A conceptual framework for establishing the index system of ecological environment evaluation–A case study of the upper Hanjiang River, China

Index system is a vital tool for evaluating the ecological environment. In this study, we present a version of ecological hierarchy network (EHN) called “ecological-factor conceptual framework” for the organization of index system. This conceptual framework divides the complex ecological environment into four subsystems that all have explicit definitions or ranges, namely climate factors, soil-terrain factors, biology resource factors and human factors. Our framework makes the selection of indices more explicit and based on science, as well as more representative. Using the ecological-factor conceptual framework, we established an evaluation index system for the upper Hanjiang River in Shaanxi province, China. The index system contained fourteen indicators, such as average annual precipitation, elevation, biological abundance index, net primary productivity (NPP), highway net density and industrial wastewater emission. The ecological environment was comprehensively evaluated using spatial principal component analysis (SPCA). In addition, we used the matrix of principal components to quantitatively analyze the driving forces that affected the ecological environment. The results show that Hanzhong Downtown and Chenggu County had poor ecological environment with ecological environment index (EEI) values of −0.1459 and 0.3506, respectively. Areas that were rated as moderate, high and very high accounted for 86.07% of the study area. We found that human factors were the most important factors driving the deterioration of the ecological environment in the study area.