Marcelo A. Olivares

Economic consequences of optimized water management for a prolonged, severe drought in California

If abrupt climate change has occurred in the past and may be more likely under human forcing, it is relevant to look at the adaptability of current infrastructure systems to severe conditions of the recent past. Geologic evidence suggests two extreme droughts in California during the last few thousand years, each 120-200 years long, with mean annual streamflows 40%-60% of the historical mean. This study synthesized a 72 year drought with half of mean historical inflows using random sampling of historical dry years. One synthetic hydrological record is used, and sensitivity to different interpretations of the paleorecord is not evaluated. Economic effects and potential adaptation of Californias water supply system in 2020 to this drought is explored using a hydroeconomic optimization model. The model considers how California could respond to such an extreme drought using water trading and provides best-case estimates of economic costs and effects on water operations and demands. Results illustrate the ability of extensive, intertied, and flexible water systems with heterogeneous water demands to respond to severe stress. The study follows a different approach to climate change impact studies, focusing on past climate changes from the paleorecord rather than downscaled general circulation model results to provide plausible hydrologic scenarios. Adaptations suggested for the sustained drought are similar for dry forms of climate warming in California and are expensive but not catastrophic for the overall economy but would impose severe burdens on the agricultural sector and environmental water uses.

ICU Admission Control: An Empirical Study of Capacity Allocation and Its Implication for Patient Outcomes

This work examines the process of admission to a hospitals intensive care unit ICU. ICUs currently lack systematic admission criteria, largely because the impact of ICU admission on patient outcomes has not been well quantified. This makes evaluating the performance of candidate admission strategies difficult. Using a large patient-level data set of more than 190,000 hospitalizations across 15 hospitals, we first quantify the cost of denied ICU admission for a number of patient outcomes. We use hospital operational factors as instrumental variables to handle the endogeneity of the admission decisions and identify important specification issues that are required for this approach to be valid. Using the quantified cost estimates, we then provide a simulation framework for evaluating various admission strategies performance. By simulating a hospital with 21 ICU beds, we find that we could save about

Grid-wide subdaily hydrologic alteration under massive wind power penetration in Chile

1.9 million per year by using an optimal policy based on observables designed to reduce readmissions and hospital length of stay. We also discuss the role of unobserved patient factors, which physicians may discretionarily account for when making admission decisions, and show that including these unobservables could result in a more than threefold increase in benefits compared to just optimizing the policy over the observable patient factors. n nThis paper was accepted by Serguei Netessine, operations management.

Representing Energy Price Variability in Long- and Medium- term Hydropower Optimization

Hydropeaking operations can severely degrade ecosystems. As variable renewable sources (e.g. wind power) are integrated into a power grid, fluctuations in the generation-demand balance are expected to increase. In this context, compensating technologies, notably hydropower reservoir plants, could operate in a stronger peaking scheme. This issue calls for an integrated modeling of the entire power system, including not only hydropower reservoirs, but also all other plants. A novel methodology to study the link between the short-term variability of renewable energies and the subdaily hydrologic alteration, due to hydropower reservoir operations is presented. Grid operations under selected wind power portfolios are simulated using a short-term hydro-thermal coordination tool. The resulting turbined flows by relevant reservoir plants are then compared in terms of the Richard-Baker flashiness index to both the baseline and the natural flow regime. Those are then analyzed in order to: i) detect if there is a significant change in the degree of subdaily hydrologic alteration (SDHA) due to a larger wind penetration, and ii) identify which rivers are most affected. The proposed scheme is applied to Chiles Central Interconnect System (SIC) for scenarios up to 15% of wind energy penetration. Results show a major degree of SDHA under the baseline as compared to the natural regime. As wind power increases, so does the SDHA in two important rivers. This suggests a need for further ecological studies in those rivers, along with an analysis of operational constraints to limit the SDHA.

