Hydropeaking affects downstream ecosystems and water uses. We assessed the effect of small re-regulation reservoirs (RRR) located downstream of hydropower plants to mitigate the impact of ...hydropeaking operations, in terms of the tradeoffs between flashiness of flows and power system cost. The study is performed on a hypothetical power system composed by one reservoir hydropower plant, one coal-fired plant, one diesel-fired plant, and one wind power plant. Hourly operations within a weekly horizon by each plant are prescribed by a system-wide cost-minimization model. Operations are constrained by minimum flows (MIF) and maximum ramping rates (MRR). The model was run for selected weeks, representative of the four seasons and three water year types. Results show that MIF and MRR constraints can achieve improvements in the flashiness of flows, from Richard-Baker index above 0.8 down to less than 0.1. However, without a RRR, these constraints can cause a power system cost increase of up to 70% with respect to the unconstrained case. The strongest effect on power system costs is observed under the dry hydrologic scenario. The cost increase is also significant in the summer weeks of the two normal scenarios. A half-hour capacity RRR keeps the cost increase below 8% and further reduces the flashiness to values below 0.1, on average for the dry scenarios. RRR storage capacities of one and 2 h can further reduce the cost increase below 5%, with flashiness as low as 0.01. No significant improvement is observed beyond this RRR size. In synthesis, this study shows that small re-regulation reservoirs, with capacities up to 2-h detention time, are a promising alternative for hydropeaking control at low power system cost.
•Environmental constraints for hydropeaking control cause large power cost increase.•Environmental constraints are effective in reducing subdaily hydrologic alteration.•Small re-regulation reservoirs can alleviate hydropower-ecosystem tradeoffs.
What is the relationship between inventory and sales? Clearly, inventory could increase sales: expanding inventory creates more choice (options, colors, etc.) and might signal a popular/desirable ...product. Or, inventory might encourage a consumer to continue her search (e.g., on the theory that she can return if nothing better is found), thereby decreasing sales (a scarcity effect). We seek to identify these effects in U.S. automobile sales. Our primary research challenge is the endogenous relationship between inventory and sales—e.g., dealers influence their inventory in anticipation of demand. Hence, our estimation strategy relies on weather shocks at upstream production facilities to create exogenous variation in downstream dealership inventory. We find that the impact of adding a vehicle of a particular model to a dealer’s lot depends on which cars the dealer already has. If the added vehicle expands the available set of submodels (e.g., adding a four-door among a set that is exclusively two-door), then sales increase. But if the added vehicle is of the same submodel as an existing vehicle, then sales actually decrease. Hence, expanding variety across submodels should be the first priority when adding inventory—adding inventory within a submodel is actually detrimental. In fact, given how vehicles were allocated to dealerships in practice, we find that adding inventory actually lowered sales. However, our data indicate that there could be a substantial benefit from the implementation of a “maximize variety, minimize duplication” allocation strategy: sales increase by 4.4% without changing the total number of vehicles at each dealership.
This paper was accepted by Vishal Gaur, operations management.
•A novel modeling setup was developed to simulate the reverse flow phenomenon.•Lake’s tributaries and the Mekong River played virtually the same role.•Less negative impacts on the current flow regime ...change in Tonle Sap Lake were attributed to China.
The flow regime of the largest lake in Southeast Asia, Tonle Sap Lake, is driven by the reverse flow phenomenon caused by its link with the Mekong River. This reverse flow makes the lake one of the most productive aquatic ecosystems globally and thus provides important economic opportunities for local communities. The recent human activities in the upstream, as well as climate variations, have resulted in unforeseen alterations in the reverse flow. However, little is known about the explicit attribution of different parts of the upstream basin to these variations, which would be essential for transboundary water management. To unveil these attributions, we developed a novel modeling setup consisting of hydrodynamic, hydrological, and machine learning models. This modeling setup allowed us to separate the impacts of a) climate variation, b) human activities in the Chinese part of the basin, and b) the lower part of the basin (i.e., Laos, Thailand, and Vietnam). During the 2001–2009 baseline, when human modifications to the flow were still minimal, we found that Tonle Sap Lake received, on average, 42.4 km3/yr water from the Mekong, 48.2 % of the total inflow to the lake. During the period of increased human activities, 2010–2020, this decreased due to climate variation to 40.1 km3/yr (a 5.7 % drop), which was further exacerbated by the increased human activities in the upstream parts of the basin (China ∼ 7.3 %, Laos, Thailand, and Vietnam ∼ 9 %). Additionally, during the flow period when water flows from the lake towards the Mekong, on average, 31 % of the total inflow into the Mekong Delta originated from the lake during the baseline period. Climate variation decreased this by 4 percentage points (pp), i.e., to 27 %, while the human activities in China and lower parts of the basin decreased this by 1.6 pp (25.4 %) and 1.9 pp (25.1 %), respectively. Our findings unveiled the attributions of different drivers on Tonle Sap Lake’s hydrology and will facilitate transboundary water management in the basin. The impacts of future plans on different parts of the basin should be carefully evaluated together with existing anthropogenic impacts, as well as climate change, to minimize the further impacts on the lake.
