Background As an important ecological barrier,the upper Yongding River basin plays a key role for preventing sandstorm and protecting water resources for the downstream where the capital city located.With the impact of climate change and high-intensity human activities,the ecological environment in the basin has undergone significant changes in the past 50 years,and water shortage and water environment deterioration have become increasingly prominent.The impact of climate change and human activities on water quantity and quality is highly related to climate change,basin location and other factors,yet it has obvious spatial heterogeneity.Therefore,revealing the characteristics of regional-scale environmental changes and quantitative and qualitative evolution of water resources and their driving factors is highly needed,which is of great significance for water resources management and water environmental protection in the upper Yongding River basin. Findings(1) The mean temperature of the upper Yongding River basin showed an "abrupt" increasing trend in the past 50 years,and the temperature increased significantly especially after 2000.The magnitude of minimum temperature increase is greater than that of maximum temperature,and the warming trend in winter and spring is higher than that in other seasons.Temperature may have an increase tendency in future.(2) The annual average precipitation in the basin showed a decreasing trend but not statistically significant,while the summer precipitation decreased significantly.The days and the amount of heavy rain and rainstorm showed an extremely significant decreasing trend.Annual precipitation may increase in future.(3) Both the pan evaporation and potential evapotranspiration in the basin have a decreasing tendency,yet not statistically significant.The actual evapotranspiration does not increase with the increase of temperature.(4) The land use change changed dramatically in the basin,with the increase of woodland and construction land and the decrease of cultivated land,unused land and water area as main characteristics.Land use change dynamics are more obvious after 2000 in the basin.(5) Runoff has a significant decreasing trend and water quality is partly polluted in the upper Yongding River basin.High intensity human activity is the main reason for runoff decline and water quality deterioration in the upper Yongding River basin. [WTHZ]Conclusions[WTBZ] (1) The carrying capacity of water resources and water environment are seriously insufficient in the upper Yongding River basin.How to improve the water use efficiency regards to the limited water resources,and how to coordinate the relationship between water resources,ecology and social economic development are highly needed for regional sustainable development and ecological civilization in the upper Yongding River basin.(2) Under the influence of climate change and human activities,the mechanism of water cycle and the process of pollutant migration and transformation will change significantly.How to reveal hydrological cycle and solute migration in the basin under changing environment,and evaluate and predict their effects are hotspots for water security research.(3) Strengthening monitoring,promoting data sharing and improving the models of coupling simulation of water quantity and quality are necessary for water resources research.(4) The upper Yongding River basin has a large drainage area and spans five different provinces.How to plan and promote the comprehensive river basin management is still a key issue which needs to be solved urgently.