Abstract: Based on improvement of the distributed hydrology-soil-veg etation model DHSVM and its application to North China,a nested regional climatic-hydrologic model system is developed by connecting DHSVM with RegCM2/China.The simulated climate scenarios,including control and 2×CO2 outputs,are downscaled to 8 stations in Luanhe River and Sanggan River Basins to drive the hydrology model.According to simulation results,under double CO2 conditions,temperature and evapot ranspiration will rise 2.8 and 29 mm,respectively;precipitation also increases but with different values for each basin,6 mm for Luanhe River while 46mm for Sanggan River;runoff change for the two basins is different too,27 mm decrease for Luanhe River Basin while 26 mm increase for Sanggan River Basin.As a result,the runoff in future for Luanhe River Basin and Sang gan River Basin is 74 mm and 71 mm,respectively,which is approximately a quarter of mean annual runoff(284 mm)of the whole country.Total streamf low for the two basins will decrease about 2.5×108m3.All these indicate that the warm and dry trend will continue in the two river basins under double CO2 scenarios.The nested model system,with both climatic and hydrologic prediction ability,could also be applied to other basins in China by parameter adjustment.