The quarantine of identified close contacts has been vital to reducing transmission rates and averting secondary infection risk before symptom onset and by asymptomatic cases. The effectiveness of ...this contact tracing strategy to mitigate transmission is sensitive to the adherence to quarantines, which may be lower for longer quarantine periods or in vaccinated populations (where perceptions of risk are reduced). This study develops a simulation model to evaluate contact tracing strategies based on the sequential testing of identified contacts after exposure as an alternative to quarantines, in which contacts are isolated only after confirmation by a positive test. The analysis considers different number and types of tests (PCR and lateral flow antigen tests (LFA)) to identify the cost-effective testing policies that minimize the expected infecting days post-exposure considering different levels of testing capacity. This analysis suggests that even a limited number of tests can be effective at reducing secondary infection risk: two LFA tests (with optimal timing) avert infectiousness at a level that is comparable to 14-day quarantine with 80-90% adherence, or equivalently, 7-9 day quarantine with full adherence (depending on the sensitivity of the LFA test). Adding a third test (PCR or LFA) reaches the efficiency of a 14-day quarantine with 90-100% adherence. These results are robust to the exposure dates of the contact, test sensitivity of LFA and alternative models of viral load evolution, which suggests that simple testing rules can be effective for improving contact tracing in settings where strict quarantine adherence is difficult to implement.
Water management usually considers economic and ecological objectives, and involves tradeoffs, conflicts, compromise, and cooperation among objectives. Pareto optimality often is championed in water ...management, but its relationships with the mathematical representation of objectives, and implications of tradeoffs for Pareto optimal decisions, are rarely examined. We evaluate the mathematical properties of optimized tradeoffs to identify promising regions for compromise, suggest strategies for reducing conflicts, and better understand whether decision‐makers are more or less likely to cooperate on environmental water allocations. Cooperation and compromise among objectives can be easier when tradeoff curves are concave and more adversarial when tradeoff curves are convex. “Knees,” or areas with maximum curvature, bulges, or breakpoints in concave Pareto frontiers, suggest more promising areas for compromise. Evaluating the shape of Pareto curves based on each objective's performance function can screen for the existence of knees amenable to compromise. We explore water management and restorations actions that improve and shift the location and prominence of knees in concave Pareto frontiers. Connecting river habitats and other non‐flow management actions may add knees on locally concave regions of Pareto frontiers. Managing multiple streams regionally, rather than individually, can sometimes turn convex local tradeoffs into concave regional tradeoffs more amenable to compromise. Overall, this analysis provides a deep investigation of how the shape of tradeoffs influences the range and promise of decisions to improve performance, and illustrates that management actions may encourage cooperation and reduce conflict.
Plain Language Summary
Water management usually considers economic and ecological objectives, and involves tradeoffs, conflicts, compromise, and cooperation among objectives. We evaluate the mathematical properties of tradeoffs to identify promising regions for compromise, suggest strategies for reducing conflicts, and better understand whether decision‐makers are more or less likely to cooperate on environmental water allocations. Cooperation and compromise among objectives can be easier when tradeoff curves are concave and more adversarial when tradeoff curves are convex. "Knees", or areas with maximum curvature, bulges, or breakpoints in concave tradeoffs, suggest more promising areas for compromise. We explore water management and restorations actions that improve and shift the location and prominence of knees in concave tradeoff curves. Connecting river habitats and other non‐flow management actions may add knees on locally concave regions of tradeoffs curves. Managing multiple streams regionally, rather than individually, can sometimes turn convex local tradeoffs into concave regional tradeoffs more amenable to compromise. Overall, this analysis provides an investigation of how the shape of tradeoffs influences the range and promise of decisions to improve performance, and illustrates that management actions may encourage cooperation and reduce conflict.
Key Points
The shape of the Pareto frontier influences whether decision‐makers are more or less likely to cooperate over environmental water allocations
Compromise is more likely where knees, or areas of maximum curvature, occur in concave tradeoff frontiers
Management actions, like non‐flow improvements to objectives can expand the Pareto curve and improve optima for one or both objectives
In sequential competitions, the order in which teams take turns may have an impact on performance and the outcome. Previous studies with penalty shootouts have shown mixed evidence of a possible ...advantage for the first shooting team. This has led to some debate on whether a change in the rules of the game is needed. This work contributes to the debate by collecting an extensive dataset of shootouts which corroborates an advantage for the first shooter, albeit with a smaller effect than what has been documented in previous research. To evaluate the impact of alternative ordering of shots, we model shootouts as a probability network, calibrate it using the data from the traditional ordering, and use the model to conduct counterfactual analysis. Our results show that alternating the team that shoots first in each round would reduce the impact of ordering. These results were in part developed as supplement to field studies to support the International Football Association Board's (IFAB) consideration of changing the shooting order.
