Climate Change and the European Water Dimension - Agri ...

The climate in the Atlantic Region is wet and relatively mild. Many of the larger lakes
are situated near the coast so are either free of ice or only covered with ice for a few
days a year. Precipitation gradients in the Atlantic Region are typically very steep and
there is often a strong altitude (orographic) component to the rainfall. In the UK and
Ireland, the most striking meteorological contrast is between the wet west and the dry
east. These differences are most pronounced in winter where the average rainfall
recorded between 1961 and 1990 ranged from more than 500 mm in the west to less
than 200 mm in the east. Another important factor modulating the weather conditions
experienced in the region is the trajectory of the Gulf Stream in the Atlantic. The
warm water of the Gulf Stream reduces the severity of the winters experienced along
the western seaboard whilst the position of its north wall influences the trajectory of
storms in the western approaches (Taylor, 1996).
The coastal climate in Northern France, Flanders and the lowlands of Belgium, the
entire territory of The Netherlands, and the lowlands of the Northern Germany shows
greater contrasts of temperature than the climate in Britain. Further east and south, in
the uplands of eastern Belgium, Luxembourg and Central Germany, the distance
from the sea and the sporadic occurrence of continental influences or modifications
due to the relief in the neighborhood of mountain slopes, cause more pronounced
annual ranges of temperature, mainly on account of the progressive lowering of
winter temperatures. Winters are dry and relatively severe, and the absence of
snowfall is unusual. The shortness of the intermediate seasons, autumn and spring,
causes the transition to be more abrupt, and the contrasts of temperature more
noticeable.
The continental influence increases eastwards in the Northern Alpine Fore-land from
the Swiss part eastwards to the Austrian part. The climate of the Northern Alpine
Fore-land is in all parts mainly governed by the influence of the Alps. This is
especially the case during northerly flow due to the upwind effects which are not so
much a function of the relative difference in height but rather a function of the
distance, windwards of the base of the Alps (Wallén, 1977). The mean annual cloud
cover is as low as about 50% over the south slope of the Alps, but it amounts to 65%
over the north slope (European Daylighting Atlas, 1996).
The inner alpine regions are dry and have sunny valleys, and the scanty precipitation
is rather uniformly distributed over the year. Valleys, which are oriented from west to
east, receive considerably less precipitation, whereas the north south valleys may
receive abundant rainfall due to hill effects with northwesterly flow.
The Mediterranean climate has a typical seasonal rhythm strongly marked with
respect to temperature, precipitation and weather in general. Hot dry summers from
mid-May to mid-September and rainy, rather changeable, winters from November to
mid-March are separated by short autumn and spring seasons of rapid change in
weather conditions.
Due to climatic reasons, water scarcity is a general concern in many Mediterranean
countries. Broader variations in water resource availability across the Mediterranean
region, corresponds to three geographic groupings (Margat and Vallé, 2000):
Group 1: Mainly Northern Mediterranean countries (Portugal, Spain, France and
Monaco, Italy, Bosnia-Herzegovina, Croatia, Slovenia, F.R. of Yugoslavia, Albania,
Greece). Generally rich in water (above 3000 m 3 /year/cap) where total water demand
is stable, or even decreasing, without quantity shortage problems (except for short
periods of time, or drought cycles for localized areas), but having to face water
58