Geoscience Reference
In-Depth Information
of 2005. By then, the channel course could only
be distinguished by the outline of fringing riparian
vegetation (Figure 22.1b).
to develop policies and management practices
that will not only safeguard human health, but
also maintain and conserve the ecological status
of temporary rivers. However, the between-year
variation in precipitation, combined with trends
of increasing temperature, decreasing rainfall and
greater human demand for water means that
sustainable ecosystem management is particularly
difficult in Mediterranean regions (Baron
et al.
,
2002). Improved hydrological models are needed
to predict with greater confidence the amount of
water available and the ecological consequences
associated with different scenarios of climate
change so that conservation strategies and water
management
Discussion
The Ribeira da Pardiela catchment demonstrates
the broad characteristics and problems of
temporary rivers in the Mediterranean region.
Evidence for increasing mean annual air
temperature and decreasing mean annual
precipitation detected in the catchment
reflects similar findings from other parts of the
Mediterranean and could lead to major problems
being experienced elsewhere. For example, Blad e
and Castro-Dıez (2010) found evidence for an
overall decrease in precipitation over the entire
Mediterranean region, but particularly in north-
west Africa, the southern Iberian Peninsula,
Italy, the Balkans and Turkey; this has resulted
in reduced availability of water for surface and
underground aquifer systems. Several authors
have predicted that by the 2070s there could be
a decrease in annual runoff of up to 36% in the
south (Alcamo
et al
., 2007), increasing the drought
risk in western and southern Europe (Lehner
et al
.,
2006).
Headwater tributaries in the Mediterranean
region usually flow only following consecutive
days of rainfall that is sufficient to saturate the
soil. At other times the channel is naturally dry.
However, the natural flow regime in the middle
and lower reaches is affected significantly by
water abstraction, particularly for agriculture. This
is a particular problem during the dry period,
when unregulated water abstraction, together with
livestock roaming along the stream bed damage
in-channel habitats. In some cases there are also
health risks associated with poor water quality.
These factors, and water abstraction in particular,
may have caused the channel in the study site to
narrow between 1958 and 2005 (Figure 22.1b).
Given that the most likely impacts of climate
change in Mediterranean regions will affect the
availability
practices
are
complementary
and
effective.
Mediterranean rivers are valuable ecosystems
that have been recognized as one of the foremost
25 'global biodiversity hotspots' (Myers
et al.
,
2000). Action needs to be taken at the landscape
level to safeguard this ecological interest. In
Portugal, landowners have the responsibility for
maintaining rivers by clearing the stream bed and
channel margins, but in an uncontrolled fashion
this has resulted in unsustainable use of water
and river landscapes. A catchment management
approach, applying the principles of the WFD
(Council of the European Communities, 2000), is
therefore required to protect the special character
and ecological value of temporary Mediterranean
streams and their corridors. To illustrate the
practical aspects and benefits of sustainable
management a small number of demonstration
catchments could be used to apply practical
conservation strategies which could then be tested
and monitored at relatively low cost. These
conservation strategies should reflect sustainable
development principles, balancing human needs
and ecosystem health and exploiting the benefits
provided by traditional land management such as
holm oak forest and olive groves. Special attention
should be focused on the problems caused by
water abstraction and livestock damage to the
river channel and margins. Using the experiences
of physical and biological problems from other
similar catchments (G omez
et al
., 1995, 2005),
of
water
it
is
extremely
important
