Streamflow components (surface runoff and baseflow) play distinct regulatory roles in global water cycles and ecosystem stability; however, systematic understanding of their differential responses to climate change remains limited. This study developed a two-stage runoff model based on the generalized proportionality hypothesis. Using the trend-preserving bias-corrected climate data from five regional climate models under RCP4.5 and RCP8.5 scenarios, we systematically projected streamflow component responses across 56 hydrological stations nested in 13 basins of China's Loess Plateau during 2021-2050. Model validation demonstrated satisfactory performance (R2 = 0.898 and 0.902 for surface runoff and baseflow, respectively), compared with the observed data. Under RCP4.5, increased precipitation (ranging from 5.7 mm/10a to 46.3 mm/10a) raised surface runoff at 95 % of stations and baseflow at 80 % of stations. Under RCP8.5, enhanced evapotranspiration (ranging from 13.6 to 18.8 mm/10a) significantly reduced baseflow at 30 % of stations, far exceeding the 11 % for surface runoff. This differential response originated from inherent hydrological characteristics: rapid surface runoff generation triggered by storm rainfall, and slow soil water-to-groundwater transformation processes. The model provides a novel analytical framework for coupled streamflow component assessment and adaptive water resource management under changing environments.