Measuring the hydrological longitudinal connectivity and its spatial response on urbanization in delta plains

Abstract

The variations of hydrological longitudinal connectivity are influenced by natural factors and human activities in the delta plain where many sluices are distributed in. Measuring the longitudinal connectivity changed by human controls (i.e. sluices) is still an open question. Besides, the spatial relationship between the longitudinal connectivity and urbanization is not clear. To this end, a reasonable indicator (Sluice Longitudinal Connectivity Index, SLCI), composed of sluice passage probability, passage efficiency, and cumulative effects of sluices, is proposed to detect the changes in the longitudinal connectivity in the flood and non-flood seasons. Based on this indicator, we took the Wu-Cheng-Xi-Yu region (WCXY) in China as a study region and detected the spatial impacts of the urbanization indices on the longitudinal connectivity by the geographically weighted regression. It is found that the average longitudinal connectivity in the non-flood season is 32% larger than that in the flood season in the WCXY region. The spatial distribution of the non-flood SLCI (values ≥ 0.6) is 26% larger than that of the flood SLCI. Spatially, the longitudinal connectivity is low (SLCI < 0.2) along the river and around the city where the sluices are distributed in. The longitudinal connectivity of the highly urbanized regions is lower than that of the lowly urbanized regions. Meanwhile, the relative effects of urbanization indices on the longitudinal connectivity can be sorted as follows: Landscape (69%) > Population (51%) > Economy (48%) in the non-flood season, and Population (88%) > Economy (63%) in the flood season.