[1] An extensive literature documents relations between reservoir storage capacity and water supply yield and the properties of instream flow needed to support downstream aquatic ecosystems. However, the literature that evaluates the impact of reservoir operating rules on instream flow properties is limited to a few site-specific studies, and as a result, few general conclusions can be drawn to date. This study adapts the existing generalized water evaluation and planning model (WEAP) to enable general explorations of relations between reservoir storage, instream flow, and water supply yield for a wide class of reservoirs and operating rules. Generalized relationships among these variables document the types of instream flow policies that when combined with drought management strategies, are likely to provide compromise solutions to the ecological and human negotiations for water for different sized reservoir systems. The concept of a seasonal ecodeficit/ecosurplus is introduced for evaluating the impact of reservoir regulation on ecological flow regimes.

Balancing human and environmental water resource needs is critical to environmental sustainability. In this paper two concepts are advanced. First, a methodology is introduced to evaluate water management policies and their impacts on the characteristics of both instream flow and water supply reliability. The concept of an "ecodeficit" is introduced to quantify the impact of changes to the natural flow regime resulting from human withdrawals. This metric provides a numerical and graphical representation of the tradeoff between human and ecological needs for available water. Second, we evaluate an approach that involves both simulation and optimization of alternative reservoir release policies. We demonstrate that by refining the quantity and timing of reservoir releases the reliability of a water supply yield can be substantially maintained while improving the satisfaction of ecological flows requirements. These two concepts are early applications of a more comprehensive ecological water supply management approach currently under development.

The sustainable development goals (SDGs) challenge markets, regulators and practitioners to achieve multiple objectives on water, food and energy. This calls for responses that are coordinated and scaled appropriately. Learning from waterenergy-food nexus could support much-needed building of links between the separate SDGs. The concept has highlighted how risks manifest when blinkered development and management of water, food and energy reduce resource security across sectors and far-reaching scales. However, three under-studied dimensions of these risks must be better considered in order to identify leverage points for sustainable development: first, externalities and shared risks across multiple scales; second, innovative government mechanisms for shared risks; and third, negotiating the balance between silos, politics and power in addressing shared risks.

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