It can be seen from Table 5 that for the ECM-OTS model, in the
forecasted 8 years of 2006-2013, only the relative error of runoff in
2009 exceeded 20%, and its forecasted qualified rate was 87.5%,
reaching the level A. Meanwhile, for the whole predicted years, the
relative error of runoff forecast that is less than 10% are 5 years,
accounting for 62.5%. While for the ECM-CEEMDAN model, only in 2009,
its forecasted relative error is 18.81% which is close to 20%. The
whole forecasted qualified rate was 100%. Although the ECM-CEEMDAN
model has the same as the ECM-OTS model, with the runoff forecast
relative error of 10% in 5 years, its relative error value tend to
smaller on the whole, which indicates that the overall forecast accuracy
of the ECM-CEEMDAN model is better. Moreover, the average relative error
of the ECM-CEEMDAN model is 8.59%, which is 2.7% lower than 11.29% of
the ECM-OTS model. This shows that the ECM-CEEMDAN model has the higher
forecast accuracy than the ECM-OTS model.
Furthermore, from the deterministic coefficient of runoff forecast, the
DC value of the ECM-OTS model is 0.842, which is the level B, while the
DC value of the ECM-CEEMDAN model is 0.901, reaching the level A. This
shows that the ECM-CEEMDAN model has the high degree of agreement
between the runoff forecasting process and the measured process.
- Conclusion
- The CEEMDAN method can reveal the periodic characteristics of
rainfall, runoff and sediment on the multi-time scales in the source
area of the Yellow River. These three variables have a good
correlation in the short and the medium periods. In addition, runoff
and sediment show a better synchronization in the trend item, which
reveals the law of periodic fluctuations of rainfall, runoff and
sediment.
- With the co-integration theory and ECM, the ECM-OTS model and the
ECM-CEEMDAN model are established. They can reveal the long-term
equilibrium and short-term fluctuations of the original sequence and
component sequence of rainfall, runoff and sediment in the source area
of the Yellow River, and also can effectively forecast the runoff in
this source area.
- Both the ECM-OTS model and the ECM-CEEMDAN model can well describe the
dynamic equilibrium relationship between rainfall, runoff and sediment
in the source area of the Yellow River. However, the forecast period
error of the ECM-CEEMDAN model is less than 20%, and its forecast
qualified rate can attains to 100%, and the accuracy reaches the
level A. Compared with the ECM-OTS model, it has the better
forecasting accuracy, which provides a new and more accurate runoff
forecasting method.