Fresh water resources Portugal
The major rivers in Portugal are the Tagus, the Douro, the Guadiana and the Minho, which hydrological basins are shared with Spain, as is that of the river Lima. These shared basins occupy 264,560 km2: 56,930 km2 located in Portugal and 207,630 km2 in Spain. The exclusively national rivers are smaller and more irregular, the most important of which are the Vouga, the Mondego and the Sado (8).
The seasonal distribution of river discharge will change: discharge will concentrate in winter months and reduce in spring, summer and autumn. The relative magnitude of the impact of climate change on river discharge increases from the north to the south of the country (9). A reduction of low flow volumes up to −50 % was shown for the Tagus River in the period 2070-2099 compared with the reference period 1981-2010, in an assessment based on five climate (GCMs) and five hydrological models, and four different scenarios of climate change ranging from a low- to a high-end scenario of global warming (the so-called RCPs 2.6, 4.5, 6.0 and 8.5) (17).
The magnitude and frequency of floods will increase, particularly in the north, due to the concentration of precipitation in the winter season, and a predicted increase in frequency of heavy rainfall. Water quality will deteriorate, particularly in the south region, as a result of a rise in temperature and a reduction in river flows in the summer season. Groundwater tables will sink, especially in near-subsurface aquifers due to the expected reduction in the replenishing rate and the increase of the evaporation. There will also be an increase in saline contamination of coastal aquifers due to saline intrusion as a result of sea level rise (9).
The combined effect of changes in recharge, crop water demand and sea level rise on groundwater levels and flow into coastal wetlands was studied for three Mediterranean areas: the Central Algarve (Portugal), the Ebre Delta (Spain), and the Atlantic Sahel (Morocco) (16). This was done for combinations of a Regional Climate Model (RCM) and a driving Global Circulation Model (GCM) under the IPCC A1b climate scenario, for the periods 2020–2050 and 2069–2099, and compared with 1980–2010 (for the Portuguese and Moroccan sites) and 1960–1990 (for the Spanish site). According to the results:
- Crop water demand will increase steadily, causing 15–20 % additional evapotranspiration until 2100. For the Portuguese site, crop groundwater demand is expected to increase by 32 %.
- Groundwater recharge will decrease toward the end of the century (mean >25 %) in all three areas.
- The response of groundwater flow to the projected decreases in recharge and increases in pumping rates will be a strongly reduced outflow into the coastal wetlands.
- The impact of sea level rise is insignificant when compared to the decrease in recharge and increase in crop water demand: under many circumstances, intensive pumping near the coast is a more important trigger of seawater intrusion than sea level rise itself. For the Portuguese and Moroccan sites, seawater intrusion is predicted to occur largely as a consequence of increased pumping rates and lower recharge.
- In the long term, water availability in the three regions is projected to decrease substantially and, together with increasing water demands, may seriously affect the wellbeing of humans and ecosystems that depend on groundwater for their subsistence.
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 (10):
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.
Present situation in Europe
In the EU as a whole, energy production accounts for 44% of total water abstraction, primarily serving as cooling water. 24% of abstracted water is used in agriculture, 21% for public water supply and 11% for industrial purposes (3).
These EU-wide figures for sectoral water use mask strong regional differences, however. In southern Europe, for example, agriculture accounts for more than half of total national abstraction, rising to more than 80 % in some regions, while in western Europe more than half of water abstracted goes to energy production as cooling water. In northern EU Member States, agriculture's contribution to total water use varies from almost zero in a few countries, to over 30% in others (7). Almost 100% of cooling water used in energy production is restored to a water body. In contrast, the consumption of water through crop growth and evaporation typically means that only about 30% of water abstracted for agriculture is returned (3).
Currently, just two countries, Germany and France, account for more than 40% of European water abstraction by manufacturing industry (3).
In general, water is relatively abundant with a total freshwater resource across Europe of around 2270 km3/year. Moreover, only 13% of this resource is abstracted, suggesting that there is sufficient water available to meet demand. In many locations, however, overexploitation by a range of economic sectors poses a threat to Europe's water resources and demand often exceeds availability. As a consequence, problems of water scarcity are widely reported, with reduced river flows, lowered lake and groundwater levels and the drying up of wetlands becoming increasingly commonplace. This general reduction of the water resource also has a detrimental impact upon aquatic habitats and freshwater ecosystems. Furthermore, saline intrusion of over-pumped coastal aquifers is occurring increasingly throughout Europe, diminishing their quality and preventing subsequent use of the groundwater (3).
Virtually all abstraction for energy production and more than 75% of that abstracted for industry and agriculture comes from surface sources. For agriculture, however, groundwater's role as a source is probably underestimated due to illegal abstraction from wells. Groundwater is the predominant source (about 55%) for public water supply due to its generally higher quality than surface water. In addition, in some locations it provides a more reliable supply than surface water in the summer months (3).
