ABSTRACT

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
Warming temperatures associated with global climate change are expected to lead to more frequent and intense droughts in many mid-latitude regions. Understanding spatial patterns, magnitudes, and frequencies of past decadal-to-multidecadal droughts, and linkages of these patterns to dynamics of the coupled ocean-atmosphere system, is critical to assessing mechanisms and providing the foundation for risk assessment and prediction. There is a clear need for records of past hydroclimate variability in humid regions, where tree-ring based reconstructions lack hydroclimate sensitivity and/or temporal depth. This research produces a network of peatland-derived hydroclimate records spanning the past 3000 years in humid regions of North America. The network is used in conjunction with the tree-ring record of semi-arid regions and other drought-sensitive records to determine continental-scale footprints of past moisture anomalies. High-resolution analyses of testate amoebae, peat humification, and plant macrofossils provide detailed perspectives on hydroclimate variability. High-precision chronologies during significant mid-latitude drought episodes, particularly the Medieval Climate Anomaly (MCA), provide robust portrayals of moisture anomalies during these critical events. Data generation and synthesis is coupled with analyses of instrumental records of drought, precipitation, and sea-surface temperatures (SSTs) to test the hypothesis that widespread droughts like those during the MCA represented an amplification or unusual persistence of an observed mode of 20th century hydroclimate variability. Data-model comparisons and modeling experiments, constrained by proxy SST records, are used to assess the relative importance of Atlantic and Pacific Ocean influences on North American hydroclimate and the potential dynamic response of the climate system to changes in external forcing. The research provides spatial and temporal reconstructions of multidecadal hydroclimate variability in understudied regions, linking this variability to dynamics of the ocean-atmosphere system through synthesis of observational and modeling results, and identifying mechanisms and dynamics of the largest droughts to affect the North American continent in the last 3000 years. This work documents late Holocene droughts in regions conventionally assumed to have low drought risks, potentially transforming both scientific and societal perceptions.
Results are disseminated through public lectures, a web site, teaching and advising at the University level, and organizational networks. Data is distributed through the NOAA paleoclimatology program, as well as other outlets. The project includes interdisciplinary training of graduate students and research experience for numerous undergraduates. The PI has a strong track record of recruitment of women. The PI incorporates project activities into course materials and seminars. The project renews a productive collaboration between the PI and the University of Wisconsin's CCR, taking advantage of the wealth of data created by the first mid-Holocene-to-present transient run of a fully coupled ocean-atmosphere-land model.

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