1. INTRODUCTION
Owing to the continuous growth of the human population, social productivity demands associated with development are rapidly increasing in many countries (Liu and Diamond, 2005). However, demands for the protection of water resources and ecological environments restrict development (Bian et al., 2022; Jiang et al., 2022). Water conservancy projects are essential for flood control, water storage, sediment retention, and enhancement of agricultural production. The interference of human activities on the ecological environments have been gradually amplified (Zeng et al., 2022; Zhu et al., 2017). Such projects enhance production and the standard of living in many regions. However, they also impact hydrological processes and damage nature in associated basins (Xu et al., 2022). For example, regardless of its benefits, flood control, directly or indirectly affects the natural water cycle and causes ecological changes in basins (Ding et al., 2020; Du et al., 2019).
Previous studies on water conservancy projects focused on the hydrological response to changes in runoff and impacts on the water ecological environment (Sun et al., 2019; Wu et al., 2019). For example, Assani et al. (2011) showed that changes associated with a water conservancy project on runoff in a basin differed from those caused by climate change. These obvious differences indicate that a water conservancy project represents an in–dependent factor that controls runoff changes in a basin. Based on several models, Callow and Smettem (2009) indicated that the construction of small water diversion embankments and collection infrastructures significantly impacted runoff changes in areas of major agricultural activities in Italy. Schreider et al. (2009) investigated 12 basins, including that of the Jamieson River in Mexico, and noted that the construction of dams in farming areas significantly affected runoff and its changes in basins. Flood forecasting and sediment transport in basins following water conservancy projects have been reported in many studies. Analyses of changes in water and sediment flow in response to varying driving factors have improved our understanding of the evolution of hydrological regimes associated with floods in basins and impacts on water and soil loss prevention (Roberta et al., 2022; Yuan et al., 2014). Considering the evolution of hydraulic engineering facilities and the paucity of records, a detailed characterization of the impacts of such facilities on runoff is challenging (Sarah et al., 2022). Therefore, hydraulic engineering modules have been incorporated into many simulators, and this has been exploited in many studies on hydrological modeling (Wu et al., 2020). Cao et al. (2019) incorporated water conservancy projects to explore trends in flooding based on basin hydrological models, and this significantly improved the accuracy of flood forecasting. Xiong et al. (2020) used a hydrological model and field data to explore changes in flooding and the ecological environment of a basin. GIS technology has been increasingly employed in the construction of distributed hydrological models for the characterization of ecological changes in basins (Lyu et al., 2019). Therefore, based on a distributed hydrological model, Guo et al. (2022) explored the impacts of the construction of check dams on ecological changes in the Loess Plateau. The increasing water conservancy projects are exacerbating the changes to the ecology in the plateau region; these changes elevate uncertainties in results from different studies (Wu et al., 2017). Comprehensive evaluation of the impact of water conservancy projects on the regional ecological environment is an important research topic.
The Loess Plateau is in the hinterland of Eurasia and is an important area of agricultural production in China. The ecology of the region is fragile because of the limited natural endowment of water resources and severe soil erosion. Therefore, as a prominent area in China that requires ecological protection, several water and soil conservation measures, including forest and grass measures and engineering measures, have been implemented in the region since the 1970s (Wu et al., 2017). Forest and grass measures can fundamentally prevent water and soil loss (Wang et al., 2016). However, the effects of the implementation of forest and grass measures on water and soil loss control cannot be immediately observed. Surveys indicate that afforestation to sediment reduction measures require 3–5 years to be effective. The benefits of engineering measures such as reservoirs in flood detention and sediment reduction are more obvious than those of forest and grass measures (Wu et al., 2018). Thus, construction of reservoirs can provide certain ecological benefits for the regional environment (Nilsson et al., 2005). These measures were intended to prevent deterioration of the regional environment, increase its ecological bearing capacity, and ensure a balance between development by humans and the conservation of nature. However, interference from human activities complicates the ecological environment and hydrological cycle in the region (Yang et al., 2004; Li et al., 2018; Guo et al., 2022). Therefore, evaluation of the extent and impacts of human activities on hydrological processes and the ecological environment, as well as shaping and preserving ecological stability in the basins under new water and sediment conditions associated with water conservancy projects, are gaining increasing attention in basin ecology and hydrology studies (Wen et al., 2022;Kang et al., 2021).
The Qinhe River Basin is part of the Shanxi Plate in the Loess Plateau. The upper and middle reaches of the basin are valley landforms, where flood disasters frequently aggravate water and soil loss. (Wang et al., 2006). The lower reaches are important areas for agricultural activities. According to Lyu (2006), cultivated land occupies approximately 26% of the drainage area but is under increasing pressure because of the increasing population and urbanization. Considering the safety of agricultural production and human life, many reservoirs have been constructed that have been implemented in the basin since the 1950s. The primary objectives of these measures were to mitigate ecological deterioration and water and soil loss (Wang et al., 2016). However, because of its complexity, the relationships between human activities and the ecology in the basin remain uncertain. The construction of reservoirs creates challenges in the assessment of trends in ecological and driving factors of changes in the basin (Zhang et al., 2011; Lv et al., 2018). Therefore, the achievement of coordinated sustainable development of the ecological environment and social component of the basin involving impacts of the construction of reservoirs is a major problem that requires urgent attention because of its significance for the development of semi–arid regions in the Loess Plateau (Wang et al., 2016). The findings of the present study are vital for assessing changes in the ecological environment in the region during the last 30 years of the 20th century (Lv et al., 2018). The findings also provide a reference for environmental governance and the prevention of soil erosion in the Qinhe River Basin (Montanari et al., 2013; Jerome, 2000).