2万年以来黄河下游季风演变及洪水与河道变迁机制研究

As a country deeply influenced by the East Asian monsoon, a large number of abnormal weather events and related disasters are resulted from the monsoon variability in China. The Lower Yellow River is one of the areas most frequently influenced by flood disasters. According to historical documents, the floods in Henan and Shandong Provinces are about 160 and 106 times, respectively from 1766 BC to 1900 AD. And the recorded river course change and migration occurred as many as 26 times in the Lower Yellow River before the liberation. After the founding of New China in 1949, the people’s government has allocated enormous manpower, financial resources, and materials to implement soil and water conservation in the middle, reinforce levees in the lower and build hydraulic engineering in the trunk stream (such as Sanmenxia Dam, Xiaolangdi Dam, etc), which has ensured river-safety of 50 years in the lower reaches of the Yellow River. But with frequent occurrences of extreme weather events (abnormal monsoon rainfall, El Nino, etc) caused by global climate change, the flooding in the lower reaches of Yellow River will be extremely severe. Embankment safety and channel changes are increasingly threatening human livelihood and property on both sides along the Yellow River. So, how to bring the Yellow River under control is a very important scientific problem for officials and scientists. For its continuous deposition, high resolution, and rich information, Lake sediment is an important natural archive and it has successfully been used to study past environmental changes. It has vital significance for regulation and researches of reserved flow course of the Yellow River to identify and restore the ancient monsoon information and estimate the future climate and especially the possibility of heavy monsoon rains from lake sedimentary record. Based on high-resolution extraction of monsoon evolution and channel changes recorded by palaeo-lake sediments in Daluze Lake, Juyeze Lake, and Haiyusou Lake located in the Lower Yellow River, this study attempt to (1) establish a sequence of the monsoon rainfall and flooding since 20, 000 years BP from the Lower Yellow River area; (2) reveal the natural probability of channel changes and spatial characteristics; (3) analyze the hydrology cycle and wet-dry transition status under the monsoon variation; and (4) explore the process and mechanism of monsoon floods on channel changes of the Yellow River in the stages of the last glacial maximum, late glacial, early holocene, middle and late holocene. The overarching objective of this proposed study is to provide a scientific basis for flood control and sustainable development of the lower Yellow River area.

季风变化是导致黄河下游洪涝灾害的关键因子，也是引发黄河河道变迁的重要气候因素，而黄河下游洪泛区发育的一系列湖泊记录了黄河的演化历史。本项目拟通过对黄河下游大陆泽、大野泽、海隅薮等古湖沉积物中高分辨率的洪水、季风演变和河道变迁信息记录的提取，建立2万年以来黄河下游洪水和季风降雨演变序列，揭示河道变迁的自然概率和时空变化特征，特别是揭示末次盛冰期、晚冰期和全新世早、中、晚期季风变化、洪水和河道决口变迁的时空变化规律，分析季风变异下的水文循环与干湿变迁状况，探讨季风暴雨洪水对河道变迁的影响过程与机理，以为黄河治理及防洪减灾与可持续发展提供科学依据。

季风降水是区域气候和自然环境形成的基础，季风波动演变对区域水文循环和旱涝灾害以及植被与生态变迁具有深刻影响。黄河下游地区是我国深受季风降水变异引发的洪涝灾害最频繁的一个地区。随着全球气候异常以及黄河下游水沙形势的巨大变化，黄河下游洪涝形势异常严峻。理解历史时期黄河下游地区环境演变及其规律是治理黄河的重要科学基础。本课题主要针对2万年来黄河下游地区气候、洪水、河道变迁等问题，以湖泊沉积物为主要研究材料，进行了黄河下游地区环境演化序列、气候环境事件识别与规律、河道变迁及季风降雨、洪水与河道变迁之间的关系机理等研究。获得了大陆泽（50m长岩芯柱2根）、宁晋泊（15m长岩芯柱2根）、海隅薮（50m、30m、20m、20m岩芯柱四根）等古湖高质量的湖泊沉积岩芯。测定了沉积物年代，分析了粒度、磁化率、元素、孢粉等环境指标。初步建立了年代序列和环境演化序列。.基于年代数据和环境指标，取得的重要成果如下：1、首次揭示了黄河下游地区晚全新世淡水碳库效应的变化特征，提出了用溶解无机碳（稳定与放射性碳）同位素反演地表水循环的新思路。2、黄河下游地区古湖盈缩迁徙是气候变化和黄河泛滥改道共同作用的结果，其中黄河洪水和泛滥改道是主因。3、末次盛冰期以来黄河下游地区环境演化主要受控于太阳辐射的变化，其中H事件、YD事件和8.2Ka事件等气候突变事件主要与复杂的地球系统内部动力学过程有关。此外，通过黄河下游地区湖泊现代沉积物的研究，揭示了总磷、水深和硫酸盐对沉积物摇蚊亚化石空间分布的影响。碳库效应变化特征的研究对修正黄河下游地区湖泊沉积物年代具有重要参考价值，黄河下游地区气候演变、洪水泛滥、河道变迁及其与湖泊盈缩关系的研究有助于深刻理解黄淮海平原河湖关系，对该区国土规划、江河治理、防洪减灾、水利工程建设和水资源开发调度以及生态文明建设等具有十分重要的现实意义。