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201660 https://hdl.handle.net/2286/R.2.N.201660 http://rightsstatements.org/vocab/InC/1.0/ All Rights Reserved 2025 275 pages Doctoral Dissertation Academic theses en Alonso Vicario, Sara Garcia, Margaret Hornberger, George M. Mazzolen, Maurizio Mascaro, Giuseppe Arizona State University Partial requirement for: Ph.D., Arizona State University, 2025 Field of study: Civil, Environmental and Sustainable Engineering Human activities are reshaping the hydrological cycle across various spatial scales, from groundwater systems to major river basins and regional climates. Water acts as the essential element that connects and sustains all ecological functions and human societies. It influences climate regulation and energy balances, supports energy and food systems, and ensures water availability for households and agriculture. However, growing anthropogenic pressures from overuse and pollution are disrupting these vital functions. In some regions, this has led to severe ecosystem degradation, including aquifer depletion, habitat loss, nutrient overloading, and the collapse of water-dependent ecosystems. The multiple ways in which humans alter the hydrological cycle are not yet fully understood, as they vary across space and time and differ in magnitude. These changes range from global warming to more localized actions such as land use change, water withdrawal, and dam construction. Moreover, isolating the effects of human actions is challenging, as they often interact with climate, vegetation, soil properties, and other landscape factors, leading to complex runoff responses. Enhancing our understanding of these interactions and isolating human impacts is essential for a better water resources management and preparation for future changes. This thesis contributes to that understanding by examining the effects of human activities on the hydrological cycle in the United States. It also evaluates water utilities' vulnerability to future changes and potential adaptation strategies as anthropogenic pressures continue to grow. The first study investigates how urbanization, agriculture, and regulation explain differences in long-term water balances across the contiguous United States. The second study evaluates how these same activities have influenced streamflow droughts over the past four decades and identifies regional differences related to specific human activities. Finally, the third study assesses a California water utility's vulnerability to worsening droughts and potential adaptation strategies. Hydrologic sciences Civil Engineering Water resources management Droughts Land use Streamflow urban droughts water balances water supply Human Influences on the Hydrological Cycle: From Flows to Management