Doctoral Dissertations

Date of Award

12-2025

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Civil Engineering

Major Professor

Joshua S. Fu

Committee Members

Forrest M. Hoffman, Jia Xing, Russell L. Zaretzki

Abstract

Extreme climate variability and limited air quality monitoring coverage continue to challenge environmental planning and public health protection. This dissertation investigates two major aspects of environmental risk in the contiguous United States: the evolution of drought under future climate conditions and the improvement of ground level PM2.5 estimation using an integrated modeling framework. The first part evaluates drought projections under the SSP5-8.5 scenario using a six member CMIP6 ensemble dynamically downscaled with a Regional Climate Model version 4 (RegCM4). Three drought indices, the Self Calibrating Palmer Drought Severity Index (ScPDSI), the 12 month Standardized Precipitation Index (SPI-12), and the 12 month Standardized Precipitation Evapotranspiration Index (SPEI-12), are applied to assess projected drought patterns across the contiguous United States for the near future and mid century periods. Results show that mild droughts become more frequent, while severe and extreme droughts generally decline. Persistent drying is projected in the western and southwestern regions due to long term soil moisture deficits. Although total drought exposure decreases after 2040, urban populations remain more affected than rural populations, indicating unequal vulnerability across regions. The second part develops a CMAQ machine learning framework to improve satellite based PM2.5 estimation. The approach integrates outputs from a chemical transport model with aerosol optical depth retrievals and extended surface monitoring networks. Including spatial and temporal features improves accuracy in rural and downwind regions where monitoring coverage is limited. The final part links drought and PM2.5 exposure to health and economic outcomes. Health impact assessments show that respiratory and cardiovascular diseases dominate the total burden, with urban populations experiencing three to five times higher risks than rural areas. National drought related health costs exceed 40 billion USD in the early decades, while PM2.5 related impacts surpass 100 billion USD each year. These findings highlight that climate driven environmental stressors impose substantial and unequal burdens on human health and economic wellbeing across the United States.

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