Spatial-temporal changes in the longitudinal functional connectivity of river systems in the Taihu Plain, China

The longitudinal functional connectivity of river systems refers to the process-based connections between upstream and downstream areas and is fundamental to understanding the dynamic and nonlinear hydrological behaviour of river basins. However, the quantification of such connectivity remains a challenge due to the absence of a consensus on the appropriate data and methods, especially in delta plains. In this study, based on the difference between water level fluctuations at adjacent stations, a new and quantitative longitudinal functional connectivity index (LFCI) was developed for delta plains. Focusing on the Taihu Plain, we then analysed the spatial-temporal changes in the LFCI during 1960-2012 and investigated the correlations between the LFCI and climate change and human activities. We found that the decadal, annual and seasonal changes in the average LFCI all presented slightly increasing trends in the recent 50 period, but the annual average LFCI increased significantly after 1978; the average LFCIs in June, July, and August of the flood season were less than those in other months in the Taihu Plain. We also found that the spatial-temporal changes in the average LFCI exhibited larger differences at the subregional and station scales; those in the Wu-Cheng-Xi-Yu subregion were least, and the average LFCIs at stations near the borders of adjacent subregions were less than those at other stations. Moreover, we found that the average LFCI had significant correlations with precipitation, river density and water surface ratio. Our results were consistent with common sense facts, which demonstrated that the indicator developed in this study can quite effectively quantify the longitudinal functional connectivity of river systems in delta plains.