UC Merced

Decisions on water allocation to humans and the environment depend on physical engineering structures, various operations and allocation policies, supplies, and demands of numerous end-users. Different assumptions of current and future scenarios can anticipate decisions that best meet human and environmental objectives, under different stressors (e.g., climate change, increased demands). Environmental water allocation especially presents intricate challenges, given the interplay of various regulations and the complexities of managing water resources across different regions. Therefore, the goal of this collection of studies is to provide new insights on reservoir operations, hydropower generation and water management in the Central Sierra Nevada, California, aiming to balance human demands, while achieving greater environmental benefits. This work involves the use of a novel method for water-power modeling with a specific application to the Central Sierra Nevada, California introduced in Chapter 1, and used in Chapters 2 and 4. The modeling framework includes more detailed and facility-specific information to provide a more comprehensive and finer temporal resolution (daily time-step) of water allocation decisions than those found in most modeling efforts. This is a potentially crucial method for modeling water management, due to the reconciliation of water and power systems through the integration of hydroeconomic needs (e.g., hydropower operations) and rule-based simulation (e.g., instream flow requirements), which is one of the biggest challenges in modeling water systems. Better representation of real-world systems is essential to address the difficulties in water management and to analyze solutions. These models are made available for use in a broad range of scenario analyses, including different hydrological inputs (historical and future climates), electricity prices, and a variety of management objectives. Chapter 2 delves into the nuanced landscape of environmental flow (e-flows) requirements, primarily anchored on water year types (WYTs), to understand the efficacy and adaptability of current strategies. Through an extensive examination of pertinent hydropower licensing documents, the research identifies a lack of standardized adoption of WYTs in many river reaches, manifesting as minimal variation across different year types and limited seasonal fluctuations. Incorporating climate change projections from multiple Global Circulations Models, the study reveals significant variability in WYT distributions under existing management strategies. This variability has led to inconsistencies in e-flow management, exacerbating potential conflicts among stakeholders. To address these challenges, an adaptive strategy is proposed, employing a method to recalibrate WYT thresholds, aiming to bolster the reliability and resilience of e-flows. As a result, Chapter 3 critically analyzes the systemic barriers hindering the effective implementation of e-flows. A comprehensive systematic review and bibliometric analysis were conducted, yielding insights into the major impediments such as competing priorities of human water uses, data deficiencies, and resource and capacity limitations. To enhance the successful implementation of e-flows, the dissertation recommends a system analysis approach, utilizing modeling tools to navigate competing demands and foster holistic flow allocations based on hydroecological principles. In turn, Chapter 4 evaluates the resilience of water systems and hydropower against climate whiplash. Through 200 synthetic hydrologic sequences of different lengths of dry-wet-dry combinations, the research underscores the vulnerability of water storage and the implications for water resource management, offering policy suggestions to enhance system flexibility and resilience against climatic shocks. Finally, Chapter 5 concludes by providing policy insights and recommendations based on these studies to help inform stakeholders and decision-makers in the search for sustainable solutions to water management problems.