Natural Drought and Flood Histories from Lacustrine Archives Active

Statement of Problem: Heavy rainfall, flooding, and drought frequently devastate North American populations and are predicted to continue posing serious threats over the next century.  These hydrologic extremes and regional hydrology at centennial and millennial timescales are not well understood. Paleoclimate records capture this low-frequency variability that instrumental records are too short to capture, yet the hydrology of the central U.S. is highly complex and paleorecords from the region are exceedingly sparse. 

This project aims to expand existing data with additional paleorecords, which are needed to disentangle the complex patterns of and controls on interior continental hydrologic variability during the past ~12,000 years (i.e. the Holocene).  Clarifying the spatial patterns of drought and moisture trends is fundamental for comparison with other datasets to understand the mechanisms that drive natural, low-frequency variability and for improving computer models that predict future changes.  Data produced for this project is directly useful for local, state, and federal governments for mitigation planning, disaster relief, wildlife conservation, and resource management.  Climate model researchers will benefit from data produced during this project, which provides an independent dataset to test model performance and improve prediction of future patterns and trends. 

Why this Research is Important: This project performs research that is vital to guiding decision-making and policy for preserving our nation’s resources, specifically water resources and wildlife habitat.  By characterizing the history and controls of drought across the landscape, this project assists in the management of the water resources that are vital for drinking water supplies, agriculture, and industry. This project advances understanding of the drivers of change and improves predictability of natural hazards, including floods and tropical cyclones, that threaten the safety and economic prosperity of the nation’s populations. 

Objective(s):

• Develop paleorecords from the North American continent and surrounding landmasses, focusing on regions with substantial spatial gaps and/or complex spatial patterns of paleohydrologic extremes.
• Determine the natural, baseline variability of floods and droughts to assist resource managers, improve computer models, and improve natural disaster mitigation.
• Synthesize paleorecords to explain spatial patterns of paleohydrologic extremes across the North American continent and better understand the mechanisms of change during the Holocene.

Sources/Usage: Public Domain.

Methods: Preliminary study site research will include searching the literature for previous work performed in the region, searching online databases for site information and data from previous studies, using historic maps and imagery to characterize the quality of proposed sites for flood and lake level reconstructions, and performing site visits to obtain basic water depth and geophysical (e.g. ground penetrating radar/seismic reflection) data as well as water and surface sediment samples.  Sites determined to have high potential for archiving a continuous, high-resolution record of environmental changes with known historical flooding/drought will be prioritized to improve proxy validation.

Sediment cores will be split and imaged with classic sedimentology observations described in detail.  Sediment sub-samples will be analyzed for bulk mineralogy, grain size, and organic content.  These basic analyses will guide more specialized lab measurements for each site based on the presence and variability in abundance/types of geochemical, geophysical, and/or biological sediment components downcore.  Sediment-based records will be dated using radiometric dating techniques (e.g. radiocarbon), and statistical age modeling will be performed to produce age-depth relationships with uncertainty approximations.

Interpretations of flood histories will be based upon multi-proxy evidence for high energy event deposition (e.g. coarse grain abundance, stratigraphic evidence for event deposition and/or slumping, geochemical evidence of sediment delivery from land surrounding the lake during periods of higher runoff) paired with elevation-based flood modeling, where possible. Where the sediment record overlaps with instrumental data, proxy validation will be performed to strengthen downcore proxy interpretations.

Interpretations of drought histories will be based upon multiproxy evidence, mainly proxies for lake salinity, runoff, stratigraphic evidence for desiccation, and lake water elevation changes.  Supporting information from vegetation proxies, diatom assemblages, evidence of fires, and isotopes of precipitation will be included when possible.  Where the sediment record overlaps with instrumental data, proxy validation will be performed to strengthen downcore proxy interpretations.