西南河流源区径流量变化规律及其未来演变趋势

Variation laws and future evolution trends of runoff in the headwaters region of Southwestern rivers

采用统计学方法及集合经验模态分解、小波分析、水文模型等多种方法,在对气象水文、湖泊岩芯、树木年轮、气候模式数据进行深入分析的基础上,研究了西南河流源区径流变化规律与历史丰枯规律及其驱动机制,分析了未来气候变化影响下的径流演变趋势。结果表明:三江源地区的径流近50 a整体表现为上升趋势,雅鲁藏布江流域除尼洋河外的其他区域年径流量整体呈不显著下降趋势,气候变化是导致三江源、雅鲁藏布江和怒江流域径流变化的主要原因,其中降水是引起径流变化最关键的因子;主要河流径流不同时间尺度的丰枯演变规律为,雅鲁藏布江中游全新世洪水事件呈现出早晚全新世频繁、中全新世相对较少的特征,近500 a怒江流域重建径流序列存在10个丰水期和10个枯水期,丰枯序列变化主要受季风环流和厄尔尼诺-南方涛动(ENSO)活动的影响;在未来15~60 a,全球持续增温将使西南河流源区平均年径流深相比近30 a增加6%~14%,而极端径流呈现出“干更干、湿更湿”的变化特征,同时生态因子对径流变化的影响不可忽视。

By using statistical methods, ensemble empirical mode decomposition, wavelet analysis, hydrological models and other methods, the laws and driving mechanisms of runoff changes, historical floods and droughts, and the trend of runoff changes under the impact of future climate changes in the headwaters region of the southwestern rivers were investigated on the basis of in-depth analysis on meteorological and hydrological data, lake cores data, tree rings data, and climate model prediction data in this study. The results showed that the annual streamflow in the Three-River Headwaters region showed a significant upward tendency during the past 50 years, and the annual streamflow in the Yarlung Zangbo River basin showed an insignificant downward trend except the Niyang River basin. Climate change was the major factors to affect the streamflow changes in the Three-River Headwaters region, Yarlung Zangbo River basin and Nujiang River basin, and precipitation played the most important role for these changes. Results indicated that the variations between wet and dry periods are different in these rivers. In the mid reach of the Yarlung Zangbo River, flood events in wet periods frequently occurred in the early and late Holocene, but relatively less occurred in the Mid Holocene. The reconstruction runoff time series of the Nujiang River basin over the past 500 years includes 10 wet periods and 10 dry periods. The variations between wet and dry periods in the region are mainly controlled by the monsoon circulation and ENSO activities. The continued global warming in the next 15—60 years will increase the average annual runoff of the Southwestern rivers by 6%—14% compared with the past 30 years. Meanwhile, the extreme runoff presents the characteristics of “drier and drier, wetter and wetter” and ecological factors have a non-negligible effect on runoff changes in the future.