Zheng, J; Zhang, W; Zhang, P, and Zhu, Y., 2014. Understanding space–time patterns of long-term tidal fluctuation over the Pearl River delta, South China.

Principal component analyses (PCA) were used to identify the space–time patterns of long-term tidal fluctuation in the Pearl River delta (PRD) region. The tidal levels of the 35 stations over the entire PRD were divided into four regions by the PCA. The results show that different regions display different trends, indicating spatial variability of long-term tidal fluctuations in PRD region. The regional pattern of the first component loadings is mainly located near the outlets. Time series of the factor scores of the the first principal component (PC) shows a significant increasing trend. The regional pattern of the second component loadings is concentrated in the upper part of the PRD region. The factor scores of the the second PC, however, display a significant deceasing trend. The trend in the factor scores of the the third PC of the middle part of the North River is not significant, but it has to face the highest flood risk. As for the upper part of the East River, the factor scores of the the fourth PC also show a significant downward trend that demonstrates that the tidal level shows an obviously decreasing trend in the upper part of the East River. The impacts of the intensive human activities on these changes in the PRD region in the latest three decades are the dominant factor. In particular, the large-scale and long-term sand excavation in the whole PRD region directly results in the riverbed down-cutting, leading to the tidal level in the upper part of the delta decreasing obviously. More tidal prism can enter the delta much more easily also due to the sand excavation, which can fill out the volume not only to keep the tide level, but also even increase the tide level in the middle part of the North River. What's more, intensive reclamation in the estuary is another main factor for tide increase at the outlets of the PRD region.