US Gulf Coast tropical cyclone precipitation influenced by volcanism and the North Atlantic subtropical high

Tropical cyclones (TCs) cause significant devastation through storm surge and high winds, but inland flooding from TCP is the leading cause of TC-related fatalities and extensive damage. TCP also triggers cascading hazards such as slope failure, eutrophication, and waterborne pathogen outbreaks. Conversely, TCP is a crucial component of regional hydroclimates, influencing water management, ecosystem services, and drought relief. Climate models predict increased TC precipitation rates due to slower storm translation speeds, warming sea surface temperatures (SSTs), and increased vapor pressure in response to anthropogenic warming. Understanding the full range of TCP variability is essential for assessing future risks. Precipitation and TC variability along the Gulf Coast are influenced by the North Atlantic subtropical high, the North Atlantic Oscillation, and multidecadal sea-surface temperature variability. However, our knowledge is limited by short instrumental records. Paleoclimate proxies can extend our understanding by providing longer-term data on TC activity, intensity, and hazards. While sediment deposits offer records of TC frequency and characteristics, they primarily capture only the most intense storms. Annual-resolution TC reconstructions from speleothems or tree rings are less common and often focus on TC activity rather than TCP. This study aims to address this gap by creating a long-term reconstruction of TCP along the Mississippi Gulf Coast, a region impacted by an average of one TC per year. The study uses a 473-year record to examine multidecadal patterns in Gulf Coast TCP and identify potential climate controls over various timescales.

Several studies have reconstructed pre-industrial extreme TC variability along the Gulf Coast using sediment deposits, providing information on TC frequency and storm characteristics like wind speed and storm surge height. However, these records are often limited by their dependence on coastal geomorphology and hydrodynamic conditions, and primarily capture only the most intense events. Annual-resolution TC reconstructions, typically from isotopic ratios in speleothems or tree rings, are less common. While some studies have employed tree-ring width to estimate TCP in other coastal regions, such reconstructions are limited in spatial coverage and duration. Existing studies focusing on TCP from tree rings predominantly cover North and South Carolina and reconstruct TCP since the 1700s.

The researchers collected longleaf pine samples from various sources in the De Soto National Forest (DNF) in Mississippi, including living trees, remnant stumps, excavated coffins, and a historical house. Dendrochronological analyses were used to cross-date the samples, creating a 473-year chronology extending back to 1540 CE. The adjusted latewood ring width (LWa), showing the strongest correlation with TCP, was used as the predictor in a linear regression model to reconstruct TCP totals. The model captures 40% of the variance in instrumental TCP data and demonstrates temporal stability through split-sample calibration and validation and a Bootstrapped Transfer Function Stability test. The researchers analyzed the relationship between reconstructed TCP and several climate indices. The Bermuda high index (BHI) was used to assess the influence of the North Atlantic subtropical high on TCP, using Spearman's rank correlation. To investigate volcanic influence, a superposed epoch analysis was performed using the Volcanic Explosivity Index (VEI) as a measure of eruption magnitude. To examine multidecadal connections, the reconstruction was compared to an annually-resolved reconstruction of Atlantic multidecadal variability (AMV), and a reconstruction of SST values from the northern Gulf of Mexico was used to investigate the role of the Loop Current.

The 473-year TCP reconstruction reveals significant multidecadal patterns, with distinct periods of low and high TCP totals. The analysis indicates that major Northern Hemisphere volcanic eruptions lead to a significant decline in TCP in the two years following the eruption. This is likely due to reduced storm activity rather than a decrease in precipitation per event. The study also finds a significant, albeit weak, correlation between TCP and the BHI, suggesting an influence of the North Atlantic subtropical high. Over multidecadal timescales, a significant correlation was found between TCP and AMV, with AMV leading TCP by several years. This lagged relationship may be explained by the influence of the Atlantic Warm Pool (AWP) and the Loop Current, which act as conduits between TCs and basin-scale SST variability in the North Atlantic. The northward migration of the Loop Current, representing an expanding AWP, correlates with wet phases on the northern Gulf Coast.

The findings highlight the importance of both short-term (volcanic eruptions) and long-term (AMV, North Atlantic subtropical high) climate controls on TCP variability. The reconstruction extends our understanding of pre-industrial TC variability, providing a unique perspective on the drivers of TCP and extreme events. The connection between volcanic eruptions and TCP decline underscores the role of external forcing mechanisms on TC activity. The weak but significant correlation between AMV and TCP emphasizes the influence of large-scale climate patterns, mediated by regional features such as the AWP and Loop Current. The study's findings contribute to our understanding of the complex interplay between climate variability and TCP, improving flood risk assessment and hydrological predictions. The study emphasizes the need for a more comprehensive network of TCP reconstructions.

This study provides the longest annually-resolved TCP reconstruction to date, offering valuable insights into the multi-scale drivers of TC variability. The findings underscore the influence of volcanic eruptions and the North Atlantic subtropical high on interannual TCP changes, and the weaker but still significant impact of AMV on multidecadal scales. The authors suggest that future research should focus on building a network of TCP reconstructions across the southeastern USA to better characterize regional TC climates, incorporate modeled oceanographic and atmospheric patterns, and improve understanding of past TC-related flood events, particularly in smaller watersheds.

The study's primary limitation is its focus on a single location in southern Mississippi. Although the use of diverse longleaf pine samples expands the temporal coverage, the findings may not fully represent the entire Gulf Coast region. The reconstruction's sensitivity to other precipitation sources aside from TCs is also a consideration; however, this was addressed in the methodology with the inclusion of total precipitation and non-tropical precipitation. The weak correlation between AMV and TCP could be due to the different spatial scales considered. While the AMV reflects North Atlantic SSTs, the reconstruction focuses on TCs near the study site.