Water resources vary widely across Europe. Renewable freshwater
resources available for use in a country is the amount of water
moving in rivers and aquifers, originating either from local precipitation
over the country itself, or by water received from
neighbouring countries in transboundary rivers and aquifers.
A river is a system comprising both the main course and all the tributaries
that feed into it; the area that the river system drains is
known as the catchment. The main characteristic of rivers is their
continuous one-way flow in response to gravity. In addition,
because of changes in physical conditions such as slope and bedrock
geology, rivers are dynamic and may change nature several
times during their course (e.g., from a fast-flowing mountain stream
to wide, deep, slowly flowing lowland river).
When assessing river characteristics and water quality it is important
to bear in mind that a river comprises not only the course, but
also a vast number of tributaries. Rivers are greatly influenced by
the characteristics of the catchment area. The climatic conditions influence
the water flow, as does bedrock geology and soil type. The latter also
affects the mineral content of the river water. Human activity affects
river systems in numerous ways, for example, through afforestation or deforestation,
urbanisation, agricultural development, land drainage, pollutant discharge,
and flow regulation (dams, channelisation, etc.). The lakes, reservoirs
and wetlands in a river system attenuate the natural fluctuation in discharge
and serve as settling tanks for material transported by the rivers. Water
flow and water quality are therefore the net result of the various characteristics
of the catchment.
Future water supplies may also be adversely affected by climate change.
Potential climate change resulting from anthropogenic
emissions of carbon dioxide and other greenhouse gases is a major environmental
issue. The assessment of the Intergovernmental
Panel on Climate Change (IPCC) in 1995 is that the balance of evidence
suggests a discernible human influence on global climate.
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