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2. biogeographic regions

2. Biogeographic Regions

The nature and impact of human interventions in the hydrological cycle will be influenced by a number of different factors and these will vary across the EEA area. Climate, geology, soil characteristics, topography, altitude, distance to the oceans and, not least, the historical and current land-use, play a major role regarding the amount of usable water.

Significance, as well as the effects, of a human intervention in the water cycle depend on ecological restrictions. Considering this, a regional-based process of priority evaluation for human interventions in the hydrological cycle was used, in which it was decided in the first case to use the Biogeographic Regions used by the European Topic Centre on Nature Conservation (ETC/NC) for some aspects of its workprogramme. The 6 Biogeographic Regions (Boreal, Atlantic, Continental, Alpine, Mediterranean, Macronesian) have been determined by the European Commission (EC) for the purpose of the Natura 2000 process required for the EC Habitats Directive. The definition of the 6 Biogeographic Regions was considered by the Commission to be adequate for political purposes though ecologically it is not precise enough. A more accurate map of ecological regions at a pan-European level is being prepared by the ETC/NC and contains some 30 classes.

The ETC/NC was consulted at the start of this project in order to obtain a consistent approach, where appropriate, between the various Topic Centres of the EEA on regional issues. However, this first overview demonstrates that an approach based on a finer regional scale would appear to be unavoidable.

Furthermore, from the hydrological standpoint, the biogeographical division of Europe does not seem to be logical due to the fact that hydrological characteristics and human pressures vary strongly within a biogeographic region (e.g. Atlantic region of France is separated into three parts). However, it does appear to be appropriate in some countries (e.g. Spain and Ireland). Different areas grouped in the same biogeographic region are sometimes not really comparable (e.g. Alps and Pyrénées are not equivalent and the Norwegian Atlantic region is more related to the Alpine region).

In the hydrological cycle, the geology, the pluviometric conditions, cultural reasons, the human pressure etc. seem to be more important than general climate and altitude, which control the biogeography. Regionalisation is necessary to establish comparability between different areas and nature of the land surface and subsurface and should be part of this classification. Hydrological regionalisation (flow regime classification) is well defined for the FRIEND area (FRIEND 1994). The monthly flow regimes in Europe are divided into 13 classes and their distribution has been mapped over Europe. As this study is further developed under the 1996 Subvention funded work programme we shall be exploring the advantages/disadvantages of biogeographical and hydrological classifications and will attempt to distil the best from each. However, for the purposes of this first phase of the project we persevered with the biogeographical approach.

At the end of this chapter the proposed map of the biogeographic regions used by the European Topic Centre on Nature Conservation and the maps of Austria, France and Norway with some country specific adaptations are given.

2.1. Country specific descriptions and relationship to biogeographic regions

2.1.1. Alpine/boreal

a) Norway

The main climatic gradients are west to east and the precipitation varies from up to 4000 mm/a in the West coast maximum zone to a minimum of <300 mm/a in the central mountain valleys. The country average is approximately 1400 mm with a runoff of 1200 mm.

East Norway is part of the Baltic shield, the western parts are influenced by the Caledonian buckling. All parts of Norway are strongly influenced by glacial and glaciofluvial processes. This results in a large number of lakes, short steep rivers in Western Norway, long rivers with moderate gradients in Eastern Norway, thin till-type soil cover over large areas and deep clay deposits under the upper marine limit exposed after the last ice age by isostatic uplift.

The arable land is, to a large degree, under the marine limit (~100-180 m asl) and the agricultural area is only 3 % of the total land area, while the forested area is approximately 30 %. The rest is high elevation and/or latitude, fairly barren ground, and approximately 1 % is glaciated. The cultivated area is mainly confined to a narrow strip around the coast and to the inland areas north of Oslo (especially the river Glomma) and around Trondheim. A significant portion of the forested area has low production potential and low harvesting rates, and generally the level of forest cultivation (draining, ploughing, fertilising, replanting etc.) is lower than for instance in Sweden.

2.1.2. Alpine Region

a) Austria

The Alpine region in Austria coincides with the delimitation of the biogeographic regions outlined by the European Topic Centre on Nature Conservation.

b) France

It was considered that the Alps and the Pyrénées should perhaps be distinguished in terms of the interventions. The major intervention is damming for hydropower, but types of reservoir management and the effects of the damming are very different in the two mountain chains. In the Pyrénées, which can be considered much narrower and steeper than the Alps, water is often dammed and then transferred by long chutes to valley power stations, significantly reducing flow discharge in the mountain torrents. In the Alps, large reservoirs with adjacent power stations are more common, and they also control subsequent flows in many of the rivers flowing to the Mediterranean.

