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

climate the thermocline will develop earlier in spring and disappear later in autumn.
Higher lake temperatures may greatly affect drinking water quality in terms of taste,
odour and colour (Sweden’s, 2001).
Model simulations reveal a general increase in the precipitation in Northern Europe
with a large increase in winter precipitation. The greatest increases in both
precipitation and net precipitation-evaporation difference (approximate measure of
water availability) are foreseen along the Atlantic coast and in Northern Scandinavia.
A slight decline is predicted in southeastern Sweden, however. The predicted
changes in precipitation vary in a larger range, which illustrates the uncertainties
involved in impact studies.
The estimated changes in water supply largely conform to the changes in
precipitation-evaporation: increased water supply in the north, but no clear change or
decrease in the south. One important conclusion to date is that the characteristic
spring flood of today will be more irregular and less intense, on average. This is
because the snow period will be shorter and the snow depth less due to the warming
effect. However, the water supply is expected to increase in winter and also in
autumn as a result of heavier precipitation. Accordingly, the risk of flooding will
diminish in spring but increase in late summer and autumn, particularly in the north
(Sweden’s, 2001).
A preliminary simulation of the regional climate scenarios indicates a clear increase
in surface water temperature in the North in spring and late summer and one month
shorter ice cover period compared to today’s climate. This will have implications for
the mixing regime, as dimictic lakes become monomictic with wide consequences for
nutrient and phytoplankton dynamics. The increase in surface water temperature in
summer implies an increase in summer stratification length with alterations in the
composition of summer phytoplankton blooms (unpublished results).
The scenarios (Räisänen et al., 2004) indicate that climate change may have a
dramatic impact on the Swedish environment. The rapid changes predicted in these
scenarios include a rise in mean temperature of about 0.4°C per 10-year period.
Precipitation is also forecast to rise by up to 2 per cent per decade. The climate
zones determining the range of the various biomes may move north by 50 to 80
kilometres a decade (Sweden’s, 2001).
In the Alpine region, future temperature change will exert a significant influence on
the hydrological cycle because temperature regulates how much of the precipitation
falls as rain or snow. Higher temperatures in winter reduce the amount of spring
snowmelt, raise the evaporation, and hence reduce run-off in spring. Temperature
increase leads to an expansion of the vegetation period and increases transpiration
reducing discharge. On the other hand, glacial melting is enhanced leading to greater
discharge during summer. In general temperatures will increase in most areas of
Austria while precipitation will decrease.
Similar to northern Europe, the Mediterranean region will warm at a rate of between
0.1 and 0.4ºC/decade (Haas, 2002). Projections point to more precipitation in the
winter and less in summer over the region as a whole, while mean annual
precipitation is expected to decline south of 45°N. The general tendency would be
that northern parts of the Mediterranean would become wetter, and the southern
parts drier, thus amplifying current rainfall differences and water scarcity. The IPCC
(2001) nonetheless acknowledges that the regional averages also mask important
basin-specific and temporal problems with distribution. Because the general
circulation models used to assess global and regional variations do not have
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