A framework to identify Pareto‐efficient subdaily environmental flow constraints on hydropower reservoirs using a grid‐wide power dispatch model

Representing peak and off-peak energy prices is often difficult in hydropower modeling because the time scale of price variability (hours or less) is much shorter than that needed for many operations planning models (days to months). This work extends and examines the reliability of an existing approximate method to incorporate hourly energy price information into revenue functions used in hydropower reservoir optimization models with larger time steps (weekly or monthly). The method assumes constant head, an exogenously known frequency distribution for hourly prices during each modeled time period (day, week, or month), and a revenue-maximizing operational strategy that allocates hydropower releases in order of decreasing hourly price. The method is extended to the case with minimum instream flow requirements. The reliability of the method was tested for the cases with and without minimum instream flow requirements. Revenue estimates for a hypothetical hydropower site were compared with the exact optimal revenue from solving the hourly optimization problem within one week, and showed less than 1% error by using a finely discretized price-frequency curve.

Association Among Icu Congestion, Icu Admission Decision, and Patient Outcomes.

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 Chiles 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.

Extreme Drought and Water Supply Management in California

Objectives:To employ automated bed data to examine whether ICU occupancy influences ICU admission decisions and patient outcomes. Design:Retrospective study using an instrumental variable to remove biases from unobserved differences in illness severity for patients admitted to ICU. Setting:Fifteen hospitals in an integrated healthcare delivery system in California. Patients:Seventy thousand one hundred thirty-three episodes involving patients admitted via emergency departments to a medical service over a 1-year period between 2008 and 2009. Interventions:None. Measurements and Main Results:A third of patients admitted via emergency department to a medical service were admitted under high ICU congestion (more than 90% of beds occupied). High ICU congestion was associated with a 9% lower likelihood of ICU admission for patients defined as eligible for ICU admission. We further found strong associations between ICU admission and patient outcomes, with a 32% lower likelihood of hospital readmission if the first inpatient unit was an ICU. Similarly, hospital length of stay decreased by 33% and likelihood of transfer to ICU from other units—including ICU readmission if the first unit was an ICU—decreased by 73%. Conclusions:High ICU congestion is associated with a lower likelihood of ICU admission, which has important operational implications and can affect patient outcomes. By taking advantage of our ability to identify a subset of patients whose ICU admission decisions are affected by congestion, we found that, if congestion were not a barrier and more eligible patients were admitted to ICU, this hospital system could save approximately 7.5 hospital readmissions and 253.8 hospital days per year. These findings could help inform future capacity planning and staffing decisions.

Assessing the effect of fish size on species distribution model performance in southern Chilean rivers

The geological record contains extreme droughts beyond those seen in historical hydrologic records. For California, the geological record contains several extreme droughts the last few thousand years. Two of these droughts are 120-200 years long, with mean annual streamflows between 40% and 60% of the historical mean. This study synthesized a 72-year historical record for a drought of this character, having a mean flow of 40% of the historical record. This hydrologic time series was used as input to an economic-engineering optimization model of California’s water supply system (CALVIN). The model allows exploration of how California’s water management system might respond to such an extreme drought and provides preliminary estimates of economic costs and effects of such a drought on water operations and demands. The overall results show the importance of management flexibility and adaptation in response to extreme stresses on water systems. Results also illustrate the physical ability of extensive, diversified, and highly intertied water systems with heterogeneous water demands to economically respond to such extreme stresses. The study provides a different approach to climate change studies, focusing on observed past changes in climate from the geologic record rather than downscaled general circulation model results to provide hydrologic scenarios.

Adaptability and adaptations of California’s water supply system to dry climate warming

Despite its theoretical relationship, the effect of body size on the performance of species distribution models (SDM) has only been assessed in a few studies of terrestrial taxa. We aim to assess the effect of body size on the performance of SDM in river fish. We study seven Chilean freshwater fish, using models trained with three different sets of predictor variables: ecological (Eco), anthropogenic (Antr) and both (Eco+Antr). Our results indicate that the performance of the Eco+Antr models improves with fish size. These results highlight the importance of two novel predictive layers: the source of river flow and the overproduction of biotopes by anthropogenic activities. We compare our work with previous studies that modeled river fish, and observe a similar relationship in most cases. We discuss the current challenges of the modeling of riverine species, and how our work helps suggest possible solutions.