2.1.3. AtlanticRegion

a) Denmark

Western Jutland is classified in the Atlantic region in the biogeographic system. It is generally characterised by sandy soils with poor buffering capacity and relatively high precipitation (770 mm) and river flow (430 mm ~ 14 l.sec-1 km-2).

b) France

The Atlantic region in France actually comprises three very distinct regions in terms of human interventions:

  • The Southwest, where irrigation and water scarcity are important factors.

  • The Northwest, which has been extended to include the Atlantic-influenced Massif Central. In this area, river flow regulation is important (in particular the Loire) in order to satisfy many diverse uses (hydropower, irrigation, sufficient flows for cooling water etc.) and there are several significantly modified estuaries (for flood control, navigation etc.). Interventions in the form of dikes and embankments on the river Loire is also important in this area.

  • The North, where groundwater resources are under pressure in the Parisian to Lille (north-east) areas, generally due to poor surface water quality. Channelisation of the river Seine for navigation and flow regulation for water supply are significant interventions.

c) Portugal

The Atlantic region in Portugal is a very thin coastal strip north of the mouth of the river Tejo. It is generally characterised by cambisols, high rainfall (annual mean 2,000 mm) and river flow (annual mean 1,200 mm ~ 38 l.sec.km2). Irrigation is very intensive and population density is high. Groundwater resources are essential for domestic and industrial water supply and irrigation even though this region does not have major aquifers.

2.1.4. Continental Region

a) Austria

The Continental region in Austria coincides with the delimitation of the biogeographic regions outlined by the European Topic Centre on Nature Conservation.

b) Denmark

Eastern Denmark belongs to the Continental region and is generally characterised by more loamy soils with a high buffering capacity and relatively low precipitation (570 mm) and river flow (170 mm ~ 5 l.sec/km-2).

c) France

The Continental region in France includes the Rhône corridor. It also includes the east of the country, but excludes the Atlantic-influenced Massif Central. In addition the very important upstream reservoirs of the Seine in this area are included. These are involved in flood defence, low flow enhancement, public water supply and downstream cooling water resources for the whole river Seine catchment.

2.1.5. Mediterranean region

a) France

With one notable exception, the French Mediterranean biogeographic region is a reasonably homogeneous area. The exception is the river Rhône, which is in fact a major continental river (it just happens to flow towards the sea through a Mediterranean region). The Rhône corridor contains an important chain of runoff-river hydropower dams, which also have other functions (diversion of water, navigation, flood control etc.). For the purposes of this project, the Rhône has been classified with the Continental region although, in reality it is a special case all of its own

The Mediterranean region comprises many lagoons (especially the Rhône delta area) where a number of major interventions in terms of flood control and drainage have been carried out. These are considered significant interventions because of their value as wetland habitats.

b) Portugal

Although being usually considered as almost entirely included in the Mediterranean region of Europe, the Portuguese territory, due to its latitudinal configuration, presents an increase in dry-climate severity patterns from north to south, a feature in common with other Mediterranean countries like Spain and Italy.

The Portuguese weather is characterised by two well-differentiated annual periods, dry season and wet season. The dry season occurs between May and September and the rest of the year belongs to the wet season. The dry and wet seasons are also characterised by high and low temperatures, respectively. The irregular temporal distribution of precipitation during the year is more evident in the south of Portugal which causes greater scarcity of water in this region. This makes dam building indispensable in order to assure public water supply with increased water demand, and irrigation during the dry season

The Mediterranean region is not a homogeneous area. In terms of surface water characteristics it may be divided into two main zones with the Tejo river acting as a natural border:

  • northern part of Portugal (between Atlantic region and Tejo river) includes both an Atlantic-influenced and a Continental-influenced zone. In this area, river flow regulation is important in order to satisfy several uses such as hydropower, irrigation, water supply, recreation and fish farming.

  • southern part of Portugal (below Tejo river to Algarve) where irrigation and water scarcity are important factors. The main uses of reservoirs are for public water supply and irrigation.

In terms of groundwater the Mediterranean region can be divided into four main zones:

  • three zones of sedimentary rocks that correspond to: the occidental sedimentary fringe, the meridional sedimentary fringe, and the Tejo-Sado sedimentary basin. These zones constitute the main aquifer systems of Portugal.

  • one zone covered by igneous and metamorphic rocks with low aquifer capacities, which corresponds to the main area of the country.

All these aquifer systems are important for public and industrial water supply and for irrigation and constitute the main source of water for these uses.

In the Algarve region the pressure on groundwater resources, sometimes important and significant, provokes local problems of salt water intrusion. Groundwater pollution by nitrates from intensive agriculture is a further problem in this region.

The following pages show the specific maps of the biogeographical regions:

Figure 2.1 Biogeographic Regions defined by the European Commission for Natura 2000

Figure 2.2: Biogeographic Regions of Austria

Figure 2.3 Biogeographic Regions of Norway

Figure 2.4 Biogeographic Regions of France

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