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Topic

Explaining spatial adjustments in the global atmospheric water cycle under multiple climate forcings

School of Earth and Ocean Sciences

Date & location

• Thursday, December 19, 2024
• 9:00 A.M.
• Clearihue Building, Room B017

Examining Committee

Supervisory Committee

• Dr. Adam Monahan, School of Earth and Ocean Sciences, University of Victoria (Supervisor)
• Dr. Alex Cannon, School of Earth and Ocean Sciences, UVic (Member)
• Dr. Nathan Gillett, School of Earth and Ocean Sciences, UVic (Member)
• Dr. Tara Troy, Department of Civil Engineering, UVic (Outside Member)
• Dr. Adriana Raudzens Bailey, Department of Climate and Space Sciences and Engineering, University of Michigan (Outside Member)

External Examiner

• Dr. Daniel McCoy, Department of Atmospheric Science, University of Wyoming

Chair of Oral Examination

• Dr. Sarah Dudas, Department of Biology, UVic

Abstract

This dissertation examines the response of the global atmospheric water cycle to various climate forcings, with a focus on understanding how and why spatial patterns of the water cycle adjust. Through a combination of model experiments and theoretical analysis, this research identifies key mechanisms driving the spatial redistribution of water cycle attributes in a changing climate. The findings are presented in three core chapters.

The first chapter investigates the impact of variability in aerosol emissions, particularly from biomass burning, on the global hydrologic cycle. Using Earth System Model simulations, the study shows that increased variability in biomass burning emissions amplifies evaporation, atmospheric moisture, and precipitation. Regional factors, such as ocean heat storage and meridional energy transport, modulate the extent of these amplifications. This chapter underscores the significant influence of emission variability on regional hydrological projections and calls for more consistent modeling approaches in future multimodel projection efforts.

The second chapter further explores aerosol variability, specifically how interannual fluctuations in biomass burning emissions reduce the time-averaged magnitude of aerosol forcing. This work presents a mechanism that explains the intensification of the hydrologic cycle under increased aerosol variability described in the first chapter. It highlights that many emissions inventories overlook this variability, leading to possible overestimation of the cooling effect of aerosols and misrepresent the associated hydrological changes. The findings emphasize the need for improved representation of aerosol variability in climate models to better capture the spatial adjustments of the water cycle.

The third chapter introduces a new framework for understanding regional precipitation changes. This framework identifies three dominant contributors to regional precipitation shifts: global changes in evaporation, adjustments to the moisture cycling rate, and changes in atmospheric circulation. A key conclusion is that the global water cycling rate plays a critical role in explaining the spatial patterns of zonal-mean precipitation changes under warming. This framework provides a mechanistic understanding of regional precipitation shifts and enhances our ability to predict these changes under various warming scenarios.