River networks evolution under multiple stresses: A geometric and structural fractal perspective

Accurately quantifying changes in river networks is essential for studying and assessing the environmental effects of such changes. The fractal method has become a popular and effective tool for describing and capturing river network changes. However, it is usually limited to the geometric fractal dimension (Dg), whereas the structural fractal dimension (Ds) is rarely used. Despite this, the Ds could capture crucial structural information, which the Dg does not, such as interconnections among rivers and the overall basin connectivity. In this study, we examined the evolution of Dg and Ds in the Qinhuai River Basin from the 1960s to 2016, revealing the changes in river networks under natural and anthropogenic stresses from both the traditional geometric and novel structural fractal analysis perspective. We also determined the key factors causing fractal variation and their contributions. The results showed that river networks possess both structural and geometric fractality, with values ranging from 1.484 to 1.287 and 1.615–1.514, respectively. The values of Dg and Ds both declined, with Ds declining at a higher rate, suggesting that the river network weakened and deteriorated. The variances of Dg and Ds attributed to urbanization were 0.3139 and 0.3103, respectively, more than thirty times and almost twice as much as the variance attributed to precipitation features. Urbanization was identified as the most significant factor influencing fractal dynamics. These findings advance the understanding of river network evolution from a novel fractal perspective and provide support for integrating river restoration with urban planning practices.