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

Figure IV.C.4. Potential impact of sea level rise on the Nile Delta. Assuming an extreme
sea level rise of 1.0 m over the next century, the impact on Egypt’s economy would be very
serious, with destruction of the protective sand belt and inundation of valuable agricultural
land. Sea level rise effect has accelerated in this area since the construction of the Aswan
dam. (Sources: Otto Simonett, UNEP/GRID Geneva; Prof. G. Sestini, Florence; Remote
Sensing Centre, Cairo; DIERCKE Weltwirschaftsatlas).
Under a scenario of doubling CO2, climate models are converging towards an
intensification of the hydrologic cycle with increase in precipitation intensity, up to 1%
per decade in the 20th century over the northern mid- and high latitudes, whereas
other areas in southern mid-latitudes are experiencing drier conditions (IPCC 2001).
However, the low levels of confidence still associated with model results and future
trends would tend to indicate more complexity in the interactions between climate
and the water cycle, acting differently at regional and seasonal scales. It is also
recognized that changes in the hydrologic cycle would emerge as extreme events in
time, either floods or droughts at specific periods of the year.
Increased rainfall with subsequent increase in freshwater runoff would enhance the
stratification of the water column in estuaries and adjacent coastal waters, leading to
a reduction in oxygen concentration at depth, often exacerbated by an excess of
organic matter in the upper layers. For example, observations revealed that the
levels of precipitation and river flow have been increasing over the Mississippi River
watershed during the last 100 years (Baldwin and Lall 1999), and are responsible for
a significant change in the physical structure and productivity of the Gulf of Mexico
(Donner et al. 2002). Similarly, winter precipitation has substantially increased over
Northern Europe, multiplying flooding events along river basins and increasing runoff
of freshwater into the North Sea (see Box # 1).
On the contrary, an analysis of hydrological data in the Baltic Sea over 100 years
(Winsor et al. 2001; Rodhe and Winsor 2003) showed no significant long-term trends
in river runoff and salinity although large fluctuations are observed on a time scale of
few years, as well as several decades. In this area, the effect of an increasing
precipitation rate may be compensated by an increase in evaporation due to global
warming, resulting in little change in net precipitation (Rutgersson et al. 2002).
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