Geoscience Reference
In-Depth Information
further reduction in human well-being, especially
for poorer people in lower-income countries.
Invasive alien species are important as they can
often cause very significant impacts on the riverine
and adjacent ecosystems, especially in floodplains
and deltas. It is worth noting that some alien
species may not be especially invasive, and actually
develop new species combinations, forming novel
ecosystems (Hobbs
et al.
, 2006; Marris, 2009) that
can deliver their own suite of services, and provide,
or restore, resilience and sustainability to river
ecosystems.
(before 1949), priority use for those with closer
access (1949-1986), ration planning (1987-1998)
and integrated management (1998 to present).
Analysis of data from 1959-2002 showed how
climate change affects natural flows. Since the
1990s the annual flow declined by 4.73 billion m
3
in Lanzhou, south Gansu province, an important
inflow area for the Yellow River (Wang
et al.
,
2005). During this period temperature showed
an increasing trend, accompanied by a decline of
average annual precipitation (Yao
et al.
, 2007).
These climate changes are amplified by human
disturbance in the area (Niu and Zhang, 2005; Yao
et al.
, 2007).
In addition, the Yellow River is the world's most
sand-laden river carrying 1.6 billion tons annually
(Yellow River Commission, 1998). Because of
silting caused by the sand load, the river bed is
rising by around 10 cm each year and some reaches
are now 4-6 m above the ground level, with the
highest 10 m. Despite the large volume of water
in the river, water scarcity is a serious problem in
the Yellow River basin. According to the Annual
Water Resource Report of the Yellow River, the
total annual flow in the river systems was 49.777
billion m
3
with human water use of 38.354 billion
m
3
, i.e. 77.05% (Yellow River Commission, 2008).
There are always interactions between natural
water resource changes and human activities,
including water diversions, unlimited groundwater
use and rain water collection. Currently water
retention in dams is 29.91 billion m
3
,orabout
60.92%, of the total outflow of the Yellow River
in 2008 while the total capacity of water reservoirs
in the basin is more than 72 billion m
3
. The largest
ecological event in the Yellow River basin was the
lack of flow to the sea during 22 of the years from
1972-1999, for a total of 1092 days.
The longest break was in 1997, when the river
had little or no flow to the sea for about 226
days, extending at some times up to 700 km
inland (Wu
et al.,
1998; Zhou and Chen, 1998).
This drought affected an area of 5.4
×
10
4
km
2
and 140 million people were at risk because of
water shortages. During the entire period from
1972-1996 an area 70.42
×
10
4
hm
2
was affected
resulting in reduced food production of around
Ecological flows and ecosystem
services: case studies
Changes in the state of rivers affect dramatically
their ability to provide ecosystem services - the
decline in the Tigris and Euphrates systems, the
Colorado river system in the USA, Murray-Darling
system in Australia and Aral Sea basin in central
Asia are obvious examples. Data from 925 large
global rivers (MA, 2005b) show that the runoff of
one third of these rivers has changed significantly.
Included in these 925 rivers were the Yangtze River
and the Yellow River from China. The following
two case studies illustrate the linkage between
ecological flows and the provision of ecosystem
services.
The Yellow River
The Yellow River flows for 5464 km to reach
the Pacific. Its annual outflow of the source
region in Qinghai-Tibet plateau is 24.87 billion m
3
,
contributing 40% of the total annual flow of the
Yellow River. Within the source region climate
change has had, and continues to have, a major
impact on the amount and quality of water in
the Yellow River. Under published scenarios for
climate change (Lin
et al
., 2006) the major threats
the region faces are melting glaciers, increase of
melting depth of permafrost, shrinkage of lakes and
wetlands, soil erosion, vegetation degradation and
desertification.
According to Yu (2006) water use in the Yellow
River basin experienced four stages as free use
