Abstract

Hydroclimate variability plays a central role in shaping ecosystems, agricultural productivity, and water security, yet its response to anthropogenic forcing remains uncertain. Facing growing risks from floods, droughts, and shifts in circulation patterns, our ability to anticipate and diagnose hydroclimate change has become a critical scientific priority. However, the instrumental record is too short to capture the full range of natural variability, and models often diverge in their projections of water cycle change in many regions of the world. Observations, proxies, and modeling of stable O and H isotope ratios in water (hereafter, “water isotopes”) offer a unique opportunity to address these gaps, as they integrate signals of temperature, precipitation, circulation, and moisture transport at local to global scales, and geologic archives preserve these signals on timescales that extend beyond the instrumental period. This dissertation employs novel approaches to intercomparing water isotope proxy data and isotope-enabled climate model simulations to examine hydroclimate variability from the start of the Last Millennium (1000 C.E.) through the industrial era, and into the future. First, I perform a synthesis of isotope-based proxy records to evaluate the far-reaching hydroclimate impacts of major features of the climate system like the North Atlantic Oscillation (NAO) and compare these results with model simulations. I find stronger multidecadal variability in the NAO than is captured by models, highlighting that models may not capture the full range of low-frequency dynamics in future projections. I then use a novel approach to detecting change points in spatiotemporally incomplete time series to identify the timing of industrial-era hydroclimate transitions which are often obscured by natural variability. This analysis of globally distributed proxy records is the first systematic evaluation of the timing of global hydroclimate shifts across the industrial transition. Tropical and monsoon-sensitive records identify a reorganization of hydroclimate around the onset of industrial forcing but preceding the onset of global mean warming. The spatial pattern of these changes implicates reorganizations of tropical circulation as drivers of globally coherent isotopic trends. These results indicate that tropical ocean-atmosphere interactions play a central role in mediating the sensitivity of the water cycle to anthropogenic forcing. Finally, I explore the combined impacts of anthropogenic warming and large-scale atmospheric dynamics on the hydrologic cycle in experiments of future warming. I use an isotope-enabled projection of 21st century climate under high greenhouse gas forcing to demonstrate that, despite a weakening of the Pacific and Indian Ocean Walker Circulation, thermodynamic changes in atmospheric water vapor drive a greater reliance on remote moisture sources across the tropical oceans. By bridging proxy evidence, modern observations, and isotope-enabled modeling, this dissertation advances understanding of the mechanisms governing hydroclimate variability across inter-annual to centennial timescales. The findings highlight the value of applying novel methodological approaches to leveraging the information contained in water isotope proxy and observational data, applying these lessons to improve the fidelity of climate models, sharpen estimates of regional rainfall change, and inform water resource planning and risk assessment in a warming world.

Committee Chair

Bronwen Konecky

Committee Members

Alexander Bradley; Brent Williams; David Fike; Roger Michaelides

Degree

Doctor of Philosophy (PhD)

Author's Department

Earth & Planetary Sciences

Author's School

Graduate School of Arts and Sciences

Document Type

Dissertation

Date of Award

12-17-2025

Language

English (en)

Author's ORCID

0009-0009-0160-9858

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Available for download on Thursday, December 16, 2027

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