Research

Increasing precision in extreme precipitation assessment

This manuscript was published in Journal of Climate in February 2025 and highlights a blend of rainfall observations and climate modeling that I used to re-evaluate an extreme storm that caused widespread flooding in St. Louis, MO and eastern Kentucky in July 2022. My method improved the precision of estimating extreme precipitation from these types of storms by 24 - 94%. I showed that the storm in 2022, which was previously declared a "1-in-1,000-year rain event", was approximately a 1-in-500-year event in St. Louis, MO and a 1-in-300-year event in Kentucky. My assessment demonstrated that a storm like the one in 2022 is about two to four times more likely to occur now when compared to the 1,000 years prior to the industrial era.

Central American hydroclimate change during the Last Glacial Maximum

As a part of my postdoctoral work, I am utilizing water isotope- and water tracer-enabled simulations of iCESM1 to quantify changes in rainfall and the isotopic composition of rainfall and how these are impacted by glacial extent, greenhouse gas concentrations, and sea level changes during the Last Glacial Maximum (~21,000 years ago). With the water tracer results, we can determine changes in moisture source and delivery to Central America from 40 different terrestrial and marine regions across the globe (shown below).

Extreme northward displacement of West African monsoon rainfall

I am presently in the planning stages of a project that will use several climate datasets (CESM1 Preindustrial and paleoclimate runs, reanalysis data) to assess the atmospheric patterns associated with years when West African monsoon rainfall reaches extreme northerly limits. I plan to utilize machine learning and data science applications to pinpoint the most likely variables and spatial patterns associated with years of simulated northerly extremes (blue seasonal cycle lines in plot below).

"Northern Hemisphere vegetation change drives a Holocene thermal maximum" published in Science Advances!

Abstract: The Holocene thermal maximum, a period of global warmth evident in early to mid-Holocene proxy reconstructions, is controversial. Most model simulations of the Holocene have not reproduced this warming, leading to a disagreement known as the Holocene Temperature Conundrum. Pollen records document the expansion of vegetation in the early and mid-Holocene African Sahara and Northern Hemisphere mid- and high latitudes, which has been overlooked in previous modeling studies. Here, we use time slice simulations of the Community Earth System Model to assess the impact of Northern Hemisphere vegetation change on Holocene annual mean temperatures. Our simulations indicate that expansion of Northern Hemisphere vegetation 9000 and 6000 years ago warms Earth’s surface by ~0.8° and 0.7°C, respectively, producing a better match with proxy-based reconstructions. Our results suggest that vegetation change is critical for modeling Holocene temperature evolution and highlight its role in driving a mid-Holocene temperature maximum.

View the publication here: https://www.science.org/doi/10.1126/sciadv.abj6535

Adapted from Thompson et al. (2019). GRL.

Dissertation Title: "Modeling the Regional and Global Climate Responses to Holocene Land Surface Change"

My dissertation, which was successfully defended in June 2021, is a compilation of four content chapters that each investigate the climate response to Northern Hemisphere land surface change during the Holocene.

Abstract:

Widespread land surface changes took place in the Northern Hemisphere throughout the Holocene epoch (11,700 years ago to the present). The most notable of these changes were large increases in vegetation cover that occurred throughout the African Sahara. Yet, the varied responses of regional and global climate to this land surface change are not well understood because few modeling studies have directly incorporated it in their experiments. This dissertation presents new Earth system modeling results that include land surface changes in the African Sahara and Northern Hemisphere mid- and high latitudes to directly identify the responses of regional and global climate to these changes. The chapters in this dissertation provide various resolutions to several challenges in reconciling Holocene model and proxy reconstructions of both hydroclimate and temperature.

Chapters 2 and 3 investigate challenges related to the impact of African Saharan greening, known as the “Green Sahara”, on the West African monsoon during the mid-Holocene. Conclusions from these chapters better constrain the mid-Holocene response of African hydroclimate to a wide array of land surface processes associated with the Green Sahara. Chapter 2 explores the competing impacts of the direct radiative and indirect aerosol-cloud effects associated with the vegetation-induced reduction in dust aerosols, providing an improved understanding of the West African monsoon response to vegetation and dust forcing in the mid-Holocene. Chapter 3 examines how vegetation-induced changes in the isotopic composition of precipitation and soil water help to constrain estimates of the monsoon’s northernmost limit. By showcasing a previously unknown positive anomaly in the isotopic composition of precipitation, this chapter suggests a mid-Holocene northernmost limit of ~23–28°N for the West African monsoon.

Chapters 4 and 5 expand the spatial and temporal scope of this dissertation and investigate external climate responses, both regional and global, to Holocene land surface change. Both of these chapters offer increased Northern Hemisphere vegetation as a resolution to challenges related to reconstructing Holocene climate with model simulations and geochemical proxies. Chapter 4 explores the opposing isotopic signature of the North American monsoon in comparison with other Northern Hemisphere land monsoons and shows that the Green Sahara is likely responsible for this opposing behavior by modulating the local Walker circulation. Seasonal exploration of hydroclimatic and stable water isotopic changes elucidates the factors contributing to the evolution of the North American monsoon. Chapter 5 investigates the controversial model-data disagreement in reconstruction of Holocene global temperatures known as the Holocene Temperature Conundrum. By inclusion of Holocene increases in vegetation in the African Sahara and Northern Hemisphere mid- and high latitudes, the results of this chapter suggest that vegetation change drives a mid-Holocene maximum in annual global mean temperatures and better aligns model simulations with proxy data.

Taken together, findings from this dissertation highlight the importance of vegetation in driving past climate change and in reconciling results from model simulations with geochemical proxy data.

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