 670 km2, 51 m), Onega (9670 km2, 30 m) and Vänern (5670 km2, 27 m) are the largest in this class, being also the three largest lakes in Europe. This group includes about 120 lakes with an area exceeding 100 km2. Most lakes of the boreal zone mix from top to bottom during two mixing periods each year. Shortening of the ice cover period will be the most obvious consequence of climate change in these lakes. This could improve the oxygen conditions in winter and spring.
These are mainly small water bodies in northern Scandinavian mountains and in the tundra region. Arctic lakes are generally considered to be particularly sensitive to environmental changes. Melting permafrost may seriously threaten the ecosystems of arctic lakes. In some cases the whole lake may disappear as a consequence of ground thaw and enhanced evaporation.
To this class belong all high altitude lakes in central Europe and also those located in southern Scandinavia. Even if mountain lakes were connected by channels, physical and ecological constraints limit species migration between them. In a warming climate, there is no escape route; the only possibility for survival is adaptation.
Adaptation strategies - Overview
EU policy orientations for future action
According to the EU, policy orientations for the way forward are (6):
- Putting the right price tag on water;
- Allocating water and water-related funding more efficiently: Improving land-use planning, and Financing water efficiency;
- Improving drought risk management: Developing drought risk management plans, Developing an observatory and an early warning system on droughts, and Further optimising the use of the EU Solidarity Fund and European Mechanism for Civil Protection;
- Considering additional water supply infrastructures;
- Fostering water efficient technologies and practices;
- Fostering the emergence of a water-saving culture in Europe;
- Improve knowledge and data collection: A water scarcity and drought information system throughout Europe, and Research and technological development opportunities.
Managed aquifer recharge
Comprehensive management approaches to water resources that integrate ground water and surface water may greatly reduce human vulnerability to climate extremes and change, and promote global water and food security. Conjunctive uses of ground water and surface water that use surface water for irrigation and water supply during wet periods, and ground water during drought (8), are likely to prove essential. Managed aquifer recharge wherein excess surface water, desalinated water and treated waste water are stored in depleted aquifers could also supplement groundwater storage for use during droughts (9,10). Indeed, the use of aquifers as natural storage reservoirs avoids many of the problems of evaporative losses and ecosystem impacts associated with large, constructed surface-water reservoirs.
Adaptation strategies - Germany
Status of climate adaptation in Germany
There are very great differences between the individual Länderas far as the implementation of adaptation measures is concerned. Measures that have already been implemented are in the minority. They will probably not be sufficient to cope with the future challenges in the water management sector, for hardly any of them were introduced – even partially – on the basis of climate change considerations. As the impacts of climate change have hitherto played little or no role in the planning of measures, the water measurement sector in most Länder is not yet adapted to climate change (3).
In general, the water sector should be able to adapt to future climate impacts, since a full range of sufficient adaptation options are available, even if their implementation is mostly considered to be complicated. Saving water and rebuilding natural rivers are considered to be most effective in adapting to a multitude of uncertain impacts of climate change. However, adaptation measures in water supply and distribution can presumably not be implemented without special support (particularly financial resources). If the necessary adaptation measures are implemented, a reduction to “low” vulnerability of the water sector to climate change can be expected (1).
Ecosystems in Germany
Surface waters should be managed nature-oriented, and if necessary reconstructed (e.g. through the creation of flood plains or the revival of bayous), to sustain the natural capacity of ecosystems. The sensitivity of aquatic ecosystems to impacts of climate change decreases with improved water quality and ecological state of surface waters, as is already called for in the European Water Framework Directive (1).
Infrastructure in Germany
Infrastructure is needed so that rainwater can seep away locally, can be used in sprinkler irrigation or can be discharged into water bodies, via a separate sewage network and with no mixing with polluted or contaminated water (2).
Reservoirs, storage units and retention basins are important components of the water-resources-management infrastructure. Such retention systems are integrated, multifunctionally, within the overall water-resources management system, and within catchment areas for the drinking-water supply, hydroelectric systems and runoff management (water injection during low-water periods; flood protection) (2).
For water resources to be used multifunctionally in the framework of adaptation to climate change, however, adaptive reservoir-management methods must be applied. Such methods involve chronologically and spatially differentiated management of retention facilities, taking account of the natural-area and water-resources requirements of downstream users (2).
Water-use efficiency in Germany
Methods and techniques for enhancing water-use efficiency are (2):
- "Greywater", roof-runoff water and process water should be used for technical and industrial purposes that do not require water of drinking water quality;
- Water-saving methods should be refined, especially in the context of commercial/industrial production processes;
- Precautions should be taken to prevent water losses in the distribution network;
- More efficient methods should be used in cooling of power stations and in irrigation of agricultural land;
- Treated, microbiologically pure wastewater should be used for irrigating agricultural land.
The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Germany.
- Zebisch et al. (2005)
- Government of the Federal Republic of Germany (2010)
- Government of the Federal Republic of Germany (2006)
- Kuusisto (2004)
- European Commission (DG Environment) (2007)
- Commission of the European Communities (2007)
- Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (2009)
- Faunt (2009), in: Taylor et al. (2012)
- Scanlon et al. (2012), in: Taylor et al. (2012)
- Sukhija (2008), in: Taylor et al. (2012)
- Belz et al. (2007), in: International Commission for the Protection of the Rhine (ICPR) (2011)
- Görgen et al. (2010), in: International Commission for the Protection of the Rhine (ICPR) (2011)
- Klein et al. (2012)
- Bard et al. (2015)
- ICPR (2013a), in: Hardenbicker et al. (2017)
- Hardenbicker et al. (2017), in: Hardenbicker et al. (2017)
- LAWA-AO (2007), in: Hardenbicker et al. (2017)
- Hilton et al. (2006), in: Hardenbicker et al. (2017)