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

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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.