Date: November 2, 2023
Location: OCNPS 200

The Ocean & Earth Sciences departmental seminar informs students, staff, faculty, and the University community about recent issues. Please join us for a reception in OCNPS 404 after the seminar.

Speaker: Josh Bregy, Clemson University,                   

Host: Wallace


Paleo-Perspectives on Hydroclimatic Variability and Extremes in the Southeast US: the Role of Tropical Cyclones and the Bermuda High

Climate projections suggest that tropical cyclone precipitation (TCP) rates could increase in response to greenhouse forcing. However, consistent trends in TCP have yet to be identified. While satellites and stations are important data sources, the short record length or irregular distribution limits our understanding of TCP and its regional climatic drivers. To address this, we developed a high-resolution, gridded (0.25°x0.25°) TCP product across the eastern United States (1948–2015 CE). We use this dataset to characterize the spatial patterns of TCP, showing that it is highest along the Gulf and Mid-Atlantic coasts, which receive a greater proportion of seasonal rainfall from TCs. Furthermore, we identify connections between TCP patterns and the western flank of the North Atlantic subtropical high (NASH), which steers storm tracks. This instrumental dataset is then used to calibrate a reconstruction model representing the relationship between TCP and latewood width in longleaf pine (Pinus palustris, Mill.). We use this model to reconstruct nearly 500 years of seasonal TCP totals (1540–2012 CE) along the northern Gulf Coast, capturing distinct multidecadal patterns in mean TCP and the frequency of years with TCP totals ³75th percentile. Changes in TCP are shown to respond to explosive volcanism and western flank position, declining after an eruption or when the flank is farther west. Finally, given the connection between TCP and the NASH, we reconstructed an index of the western flank (Bermuda High Index, or BHI) over the Southeast (1140–2009 CE) using a tree-ring network from the Southeast US. In our reconstruction, we document a significant increase in flank variability starting in the 20th century, which co-occurs with negative trends in the BHI at lower quantiles. These suggest an increase in the frequency and extent of westward migrations of the western flank. Consequently, regional precipitation patterns are likely to exhibit greater variability given that we document a strong connection between flank position and regional moisture. Finally, we note that explosive tropical eruptions can cause prolonged shifts in flank position, with the flank shifting west and widespread drying occurring in the four years following an eruption. Ultimately, our reconstructions provide critical insight into characterizing the patterns and regional drivers of hydroclimatic extremes, potentially mitigating hazard risks in a region vulnerable to the effects of climate change.