River Ecology and Restoration - River Dynamics and Integrated River Management - page 643

natural events that have a negative impact on the structure and functions of a river ecosystem. The
relative stability, resistance, and resilience of an ecosystem determine their response to a disturbance.
Climate change may be illustrated with climate diagrams at meteorological stations. The climate diagram
was suggested by Walter (1985). In the diagram, temperature is plotted on the left vertical axis and
average total monthly precipitation on the right vertical axis. Temperature and precipitation are plotted
on different scales. Walter (1985) used 20 mm/month as equivalent to 10 ć for the U.S. and Europe, but
100 mm/month is used as equivalent to 10 ć for a tropical rain forest. In this topic, 30 mm/month
equivalent to 10 ć for China. Very useful information, such as the seasonal fluctuation of temperature and
precipitation, the duration and intensity of wet and dry seasons, and the percentage of the year in which
the average monthly temperature is above and below 0 ć , is summarized in this climate diagram. When
the precipitation line lies above the temperature line then, in theory, there should be enough moisture for
plants to grow. The potential evapotranspiration rate will exceed the precipitation if the temperature line
lies above the precipitation line. The more the temperature line moves up and away from the precipitation
line, the drier the climate will be.
Global climate change can be represented by the climate change in the Tibet Plateau, as it is the third
pole of the earth. The distributions of decade average monthly temperatures and total monthly precipitation
are shown in each diagram in Fig. 10.16. Between the 1960s and 1990s, the shape of the precipitation
and temperature distributions has stayed the same. However, the average temperature has risen by about
1 ć . The winter dry period which previously was from the beginning of October to the end of November,
has extended from the beginning of October to the middle of December. The ecology of rivers around the
world is affected by this climate change. As a consequence of global warming, continuous drought
occurred in northern China. Figure 10.17 shows that many poplar trees in the Kuye River basin, which is
a tributary of the Yellow River in northwestern China, were killed by continuous drought from 1997 to 2003.
Fig. 10.16 Climate diagrams for the Tibet Plateau (at Lhasa), in which average monthly temperature is plotted on
the left vertical axis and average total monthly precipitation on the right vertical axis (10 ć is equivalent to 30 mm of
precipitation)