Assessing sedimentary records of paleohurricane activity using modeled hurricane climatology

Abstract

[1] Patterns of overwash deposition observed within back-barrier sediment archives can indicate past changes in tropical cyclone activity; however, it is necessary to evaluate the significance of observed trends in the context of the full range of variability under modern climate conditions. Here we present a method for assessing the statistical significance of patterns observed within a sedimentary hurricane-overwash reconstruction. To alleviate restrictions associated with the limited number of historical hurricanes affecting a specific site, we apply a recently published technique for generating a large number of synthetic storms using a coupled ocean-atmosphere hurricane model set to simulate modern climatology. Thousands of overwash records are generated for a site using a random draw of these synthetic hurricanes, a prescribed threshold for overwash, and a specified temporal resolution based on sedimentation rates observed at a particular site. As a test case we apply this Monte Carlo technique to a hurricane-induced overwash reconstruction developed from Laguna Playa Grande (LPG), a coastal lagoon located on the island of Vieques, Puerto Rico in the northeastern Caribbean. Apparent overwash rates in the LPG overwash record are observed to be four times lower between 2500 and 1000 years B.P. when compared to apparent overwash rates during the last 300 years. However, probability distributions based on Monte Carlo simulations indicate that as much as 65% of this drop can be explained by a reduction in the temporal resolution for older sediments due to a decrease in sedimentation rates. Periods of no apparent overwash activity at LPG between 2500 and 3600 years B.P. and 500-1000 years B.P. are exceptionally long and are unlikely to occur (above 99% confidence) under the current climate conditions. In addition, breaks in activity are difficult to produce even when the hurricane model is forced to a constant El Niño state. Results from this study continue to support the interpretation that the western North Atlantic has exhibited significant changes in hurricane climatology over the last 5500 years.Components: 8066 words, 8 figures.

Late Holocene hurricane activity and climate variability in the northeastern Gulf of Mexico

“…Changes in the intensity distribution of hurricanes occurring in concert with changes in storm frequency could cause the frequency of storm deposits in sites with different flooding susceptibilities to diverge. Numerical modeling of late st century hurricane climatology has suggested that declines in overall Atlantic hurricane frequency could occur simultaneously with a broadening of the intensity distribution of hurricanes leading to fewer but more intense storms (Emanuel et al 2008, Gualdi et al 2008, Knutson et al 2008, Zhao et al 2009, Bender et al 2010). …”

“…While advances have been made toward more realistic hurricane intensity distributions in storm climate modeling (Emanuel et al 2008, Bender et al 2010), such models still do not incorporate the feedbacks that tropical cyclones exert on the climate system.…”

Tropical cyclones within the sedimentary record : analyzing overwash deposition from event to millennial timescales

“…Recent compilations of millennial-scale hurricane reconstructions from the western North Atlantic indicate basin wide fluctuations in activity over the last 5000 years Woodruff et al, 2008a). Although these reconstructions are still limited in number, stochastic simulations indicate that observed trends are statistically significant and unlikely to occur under the present climate (Woodruff et al, 2008a).…”

“…In Chapter 4, I apply numerical modeling techniques to assess the statistical significance for trends observed within the paleo-hurricane overwash reconstruction from Vieques (Woodruff et al, 2008a). Results show that breaks in overwash activity occurring from 3600-to-2500 years ago and 1000-to-500 years ago are extremely long and unlikely to occur at the site under the current hurricane climatology and with the present barrier morphology.…”

“…Similar analyses are performed for each of the 29 overwash deposits within the record, and indicate that the flooding magnitude for these events has remained relatively constant through time, with no systematic shifts in intensity attributable to time-varying changes in barrier morphology. This study is the first to inversely model flooding conditions from resultant hurricane-induced deposits, and provides the groundwork for which future studies can expand upon to gain new insight into the overwash process.In Chapter 4, I apply numerical modeling techniques to assess the statistical significance for trends observed within the paleo-hurricane overwash reconstruction from Vieques (Woodruff et al, 2008a). Results show that breaks in overwash activity occurring from 3600-to-2500 years ago and 1000-to-500 years ago are extremely long and unlikely to occur at the site under the current hurricane climatology and with the present barrier morphology.…”