Runoff of the 20th and 21st centuries Simulated by CESM1

Global freshwater resources are sensitivity to changes in climate, CO2 concentration and anthropogenic activities. The Community Earth System Model version 1(CESM1) allows simultaneous consideration of the effects of changes in climate, CO2 concentration, anthropogenic nitrogen deposition and land cover on the continental hydrological cycle. Here we evaluate the simulated spatial and temporal pattern for the 20th century global runoff and project the changes for the 21st century under IPCC RCP4.5 scenario from the fully coupled runs of CESM1. The predicted global mean runoff for 20th century increases with a rate of 0.08mm.yr-2, but the trend is not significant. While the upward trend with a rate of 0.30mm.yr-2of global averaged runoff for the 21st century under the RCP4.5 scenario is very significant. The CESM1 can capture the main features of the spatial pattern changes for the 20th century, but tends to overestimate runoff over most parts of the globe( where this could be somewhat accounted for by freshwater consumption). The spatial changes in runoff by the 21st century show a pattern generally consistent with that of 20th century changes, while the areas of increased runoff grow over time from the late twentieth century to the mid twenty-first century.