Background Yuan River is one of the most important international rivers in Southwest China. Whether the ecological environment of the Yuan River basin is healthy or not has an essential impact on the social and economic development along the coast and the ecological security of other countries in the downstream of the river basin. Therefore, it is of considerable significance to clarify the specific impact of land use/land cover change (LUCC) and climate change on the status of water resources in Yuan River. However, there are few reports on this aspect at present.

Methods The SWAT model was used to quantitatively analyze the effects of LUCC and climate change on basin runoff, and combined with RCP4.5 and RCP8.5 emission scenarios to predict the runoff change of Yuan River basin.

Results 1) SWAT model is suitable for runoff simulation of the Yuan River basin. The model parameter R² and ENS (efficiency coefficient of Nash-Sutcliffe) of the calibration period are 0.63 and 0.62, respectively, and the R² and ENS of the verification period are 0.62 and 0.60, respectively. 2) Extreme land-use scenario simulation shows that the contribution of various land-use types to runoff formation is the strongest in agricultural land, the second in grassland, and the weakest in woodland. 3) The increase of runoff caused by LUCC in Yuan River basin from 2006 to 2015 is due to the transformation of forest land into grassland. The decrease of flow caused by climate change results from both the reduction of precipitation and the increase of temperature, and the reduction of runoff caused by climate change is more significant than that caused by LUCC.

Conclusions 1) Climate change dominates runoff change in the Yuan River basin between 2006 and 2015. 2) Under the two emission scenarios of RCP4.5 and RCP8.5, the runoff reduction rate in the Yuan River basin from 2021 to 2050 is 1.82 times and 2.36 times that of the measured runoff reduction rate from 1971 to 2015, respectively. And the decreasing trend of the RCP8.5 scenario with higher carbon emission is significantly higher than that of the RCP4.5 scene, which is 1.3 times higher than that of the RCP4.5 scenario.