The water resource is insufficient and unevenly distributed in the Yellow River Basin, with great changes in annual and inter-annual runoff. With the impact of climate change and human activities, the strained relation between the supply and demand of water resource in the Yellow River Basin is likely to be further deteriorated. Due to the uncertainties in the climate change impact assessment, current forecasts for the future variation trend of runoff in the Yellow River Basin are inconsistent. This research takes climate change and social-economic developmentas the major driving factors for changes in water resources system of the Yellow River Basin and adopts climate model, hydrological model and scenarios of social-economic development as the main sources of the uncertainties influencing the assessment results. The author improves the simulationaccuracy of climate model and hydrological model through multi-model weighting and improves the reliability of the scenarios of social-economic developmentthrough reasonable forecast of the key development parameters of social-economic development. The author also assesses the impact of climate change and social-economic development on the balance betweenthe supply and demand of water resources in the Yellow River Basin, screens key factors influencing water security in the Yellow River Basin, and proposes applicable countermeasures for future water management in the Yellow River Basin. The main contents and conclusions are as follows:
(1) According to the comparison, which adopts deviations, root mean square errors, simple correlation coefficients and spatial correlation coefficients as the indicators, between the 20C3M outputs of the 8 GCM models downloaded from IPCC Data Center and the measured data from ground meteorological station, MIROC-m is the best model for air temperature simulation and CSIRO30 is a preferable model for the simulation of precipitation. All in all, the outputs of GCM can simulate the air temperature in the Yellow River Basin well, but the outputs are not ideal for the simulation of precipitation.
(2) The multi-objective optimization weighted array of the outputs of different GCMs in the Yellow River Basin by genetic algorithm can simultaneously improve the time and spatial correlation coefficients between simulated and measured data and significantly reduce the root-mean-square error between simulated and measured data, which will effectively improve the time and spatial accuracy of precipitation forecast.
(3) According to the climate change scenarios based on multi-model weighting, the air temperature in the Yellow River Basin will rise significantly in the future. During 2046-2065, the annual average temperatures under scenarios A2 and B1 will be 2.6℃ and 2.4℃ higher than that in the baseline period; during 2081-2100, the figures will be 4.6℃ and 3℃. The precipitation in the Yellow River Basin will also increase in the future. During 2045-2065, the average annual precipitation under scenarios A2 and B1 will be 7.3% and 4.3% higher than that in the baseline period; during 2081-2010, the figures will be 15.7% and 8.1%.
(4) According to the data of precipitation, evaporation and runoff in the Yellow River Basin during 1961-2000, the author calibrates, validates and conducts multi-model weighting on 8 hydrological models. Indicators like Nash-Sutcliffe coefficient, mean square error and water balance are selected to evaluate the performance of the model and the method of weighting. The results shows that genetic algorithm reveals higher hydrological simulation accuracy and stability than various models in both calibration and validation periods, thus it can improve the reliability of hydrological forecasting in the future.
(5) According to hydrological prediction based on multi-model weighting, under scenario A2, the average annual runoff during 2045-2065 and 2081-2100 in the Yellow River Basin is 4.1% and 16.1% higher than that in the baseline period respectively, while the change of the volume of runoff under scenario B1 is not obvious. Under different scenarios, the maximum volume of runoff occurs in August and the minimum occurs in January and February.
(6) The scenario of socio-economic development indicates that,compared to the baseline period,the future demand for water resources in the Yellow River Basin will increase by 2.5%~21.4%. In comparison with the impact of climate change on runoff, socio-economic development has a greater influence on the increase of the demand for water resources. In the future, the contradiction of the imbalance between the supply and demand of water resources in the Yellow River Basin will be more prominent. In order to effectively respond to the impact of climate change and economic development on the water resources system in the Yellow River Basin, we should further strengthen the construction of water-saving capacity and the unified management of water resources.