ESH: Response of Extreme Hydrologic Events to Climate Change: Upper Mississippi River

本研究的总体目标是系统地汇编和分析高质量的冲积地层资料，以确定密西西比河上游河谷干流全新世（冰期后）气候变化对陆地水文的响应。具体目标包括：1。1 .定量记录密西西比河上游岛屿大堤和后沼泽环境中与区域全新世气候事件相关的大洪水和极端洪水的重现频率；定量记录与区域全新世气候事件相关的密西西比河上游支流河口淡水环境大洪水和极端洪水的重现频率；, 3。定量记录现代（历史）冲积沉积物中岛屿堤防和后沼泽以及密西西比河上游支流河口淡水环境中大洪水和极端洪水的复发频率。独特的地层档案是可用的，因为密西西比河上游在整个全新世经历了持续的逐渐淤积，在该地区最后一次冰期推进后不久，冰川湖泊的排水造成了晚更新世（晚冰期）冲积物的深沟。从那时起，支流沉积物的再流动逐渐重新填满了密西西比河上游的主要河谷。这里提出的研究是首席研究员长期研究项目的关键组成部分，该项目旨在调查密西西比河上游流域水文地貌对气候变化的反应。然而，我以前的研究主要集中在密西西比河上游的小支流系统上。前期研究表明，5 ~ 200 km2流域小支流的洪水水文和泥沙流动与储存量对即使是很小的气候变化也有强烈的响应。这些变化主要涉及气团和风暴路径边界调整，与年平均气温变化1 ~ 2℃和年平均降水变化不大于10 ~ 20%相关。由于导致小流域（5-200 km2）洪水的物理过程与密西西比河上游流域（10 - 30万km2）洪水的物理过程不一定相同，因此本研究还将研究流域尺度转移如何影响雨、雪融水以及雨雪融水联合洪水对气候变化的敏感性。研究方法包括实地、实验室和定量分析阶段。野外工作的主要组成部分包括从洪泛区冲积地点和支流河口的静水沉积地点提取连续岩心。详细的沉积学和地球化学分析将应用于沉积物岩心，在大多数情况下，采样间隔为1厘米或更短。将进行统计分析，研究历史记录的洪水和气候数据之间的关系，以便与UMR上气候/洪水关系的地质记录进行比较。提出的研究直接有助于提高对陆地地球系统科学的理解，强调水文系统及其如何受到古气候变率的影响。这项研究将提供一个高质量的物理古记录的系统汇编，重点关注气候和极端水文事件之间的联系，特别是涉及大型河流系统的大洪水。拟议研究的结果有望对密西西比河上游极端洪水的强度和复发频率在过去全新世古气候中的表现以及在古气候事件之间的突变期间的表现提供系统的评估。在考虑海洋和大气环流系统“突然翻转”的后果时，这一信息将被证明是非常有用的。

9807715KnoxThe general objective of this research involves the systematic compilation and analysis of high quality alluvial stratigraphic data to determine the terrestrial hydrologic responses to Holocene (post-glacial) climatic changes in the mainstem upper Mississippi River valley. Specific objectives include:1. to quantitatively document recurrence frequencies of large and extreme floods recorded in upper Mississippi River island levee and backswamp environments in association with regional Holocene climatic episodes;2. to quantitatively document recurrence frequencies of large and extreme floods recorded in upper Mississippi River tributary mouth slackwater environments in association with regional Holocene climatic episodes; and,3. to quantitatively document recurrence frequencies of large and extreme floods recorded in modern (historical) alluvial sediments for island levees and backswamps and for tributary mouth slackwater environments of the upper Mississippi River.The unique stratigraphic archive is available because the upper Mississippi River has experienced ongoing gradual aggradation throughout the Holocene following an episode when drainage of glacial lakes at and soon after the last glacial advance in the region caused deep entrenchment of late Pleistocene (late glacial age) alluvium. Since then, remobilization of sediment from tributaries has been gradually refilling the main valley of the upper Mississippi River. The research proposed here is a key component of a long-term research program by the principal investigator to investigate hydrogeomorphic responses to climatic change in the upper Mississippi River valley. My previous research, however, has focused on small tributary systems of the upper Mississippi River. The earlier research showed that flood hydrology and sediment mobility and storage in small tributaries of 5-200 km2 drainage area were strongly responsive to even small climate changes. Those changes typically involved air mass and storm track boundary adjustments that were associated with changes of mean annual temperature of 1-2 C and changes of mean annual precipitation of not greater than 10-20%. Because the physical processes responsible for floods on small watersheds (5-200 km2) are not necessarily the same as for the very large upper Mississippi River watershed (100,000 - 300,000 km2), the present research will also examine how watershed scale transfer affects the sensitivity of rain, snowmelt, and combined rain and snowmelt floods to climate change.The methodology for the research involves field, laboratory, and quantitative analyses phases. The major component of fieldwork involves the extraction of continuous cores from floodplain alluvial sites and from slackwater sedimentary sites in tributary mouths. Detailed sedimentological and geochemical analyses will be applied to sediment cores at sampling intervals of 1 cm or less in most situations. Statistical analyses will be undertaken to study relationships between historically recorded flood and climatic data for comparison with the geologic record of climate/flood relationships on the UMR.The proposed research contributes directly to improved understanding of terrestrial Earth system science emphasizing the hydrologic system and how it has been influenced by paleoclimate variability. The research will provide a systematic compilation of a high quality physical paleorecord that focuses on the linkage between climate and extreme hydrologic events, especially involving large floods on a large river system. Results from the proposed research are expected to provide a systematic evaluation of how magnitudes and recurrence frequencies of extreme floods on the upper Mississippi River behaved within past Holocene paleoclimates and during what appear to be abrupt transitions between paleoclimate episodes. This information should prove quite useful in contemplating the consequences of "abrupt flips" in circulation systems of the ocean and atmosphere.