Water security is the basis of sustainable human development. A new evaluation system of water security was established based on the natural–social dualistic water cycle theory, and then applied to characterize water security issues in China. At the national scale, the current state of water security was moderate, which was attributed to the improvement of water resource management level. However, it is still seriously inadequate in coordination of water use between ecological protection and socio-economic development, and wastewater treatment and reuse. Consequently, a resilient and integrated water management with adaptive capacity is needed. Moreover, the water security state in southern China was better than that in northern China, which was mainly attributed to the abundance of water resources in the south. Although the critical factors hindering water security were significantly different among China's 31 administrative regions, the low urban sewage reuse rate was a common factor, and irrigation efficiency was low in most parts of southern China. While in northern China, water resource overexploitation, polluted water quality and degraded aquatic ecosystems were common challenges. The results are consistent with the actual situations of China, and the related analysis can provide a reference for increasing regional water security.

Rock fragments in soil strongly increase the complexity of hydrological processes. Spatial variability of preferential flow and infiltration characteristics, especially along a rocky-mountain hillslope are poorly understood. In this study, five rainfall–dye tracer experiments were performed in the rocky Taihang Mountains, northern China, to investigate the spatial variability of preferential flow and infiltration redistribution on different hillslope positions. Tracers were used to distinguish macropore flow and actual water flow patterns, and preferential flow indices and spatial non–uniformity of the infiltration redistribution were calculated using image analysis. Results showed increasing trends in the dye coverage, maximum infiltration depth, and steady infiltration rate with increased hillslope position, with a preferential flow fraction of 0.10, 0.11, 0.15, 0.29, and 0.26 for the bottom–, down–, mid–, upper–, and top–slope positions, respectively. With increased hillslope position, the spatial non–uniformity of the infiltration redistribution gradually increased in orthogonal and parallel directions to the stained section, and was supported by the fractal dimensions. Positive (gravel mass ratio, saturated water content, altitude, hydraulic conductivity and roots) and negative (bulk density and clay content) impacts on preferential flow and infiltration redistribution were quantitatively emphasized. The characteristic and mechanism of infiltration process were further identified along a rocky-mountain hillslope.