Abstract: The water retention functions in the source region of the Yellow River play a vital role in water resource security and ecological protection in the lower reaches of the Yellow River. The research on the spatiotemporal variations of water retention functions and their influencing factors in the source region of the Yellow River is conducive to the ecological protection and high-quality development of the basin. Based on the meteorological and hydrological data of the source region of the Yellow River from 1957 to 2016, we estimated the change trend and mutation time of meteorological and hydrological factors by Mann-Kendall test and Pettitt mutation analysis method, and examined the contribution of climate change and human activities to runoff variation using hydrological simulation attribution method. Further, we applied the WEP-L model to estimate the spatial and temporal variations of the amount of water retention and various water retention functions in the source region of the Yellow River, and comprehensively analyzed the influence of different factors on the water retention functions. The results showed that temperature significantly increased from 1957 to 2016. According to the mutation time of the runoff, the runoff sequence was divided into the base period (1956-1989) and the change period (1990-2016). The contribution of climate change and human activities (land use change) to the decrease of runoff during the change period was 32% and 68%, respectively. The amount of water retention showed a non-significant increasing trend from 1957 to 2016, with a rate of 0.36 mm·a^-1. The amount of water retention in the northern and western regions increased during the change period, while it decreased in the southern and southeastern parts of the study area. Among the functions of water retention, the functions of maintaining vegetation water use, replenishing basic flows, and reducing floods showed an increasing trend over the years, but the function of replenishing basic flows weakened in the southeast region during the change period. Precipitation was the main factor affecting the variation of water retention functions, while temperature indirectly affected the water retention functions by changing the underlying surface conditions.

Key words: water retention function, WEP-L model, attribution analysis, climate change, source region of Yellow River