2.3 Study Steps
By using CEEMDAN method, the time series of rainfall, runoff and
sediment in the source area of the Yellow River are decomposed to obtain
IMF component sequences at different time scales. Furthermore, the
co-integration theory is used to construct the ECM for the original time
series (ECM-OTS) and the CEEMDAN component sequences (ECM-CEEMDAN), and
then the runoff is forecasted by ECM-OTS and ECM-CEEMDAN respectively.
Finally, the runoff forecasted value of each IMF component is
reconstructed to get the runoff forecasted value of ECM-CEEMDAN, and the
fitting value and forecast accuracy of these two ECM models are compared
to draw a conclusion. The flow chart of study steps is shown in Fig. 1.
Fig. 1 Flow Chart of Study Steps
- Results and Conclusion
- Data Source
The source area of the Yellow River refers to the area above the
Tangnaihai hydrological station, which is located in the northeast of
the Qinghai Tibet Plateau of China. The geographic coordinates are
between 95°50 ’~103°30’ E and 32°10
’~36°05’ N, the basin area is 122,000
km2, and the average annual runoff is 20.37 billion
m3. The water source is mainly supplied by rainfall,
followed by glacial snow melting water and groundwater. The change of
runoff in the source area of the Yellow River has a vital influence on
the change of water resources in the whole Yellow River Basin.
The measured rainfall, runoff and sediment time series from 1966 to 2013
at Tangnaihai hydrological station are shown as in Fig. 2.
Fig. 2 Time series of rainfall, runoff and sediment at Tangnaihai
station in the source area of the Yellow River
- CEEMDAN Decomposition
The CEEMDAN method is used to decompose the time series of rainfall,
runoff and sediment in the source area of the Yellow River for
multi-time scales. The decomposition results are shown in Fig. 3-5.
With the CEEMDAN method, the annual runoff, rainfall and sediment data
seires at Tangnaihai hydrological station from 1966 to 2013 are
decomposed into a fifth-order mode, including four IMF components and
one residual. It reflects the multi-time scale evolution characteristics
of rainfall, runoff, and sediment in the source area of the Yellow
River. The IMF1 component of each variable has the shortest period and
the highest frequency, and the period of other components gradually gets
longer and their frequency gradually decreases. The periodic changes of
the component time series are shown in Table 1.
Fig. 3 Time series of rainfall components in the source area of the
Yellow River
Fig. 4 Time series of runoff components in the source area of the Yellow
River
Fig. 5 Time series of sediment components in the source area of the
Yellow River
Table 1 Periodic changes of rainfall, runoff and sediment component time
series