Climate change has substantial impacts on regional hydrology in the major river basins. To figure out such latent hydrological impacts of changing climate, more reliable hydrological simulations are imperative. In this study, we evaluated the impacts of climate change on hydrological regime in the Upper Yangtze River Basin based on four downscaled and bias-corrected Global Climate Model outputs from Coupled Model Intercomparison Project Phase 5 under four Representative Concentration Pathways (RCP2.6, RCP4.5, RCP6.0, and RCP8.5) driving three hydrological models. Two model evaluation approaches were applied: simple and comprehensive. The comprehensive approach was used to evaluate models in the historical period, optimizing objective function at four gauges, and hydrological models were weighted for impact assessment based on their performance. In such a way, projected streamflow time series are obtained under different emission scenarios. Results show that the annual average discharge is projected to increase by 4.1–10.5% under the RCP scenarios at the end of twenty-first century relative to the reference period (1970–1999). Moreover, the high flow is projected to increase and the low flow to decrease indicating a higher probability of flood and drought occurrence in the basin. The severity of floods and droughts may increase. In comparison with the simple one-site model evaluation approach, the comprehensive method reveals that the anticipated extreme flow events would be less severe, and annual mean discharge slightly lower. The projected results imply that application of the comprehensive model evaluation approach could narrow the simulated spreads of projections significantly, and might provide more credible results.

中文翻译：

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长江上游地区气候变化影响评价水文模型综合评价

气候变化对主要流域的区域水文具有重大影响。为了弄清楚气候变化的这种潜在水文影响，更可靠的水文模拟势在必行。在本研究中，我们基于四个代表性浓度路径（RCP2.6、RCP4）下耦合模型比对项目第 5 阶段的四个缩小和偏差校正的全球气候模型输出，评估了气候变化对长江上游流域水文状况的影响.5、RCP6.0 和 RCP8.5）驱动三个水文模型。应用了两种模型评估方法：简单和全面。采用综合方法对历史时期模型进行评价，优化四个尺度的目标函数，对水文模型进行加权，根据其性能进行影响评估。通过这种方式，可以得到不同排放情景下的预计水流时间序列。结果表明，与参考时期（1970-1999 年）相比，21 世纪末 RCP 情景下的年平均排放量预计将增加 4.1-10.5%。此外，预计高流量会增加，低流量会减少，表明流域发生洪水和干旱的可能性更高。洪水和干旱的严重程度可能会增加。与简单的单点模型评价方法相比，综合方法揭示了预期的极端流量事件的严重程度较低，年平均流量略低。预测结果意味着综合模型评估方法的应用可以显着缩小预测的模拟范围，