Fresh water reservoirs
Currently about 7000 large dams are to be found across Europe, with a total capacity representing about 20% of the total freshwater resource (3). The number of large reservoirs is highest in Spain (ca 1200), Turkey (ca 610), Norway (ca 360) Italy (ca 570), France (ca 550), the United Kingdom (ca 500) and Sweden (ca 190). Europe's reservoirs have a total capacity of about 1400 km3or 20% of the overall available freshwater resource (6).
Three countries with relatively limited water resources, Romania, Spain and Turkey, are able to store more than 40% of their renewable resource. Another five countries, Bulgaria, Cyprus, Czech Republic, Sweden and Ukraine, have smaller but significant storage capacities (20–40%). The number and volume of reservoirs across Europe grew rapidly over the twentieth century. This rate has slowed considerably in recent years, primarily because most of the suitable river sites for damming have been used but also due to growing concerns over the environmental impacts of reservoirs (3).
Fresh water availability
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 (11).
Projected future situation in Europe
Appliance ownership data is not currently readily available for the new Member States but it is believed that rates are currently relatively low and likely to rise in the future. Higher income can also result in increased use and possession of luxury household water appliances such as power showers, jacuzzis and swimming pools. Changes in lifestyle, such as longer and more frequent baths and showers, more frequent use of washing machines and the desire for a green lawn during summer, can have a marked effect on household water use. The growth in supply within southern Europe has been driven, in part, by increasing demand from tourism. In Turkey, abstraction for public water supply has increased rapidly since the early 1990s, reflecting population growth and a rise in tourism (3).
Water stress over central and southern Europe is projected to increase. In the EU, the percentage of land area under high water stress is likely to increase from 19% today to 35% by the 2070s, by when the number of additional people affected is expected to be between 16 and 44 million. Furthermore, in southern Europe and some parts of central and eastern Europe, summer water flows may be reduced by up to 80% (4).
Runoff is estimated to increase north of 47°N by approximately 5-15% by the 2020s and 9-22% by the 2070s. North of 60°N, these ranges would be considerably higher, particularly in Finland and northern Russia (1). Average annual runoff in Europe varies widely, from less than 25 mm in southeast Spain to more than 3000 mm on the west coast of Norway. Climate change is thus going to make the distribution of water resources in Europe much more uneven than it is today. And even today's distribution is highly uneven, particularly considering the distribution of population density. Almost 20% of water resources are north of 60°N, while only 2% of people live there (2).
Not only will climate change affect the spatial distribution of water resources, but also their distribution in time. In northern Europe, the flows in winter (December to February) will increase two- to three-fold, while in spring they will attenuate considerably, in summer increase slightly and in autumn almost double by the period 2071-2100 (2).
EU policy orientations for future action
According to the EU, policy orientations for the way forward are (12):
- 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 (13), 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 (14,15). 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.
A number of measures exist that may potentially reduce the use of publicly supplied water. These can be broadly grouped into the categories of water saving devices; greywater re-use; rainwater harvesting and the efficient use of water in gardens and parks; leakage reduction; behavioural change through raising awareness; water pricing; and metering. Since treating, pumping and heating water consumes significant amounts of energy, using less publicly supplied water also reduces energy consumption (3).
In Denmark and Estonia, for example, a steady rise in the price of water since the early 1990s has resulted in a significant decline in household water use. Metering leads to reduced water use; in England and Wales, for example, people living in metered properties use, on average, 13% less water than those in unmetered homes (5).
Desalination increases the total available freshwater resource and, in this respect, may be preferable to further depletion of the surface and groundwater stocks. Detrimental environmental impacts are associated with desalination plants, however, in particular their energy consumption and the production of highly concentrated brine that may be released into sensitive marine waters. Furthermore, expanding supply from desalination plants does not provide any incentive to either reduce water use or improve the efficiency of use. Decisions on the suitability of future desalination plants need to be addressed on a case-by-case basis, accounting for all environmental and economic issues (3).
The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Portugal.
- Alcamo et al. (2007)
- Eisenreich (2005)
- EEA (2009)
- EEA, JRC and WHO (2008)
- Environment Agency (2008a), in: EEA (2009)
- EEA (2007), in: EEA (2009)
- IEEP (2000), in: EEA (2009)
- Portuguese Environment Agency with the cooperation of Ecoprogresso – Environment and Development Consultants, SA (2009)
- Portuguese Environment Agency with the cooperation of Ecoprogresso – Environment and Development Consultants, SA (2006)
- Kuusisto (2004)
- European Commission (DG Environment) (2007)
- Commission of the European Communities (2007)
- Faunt (2009), in: Taylor et al. (2012)
- Scanlon et al. (2012), in: Taylor et al. (2012)
- Sukhija (2008), in: Taylor et al. (2012)
- Stigter et al. (2014)
- Pechlivanidis et al. (2017)