Geoscience Reference
In-Depth Information
water management in the region. The potential
consequences of more frequent and longer
droughts include an increase in desertification, a
decrease in water availability for food production
and new threats to human health, ecosystems and
the economies of affected countries. At a strategic
scale, the construction of dams and reservoirs is
a way of increasing the volume and reliability
of water supplies for agricultural and urban use.
However, dams disrupt significantly the natural
hydrological and fluvial morphological processes
that control habitat structure, the intensity and
frequency of floods, floodplain connectivity and
water quality conditions (Bunn and Arthington,
2002). The cumulative effect of small-scale local
modifications to the river channel and water flow
can have equally adverse effects on the special type
of freshwater ecosystem represented by temporary
streams. For example, the physical disturbance and
modification of temporary streams is widespread
in Mediterranean regions where local people rely
on streams and rivers for their water supply and to
graze their livestock in the dry periods (Gasith and
Resh, 1999).
Action to tackle one problem often leads
to adverse effects on other sectors of society;
therefore, a wide range of interests needs to be
taken into account when managing land and water
within a river catchment (Lee and Dinar, 1996).
Involving a range of stakeholders in the planning
and decision-making process is important and
this is a key principle enshrined in the European
Water Framework Directive (WFD; Council of
the European Communities, 2000; Leal, 2006).
However, the technical guidance for the WFD
does not refer explicitly to temporary, seasonally
intermittent streams; aiming to achieve 'good
ecological status' is more readily associated with
permanent watercourses. Therefore, securing the
full environmental benefits expected from the
WFD by December 2015 is a major challenge
for Mediterranean countries. For example,
monitoring methods and assessment protocols
need to take account of the seasonal and between-
year variations in assessment programmes for
temporary watercourses, not only to safeguard
water supplies for human use but also to conserve
ecological interest and integrity. This means it is
important to develop effective decision-support
tools for catchments with temporary streams,
particularly as climate change is very likely to
increase pressure on already scarce water resources
(Weiß
et al
., 2007).
Several catchment-based land and water quality
models have been developed in the past 20 years
(Lenzi and Di Luzio, 1997; Lowrance
et al
., 2000;
Cerucci and Conrad, 2003; Gassman
et al
., 2007).
These have explored the impact of land-use change
on water conditions, notably The Soil and Water
Assessment Tool (SWAT) which was developed
by the US Agricultural Research Service as a
multi-disciplinary catchment modelling tool. SWAT
has over 30 years of practical use for stream-
flow calibration and analyses associated with
pollutant loading and climate change impacts on
hydrology (Gassman
et al
., 2007). However, the
assumptions used in these models are based on
permanent watercourses, so their application in
catchments where streams are dry for part of
the year is limited (Trancoso
et al
., 2009). A
study of the effects of climate change on stream
hydrology was carried out in a demonstration
river catchment in southern Portugal to improve
current knowledge about temporary watercourses.
The main objectives of this research were: (i)
to study long-term patterns and trends of air
temperature and precipitation; (ii) to use the
SWAT model to simulate total runoff and discharge
across the entire catchment; and (iii) to develop
practical management guidance for implementing
conservation strategies.
Study area
The study area was the Pardiela catchment in
southern Portugal. The Pardiela is a fourth-order
Mediterranean stream with a catchment area of
514 km
2
(Figure 22.1a). The altitude range is from
505 m in the headwaters to 169 m, at its confluence
with the Degebe River (Gallart
et al.
, 2008). Mean
air temperature ranges from 9
◦
C in winter to 23
◦
C
in summer, with a mean annual precipitation of
600 mm (Lillebø
et al.
, 2007). The Pardiela has
a typical Mediterranean hydrological regime, with
low discharge in the dry summer period and high
