There is a sharp decline in runoff and available water resources in North China in recent years. Not only the causes, but also the magnitudes, especially of the dwindling runoff remain largely unclear. Hence the Ye Rive Basin, a typical mountain watershed in North China, is used in this study to determine: (1) the trend of precipitation and runoff via a Mann–Kendall test; (2) the period of drastic runoff decline via a sequential Mann–Kendall test and (3) the driving factors of runoff decline via (i) runoff comparisons for dry and wet years with similar precipitation events, and (ii) regression comparisons on precipitation and runoff for the pre- and post-development periods. Analysis of 40 years (1960–1999) of data shows a significant decline in annual runoff, whereas annual precipitation remains relatively stable. In the basin, runoff decline started in 1974, and became drastic in 1978. Furthermore, runoff analysis for typical dry and wet years, and regression comparisons, indicate that human activity is the main driving factor of runoff decline in the basin. Agricultural water use is the dominant cause of the drastic hydrological changes in the study area.

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