As an important soil and water conservation engineering measure, check dams have been constructed on a large scale in the Loess Plateau of China. However, their effects on runoff and sediment processes in the basin are still unclear. In this study, the hydrodynamic processes of the Wangmaogou watershed located in the Loess Plateau were simulated, and the influence of check dams on the flood and erosion dynamic processes in this watershed were also evaluated. The results showed that the check dams obviously reduced the flood peak and flood volume and mitigated the flood process. After the dam system was completed, the flood peak and flood volume were reduced by 65.34% and 58.67%, respectively. The erosion dynamic distribution of the main channel in the small watershed was changed to different extents by the different dam type combinations, and the erosion dynamic parameters of the channel decreased most after the dam system was completed, when the velocity and runoff shear stress of the outlet section were reduced by 10.69% and 31.08%, respectively. Additionally, the benefits of sediment reduction were most obvious after the check dam system was completed, with the sediment discharge in the watershed being reduced by 83.92%. The results of this study would provide specific implications for construction and management of check dams in the Loess plateau.

Baseflow is a critical component of streamflow in arid areas. Determining variations in baseflow and the factors affecting it have positive roles for water resource utilization in arid watersheds. Two watersheds, the Hailiutu River watershed (HLTR) and the Dali River watershed (DLR), located in two different geomorphological regions of the middle Yellow River, were selected for this study. By using the Eckhardt segment method (fourth digital filtering method, DF4), baseflow was separated from streamflow based on its daily data. Mann-Kendall trend test analysis (M-K trend test) was used to test the trends in baseflow change at different times. Complex Morlet wavelet analysis was used to judge baseflow periodicity. Heuristic segmentation and sequential cluster analysis were used to identify the potential change points in the baseflow series for the two regions together with Pearson correlation coefficient. The results showed: (1) the annual baseflow of the HLTR and the DLR showed significantly decreasing trends (P < 0.01), more significantly for the HLTR (0.33 × 10⁸ m³) than the DLR (0.20 × 10⁸ m³). The annual base flow index (BFI, baseflow/total streamflow) in the wind-sand region (0.75) was larger than for the loess region (0.55), and the BFI in the wind-sand region was more stable in different periods. (2) The annual baseflow of the HLTR and the DLR both exhibited a complete main cycle of 42 years and 38 years, respectively. The change points of the annual baseflow in the HLTR were 1967 and 1986, and 1971 and 1996 in the DLR. (3) There was no significant change in annual precipitation in the two watersheds, while annual reference evapotranspiration (ET₀) in the DLR showed a significant increasing trend (P < 0.01). The normalized difference vegetation index (NDVI) on the DLR (0.40) was higher than on the HLTR (0.26). (4) Baseflow in the wind-sand region, where vegetation improvement was the only ecological activity, decreased faster than in the loess region where there had been numerous ecological measures such as vegetation improvement, check dams and terraces. This implied that comprehensive measures such as these were helpful in slowing the rate at which the baseflow decreases. Therefore, the effect of ecological construction should be considered in future baseflow studies in other geomorphological types within the Middle Yellow River Basin.

In the context of “carbon peak, carbon neutrality”, it is important to explore the spatial correlation network of carbon emission efficiency in the construction industry and its formation mechanism to promote regional synergistic carbon emission reduction. This paper analyzes the spatial correlation network of carbon emission efficiency in China’s construction industry and its formation mechanism through the use of the global super-efficiency EBM model, social network analysis, and QAP model. The results show that (1) the national construction industry’s overall carbon emission efficiency is steadily increasing, with a spatial distribution pattern of “high in the east and low in the west”. (2) The spatial correlation network shows a “core edge” pattern. Provinces such as Jiangsu, Zhejiang, Shanghai, Tianjin, and Shandong are at the center of the network of carbon emission efficiency in the construction industry, playing the role of “intermediary” and “bridge”. At the same time, the spatial correlation network is divided into four plates: “bidirectional spillover plate”, “main inflow plate”, “main outflow plate”, and “agent plate”. (3) Geographical proximity, regional economic differences, and urbanization differences have significant positive effects on the formation of a spatial correlation network. At the same time, the industrial agglomeration gap has a significant negative impact on the formation of such a network, while energy-saving technology level and labor productivity differences do not show any significant effect.