The newsvendor model captures the trade-off faced by a decision maker that needs to place a firm bet prior to the occurrence of a random event. Previous research in operations management has mostly ...focused on deriving the decision that minimizes the expected mismatch costs. In contrast, we present two methods that estimate the unobservable cost parameters characterizing the mismatch cost function. We present a structural estimation framework that accounts for heterogeneity in the uncertainty faced by the newsvendor as well as in the cost parameters. We develop statistical methods that give consistent estimates of the model primitives, and derive their asymptotic distribution, which is useful to do hypothesis testing. We apply our econometric model to a hospital that balances the costs of reserving too much versus too little operating room capacity to cardiac surgery cases. Our results reveal that the hospital places more emphasis on the tangible costs of having idle capacity than on the costs of schedule overrun and long working hours for the staff. We also extend our structural models to incorporate external information on forecasting biases and mismatch costs reported by the medical literature. Our analysis suggests that overconfidence and incentive conflicts are important drivers of the frequency of schedule overruns observed in our sample.
Irrigated agriculture is indispensable to the Lower Mekong River Basin (LMB), which ensures food security and provides livelihoods for tens of millions of people. Irrigation, agricultural production, ...hydropower and aquatic ecosystem health are intertwined in LMB, so it is necessary to adopt a holistic approach to analyze irrigation problems. Here, we discuss the challenges and opportunities of LMB irrigation. Bibliometric analysis is carried out to determine the characteristics and patterns of watershed irrigation literature, such as the importance of authors, affiliated institutions, and their distribution in China. Based on bibliometric analysis, research topics are determined for thematic review. Firstly, we investigated the factors that directly affect the demand and supply of irrigation water and associated crop yield impacts. Secondly, we analyzed the influence of water availability, land use and climate change on agricultural irrigation. Thirdly, we analyzed the adverse effects of improper irrigation management on the environment, such as flow pattern change, ecosystem deterioration and land subsidence caused by groundwater overexploitation. Fourthly, the time–space mismatch between water supply and demand has brought serious challenges to the comprehensive water resources management in cross-border river basins. In each specific application area, we sorted out the technologies in which remote sensing technology is used. We hope that this review will contribute to in-depth research and decision analysis of remote sensing technology in agricultural irrigation.
Understanding the development of water environmental regulations over time and its response to external stress is crucial to enhance its performance, but there are few studies on it. This study aims ...to unfold the evolution of water environmental regulations in Chile and its response to changing water resources management, socio-economic, climate, and environmental conditions from 1900 to 2019. Content analysis was used to code the water environmental regulations, whereas trend analysis was carried out to identify the development stages, and both qualitative and quantitative co-evolutionary approaches were used to analyze the response of water environmental regulations to external changes. Results show that the development of water environmental regulations experienced the following four stages: the pre-development (1900–1980), slow development (1981–1993), development (1994–2009), and fast development (2010–2019). The development of water environmental regulations seriously lagged from water resources management and linearly responded to economic development and population growth. However, it presented a weak response to climate change and had a limited impact on environmental degradation. Development of water environment regulations should be integrated and synchronized with water resources management in future.
Hydrologic alteration due to hydropeaking reservoir operations is a main concern worldwide. Subdaily environmental flow constraints (ECs) on operations can be promising alternatives for mitigating ...negative impacts. However, those constraints reduce the flexibility of hydropower plants, potentially with higher costs for the power system. To study the economic and environmental efficiency of ECs, this work proposes a novel framework comprising four steps: (i) assessment of the current subdaily hydrologic alteration; (ii) formulation and implementation of a short‐term, grid‐wide hydrothermal coordination model; (iii) design of ECs in the form of maximum ramping rates (MRRs) and minimum flows (MIFs) for selected hydropower reservoirs; and (iv) identification of Pareto‐efficient solutions in terms of grid‐wide costs and the Richard‐Baker flashiness index for subdaily hydrologic alteration (SDHA). The framework was applied to Chile's main power grid, assessing 25 EC cases, involving five MIFs and five MRRs. Each case was run for a dry, normal, and wet water year type. Three Pareto‐efficient ECs are found, with remarkably small cost increase below 2% and a SDHA improvement between 28% and 90%. While the case involving the highest MIF worsens the flashiness of another basin, the other two have no negative effect on other basins and can be recommended for implementation.
Key Points:
Framework for Pareto‐efficient environmental flow constraints on hydropeaking
Compromise between grid‐wide cost and subdaily hydrologic alteration
Pareto‐efficient constraints are found with cost increase below 2%
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