Globally, urban water managers are increasingly challenged by growing water demands and a changing climate (AghaKouchak et al., 2021;Wasley et al., 2020). In the United States (US), drinking water systems require over $400 billion of capital investment by 2029 to maintain aging infrastructure and manage growing demands (ASCE, 2021

Urban water utilities, facing rising demands and limited supply expansion options, increasingly partner with neighboring utilities to develop and operate shared infrastructure. Inter‐utility agreements can reduce costs via economies of scale and help limit environmental impacts, as substitutes for independent investments in large capital projects. However, unexpected shifts in demand growth or water availability, deviating from projections underpinning cooperative agreements, can introduce both supply and financial risk to utility partners. Risks may also be compounded by asymmetric growth in demand across partners or inflexibility of the agreement structure itself to adapt to changing conditions of supply and demand. This work explores the viability of both fixed and adjustable capacity inter‐utility cooperative agreements to mitigate regional water supply and financial risk for utilities that vary in size, growth expectations, and independent infrastructure expansion options. Agreements formalized for a shared regional water treatment plant are found to significantly improve regional supply reliability and financial outcomes, despite highly correlated weather and climate across neighboring supply systems (e.g., concurrent drought events). Regional improvements in performance, however, mask tradeoffs among individual agreement partners. Adjustable treatment capacity allocations add flexibility to inter‐utility agreements but can compound financial risk to each utility as a function of the decision‐making of the other partners. Often the sensitivity to partners' decision‐making under an adjustable agreement degrades financial performance, relative to agreements with fixed capacities allocated to each partner. Our results demonstrate the significant benefits cooperative agreements offer, providing a template to aid decision‐makers in the development of water supply partnerships.

Key Takeaways Capacity‐sharing agreements can help water utilities make use of spare capacity while long‐run demands catch up with projections by allocating project capacity and splitting infrastructure costs between multiple utilities. Utility size, projected growth, and regional context all can influence the most effective choice of capacity‐sharing agreement. Analysis of cooperative agreements can inform utility managers on how to effectively design and implement agreements of their own.

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Climate and land cover change strongly shape water resources management, but understanding their joint impacts is extremely challenging. Consequently, there is limited research of their integrated effects on water supply systems, and even fewer studies that rigorously account for infrastructure investment and management interventions. We utilize ecohydrologic modeling to generate watershed outflows under scenarios of climate and land cover change, which in turn drive modeled water utility-level decision making for the Research Triangle region of North Carolina. In the Triangle region, land cover and climate change are both likely to increase water supply availability (reservoir inflows) individually and in tandem. However, improvements from water supply increases are not uniform across management system performance indicators of reliability, conservation implementation frequency (i.e., water use restrictions), and infrastructure investment. Utility decisions influence the impact of hydrologic change through both short-term (e.g., use restrictions and water transfers) and longer-term infrastructure investment actions, in some cases offsetting the beneficial effects of additional water supply. Timing and sequencing of infrastructure development are strongly sensitive to climate and land use change as captured by their impacts on utility performance outcomes. This work underscores the need to consider adaptive management system responses and decision-relevant performance measures when determining the impacts of hydrologic change on water availability. Key Points: • Utility-scale decision making influences the impact of climate and land use change on both short-and long-term outcomes • Timing and sequencing of infrastructure development is highly sensitive to hydrologic change as captured by utility performance indicators • Impacts of hydrologic change are not uniform across performance indicators, utilities, or time, owing to management actions Supporting Information: • Supporting Information S1 Vose, J. M., Coulston, J. W., et al. (2020). Accounting for adaptive water supply management when quantifying climate and land cover change vulnerability. Water Resources Research, 56, e2019WR025614. https://

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Regionalization approaches wherein utilities in close geographic proximity cooperate to manage drought risks and co-invest in new infrastructure are increasingly necessary strategies for leveraging economies of scale to meet growing demands and navigate deeply uncertain risks. Successful regional cooperative investment and management pathways, however, must equitably balance the interests of multiple partners while navigating power relationships between regional actors. In long-term infrastructure planning contexts, this challenge is heightened by the evolving system-state dynamics, which may be fundamentally reshaped by infrastructure investment. This work introduces Equitable, Robust, Adaptive, and Stable Deeply Uncertain Pathways (DU PathwaysERAS), an exploratory modeling framework for developing regional water supply management and infrastructure investment pathways. Our framework explores equity and power relationships within cooperative pathways using multiple rival framings of robustness, each representing a competing hypothesis about how performance objectives should be prioritized. To capture the time-evolving dynamics of infrastructure pathways, DU PathwaysERAS features new tools to measure the adaptive capacity of pathway policies and evaluate time-evolving vulnerability. We demonstrate our framework on a six-utility water supply partnership seeking to develop cooperative infrastructure investment pathways in the Research Triangle, North Carolina. Our results indicate that commonly employed framings of robustness can have large and unintended adverse consequences for regional equity. Results further illustrate that regional and individual vulnerabilities are highly interdependent, emphasizing the need to craft agreements that limit counterparty risks from the actions of cooperating partners. Beyond the Research Triangle, these results are broadly applicable to cooperative water supply infrastructure investment and management globally.

Using municipal wastewater effluent as a feedstock in algae cultivation is a promising approach for increasing the commercial viability of algal biofuel production. However, differences in site-specific characteristics at municipal wastewater treatment plants (WWTPs) could drive tradeoffs between maximizing the profitability of algae production and minimizing the cost of meeting water quality standards. A complicating factor is how water quality regulations are enforced, namely the potential presence of nutrient trading markets that would monetize removal of nutrients from wastewater effluent. This study develops an analytical framework for optimizing the siting of an algal biofuel production facility within a network of WWTPs. A combined life cycle assessment (LCA) and techno-economic analysis (TEA) model of an algal biofuel production facility is integrated with a simplified watershed model. An evolutionary algorithm is used to identify optimal sites for algal biofuel production and explore financial tradeoffs for algae biofuel producers and wastewater treatment plants. This analytical framework is then applied to a high-priority, impaired watershed in North Carolina, the Neuse River Basin.