This study investigates the projected changes in runoff (R), precipitation (P), evapotranspiration (ET), and soil moisture (SM) based on the fifth and sixth phases of the Coupled Model Intercomparison Project (CMIP5 and CMIP6) and quantifies the uncertainties associated with these changes on annual and seasonal scales. The results indicate that all four hydrological variables show an increase over most of the global land surface under a high emissions scenario (SSP5-8.5) during the period 2080–99 relative to 1970–99. Specifically, 72%, 81%, 82%, and 66% of the global land area, respectively, show increased annual runoff, precipitation, ET, and SM. The uncertainties in CMIP6 are dominated by model uncertainty (76% for R, 73% for P, 89% for ET, and 95% for SM) during the twenty-first century, with internal variability decreasing over time and scenario uncertainty increasing. The low-latitude regions exhibit the highest uncertainty in hydrological projections. In CMIP6, the uncertainty of projected changes in precipitation contributes the most to the uncertainty of projected changes in runoff, followed by ET and SM. Overall, the performance of CMIP5 and CMIP6 models is similar in terms of hydrological changes and the composition of their uncertainties. This study provides a theoretical reference for improving the hydrological components in global climate models to enhance the reliability of future hydrological projections.This study investigates the projected changes in runoff (R), precipitation (P), evapotranspiration (ET), and soil moisture (SM) based on the fifth and sixth phases of the Coupled Model Intercomparison Project (CMIP5 and CMIP6) and quantifies the uncertainties associated with these changes on annual and seasonal scales. The results indicate that all four hydrological variables show an increase over most of the global land surface under a high emissions scenario (SSP5-8.5) during the period 2080–99 relative to 1970–99. Specifically, 72%, 81%, 82%, and 66% of the global land area, respectively, show increased annual runoff, precipitation, ET, and SM. The uncertainties in CMIP6 are dominated by model uncertainty (76% for R, 73% for P, 89% for ET, and 95% for SM) during the twenty-first century, with internal variability decreasing over time and scenario uncertainty increasing. The low-latitude regions exhibit the highest uncertainty in hydrological projections. In CMIP6, the uncertainty of projected changes in precipitation contributes the most to the uncertainty of projected changes in runoff, followed by ET and SM. Overall, the performance of CMIP5 and CMIP6 models is similar in terms of hydrological changes and the composition of their uncertainties. This study provides a theoretical reference for improving the hydrological components in global climate models to enhance the reliability of future hydrological projections.