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Recent studies have demonstrated some advantages of using advanced heuristic algorithms to identify near-Pareto-optimal future locations, types, and sizes for stormwater low-impact development and green infrastructure (LID/GI) across a given urban landscape. However, previous optimization studies did not consider social equity as an objective, which poses problems because urban green infrastructure often is distributed inequitably. Increasing access to LID/GI in historically marginalized areas is a prominent environmental justice issue, and increasingly is becoming a primary consideration when prioritizing future locations, types, and sizes of urban LID/GI. This study integrated a novel spatial social equity objective [LID/GI–Social Vulnerability Index (SVI) correlation objective, ρ ] into a multiobjective LID/GI optimization model. The LID/GI-SVI correlation is an objective that directs the optimization algorithm to search for LID/GI distributions that maximize the linear correlation between LID/GI implementation and subbasins with higher estimated percentages of historically marginalized people. Our analysis focused on understanding the impacts of the LID/GI-SVI correlation objective on a LID/GI optimization model. This modeling study demonstrates that (1) the LID/GI-SVI correlation objective can be used to direct optimization algorithms to search for LID/GI distributions that can achieve runoff management objectives, increase green LID/GI implementation in more marginalized areas, and explore the potential trade-offs or synergies between hydrologic and equity goals; (2) LID/GI optimization formulations that consider only hydrologic objectives likely will not result in equitable LID/GI distributions; (3) LID/GI distributions that perform well on the LID/GI-SVI correlation may be composed of different types of LID/GI than less-equitable but more hydrologically favorable LID/GI distributions; and (4) for our study area, including spatial equity as an objective resulted in modest reductions in the hydrologic performance of near-Pareto-optimal LID/GI distributions. Low-impact development or stormwater green infrastructure (LID/GI) has been implemented across the globe to address the environmental issues of increased impervious surfaces, aging infrastructure, elevated stormwater runoff due to climate change, and to meet non-point-source discharge permit requirements. Recent research has demonstrated the use of advanced algorithms to help identify optimal locations, sizes, and types of LID/GI that will maximize local runoff reduction benefits. Although runoff control is a primary objective of LID/GI, many cities in the US have been striving to prioritize local areas with high proportions of historically underserved or vulnerable populations for implementation. In tune with this trend, we developed a novel equity objective function that forces a proportional relationship between LID/GI implementation and indicators of social vulnerability. We tested the impact of this new objective within a multiobjective LID/GI optimization algorithm and found minimal trade-offs between runoff and equity objectives in our study area. [ABSTRACT FROM AUTHOR]

Spatially distributed hydrologic models are commonly employed to optimize the locations of engineering control measures across a watershed. Yet, parameter screening exercises that aim to reduce the dimensionality of the calibration search space are typically completed only for gauged locations, like the watershed outlet, and use screening metrics that are relevant to calibration instead of explicitly describing decision objectives. Identifying parameters that control physical processes in ungauged locations that affect decision objectives should lead to a better understanding of control measure effectiveness. This paper provides guidance on evaluating model parameter uncertainty at the spatial scales and flow magnitudes of interest for such decision-making problems. We use global sensitivity analysis to screen parameters for model calibration, and to subsequently evaluate the appropriateness of using parameter multipliers to further reduce dimensionality. We evaluate six sensitivity metrics that align with four decision objectives; two metrics consider model residual error that would be considered in spatial optimizations of engineering designs. We compare the resulting parameter selection for the basin outlet and each hillslope. We also compare basin outlet results to those obtained by four calibration-relevant metrics. These methods were applied to a RHESSys ecohydrological model of an exurban forested watershed near Baltimore, MD, USA. Results show that 1) the set of parameters selected by calibration-relevant metrics does not include parameters that control decision-relevant high and low streamflows, 2) evaluating sensitivity metrics at only the basin outlet does not capture many parameters that control streamflows in hillslopes, and 3) for some parameter multipliers, calibration of just one of the parameters being adjusted may be the preferred approach for reducing dimensionality. Thus, we recommend that parameter screening exercises use decision-relevant metrics that are evaluated at the spatial scales appropriate to decision making. While including more parameters in calibration will exacerbate equifinality, the resulting parametric uncertainty should be important to consider in discovering control measures that are robust to it. [ABSTRACT FROM AUTHOR]

Engineering systems are designed to be robust to low-probability, high-consequence hazards. The concept of robustness has been crucial to the safety of our built environment. However, increasing robustness to one hazard must come at the expense of performance on other objectives. An interesting question is: Can we avert these opportunity costs by better conditioning water management decisions on forecasts? This study explores this question in the Red River Basin of Vietnam, where a system of reservoirs must simultaneously produce hydroelectric power, provide water to meet agricultural, municipal and environmental demands and, most importantly, prevent loss of life by protecting the capital city of Hanoi from devastating floods. The Vietnamese government seeks to use these reservoirs to provide protection to the 500-yr flood and has independently designed their own operating guidelines with this goal. However, optimizing operating policies to meet the multiple sectoral demands while providing protection to the 500-yr flood reveals that meeting this requirement with existing infrastructure is non-trivial. Policies exist that meet this goal under stationary hydrologic conditions, but doing so requires major sacrifices in performance on hydropower and water supply objectives. These tradeoffs are exacerbated if stakeholders also desire robust performance across potential hydrologic and socioeconomic futures; compared to optimizing to the 100-yr flood, it is far more difficult to find policies that also meet minimum performance requirements on hydropower and deficit objectives across a broad range of futures. Conditioning operations on a naïve forecast is partly able to close the gap, though, suggesting more sophisticated forecast products may hold promise in reducing the multi-sectoral consequences of robustness to severe flood events. Future work will explore the potential for seasonal climate forecasts to close the remaining gap and allow for robust flood protection at no cost. [ABSTRACT FROM AUTHOR]