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•Arguments for the importance of diversity within scenario sets are developed.•The diversity of six global scenario sets is assessed.•Results show relatively good performance with ...regards to scenario set diversity.•There is a trade-off between covering the scenario space and redundancy.
Scenario development and analysis is an important methodological approach in the assessment of global environmental change. Scenarios are used to assess climate change and its impacts on societies, economies, and ecosystems, and identify, test, and improve policy responses to manage the negative consequences of a changing environment. Evaluation of scenarios, especially global scenarios widely used in the climate research and policy community, is therefore urgently needed. While the quality and usefulness of individual scenarios have been extensively examined through a wide array of criteria, standards for systematic evaluation of scenario sets are only emerging. Scenario diversity (i.e., diversity between individual scenarios in a set) has been advanced as a measure to assess the quality of global scenario sets. In this paper, we use scenario diversity analysis, a systematic and transparent quantitative method, to examine six major global scenario sets with regards to scenario set diversity. Results show that the assessed scenario sets show relatively good performance with regards to scenario set diversity. However, the use of classic methods for building scenario architectures and the number of scenarios included in a set raise important questions about the potential trade-offs between covering a bigger space of futures possibilities and adding redundancy to the scenario set.
Scenario planning is a popular approach for addressing uncertainty in strategic decision making. An open and adaptable approach from its inception, scenario planning has developed into separate ...schools and is now used across a wide range of research fields and practical settings. Reviews point to three challenges that limit the spread and the usefulness of scenario planning: conceptual confusion, methodological chaos, and scarcity of evidence on its effectiveness. This review of reviews brings together recent insights offered by the literature that suggest that these challenges have been partly met. A recent proposal for a synthesized definition of what a scenario is turns out to capture novel definitions quite well. The overarching term scenario planning covers a confusing diversity of methods and techniques. Nevertheless, within each of the separate schools the range of methodological choices is more restricted and arguments for choosing between options are clearer. Finally, while there is indeed a scarcity of research into effectiveness of scenario planning, on the level of specific techniques there is evidence of impact. This paper contributes to the literature on scenario analysis. For practitioners this paper provides more clarity on how to implement scenario planning, in terms of available process designs, how to choose between them and which techniques can help in implementation and how to measure effectiveness.
•Scenarios are plausible sets of narrated alternatives.•Its construction may include participation, time, goal, and validation.•Different schools highlight the external factors, coherent narrative, differentiated sets, uncertainty and knowledge.•Most used techniques are dynamic scenarios and cognitive fuzzy maps.•A detailed adherance to the technical process can improve scenario practice and reporting for effectiveness.
To address the unprecedented increase in China's CO
emissions over the past decades, the Chinese government has implemented many policies that are aimed at reducing carbon intensity. Applying the ...LMDI method, this study conducts a decomposition analysis of the drivers influencing China's CO
emissions by examining the details of 41 industry sub-sectors during 2000-2016; further, it predicts the carbon intensity reduction potential in 2020 and 2030 based on various official policies and documents. We conclude that energy intensity was the primary indicator that reduced CO
emissions, whereas the effects of carbon intensity, energy mix, and industrial structure were relatively minor. During the study period, the effect of industrial structure optimization on the change in CO
emissions shifted from the promotion of emissions to their suppression, with the inhibiting influence becoming greater over time. Finally, scenario analysis indicated that CO
intensity would decrease 21.5% by 2020 compared to the 2015 level, and the reduction target of 65% would be achieved fully in 2030 in the outlook scenario. Energy intensity is the largest contributor to the decrease in CO
emissions during 2016-2020, whereas industrial structure optimization shows the greatest potential for environmental improvement during 2020-2030. This paper concludes that more stringent policies are essential to reducing CO
emissions in the near future.
Many practical applications in control require that constraints on the inputs and states of the system are respected, while some performance criterion is optimized. In the presence of model ...uncertainties or disturbances, it is often sufficient to satisfy the state constraints for at least a prescribed share of the time, such as in building climate control or load mitigation for wind turbines. For such systems, this paper presents a new method of Scenario-Based Model Predictive Control (SCMPC). The basic idea is to optimize the control inputs over a finite horizon, subject to robust constraint satisfaction under a finite number of random scenarios of the uncertainty and/or disturbances. Previous SCMPC approaches have suffered from a substantial gap between the rate of constraint violations specified in the optimal control problem and that actually observed in closed-loop operation of the controlled system. This paper identifies the two theoretical explanations for this gap. First, accounting for the special structure of the optimal control problem leads to a substantial reduction of the problem dimension. Second, the probabilistic constraints have to be interpreted as average-in-time, rather than pointwise-in-time. Based on these insights, a novel SCMPC method can be devised for general linear systems with additive and multiplicative disturbances, for which the number of scenarios is significantly reduced. The presented method retains the essential advantages of the general SCMPC approach, namely a low computational complexity and the ability to handle arbitrary probability distributions. Moreover, the computational complexity can be adjusted by a sample-and-remove strategy.
Policy, technology, and economic uncertainties affect the net benefits of grid reinforcements, and should be considered in planning. Stochastic optimisation can improve the robustness and expected ...performance of transmission plans, but is computationally intensive because model size grows as more scenarios are considered. Therefore, the ability to find a small number of scenarios while still capturing the benefits of stochastic programming is crucial. In this study, the authors evaluate the performance of several promising scenario sampling methods. Criteria for comparison include an index of the economic consequences of simplifying scenarios (the expected cost of naïve solution), changes in first-stage investment decisions, and maximum regret. The results of an application to multidecadal planning of the Western Electricity Coordinating Council system show that solutions perform well when based on scenarios chosen by either a distance-based method or the stratified scenario section method with moment-matched probabilities. In particular, for this application, these methods’ results closely resemble solutions obtained from a much larger model using the full scenario set, and surprisingly have a lower worst case regret. Thus, careful scenario reduction can result in useful models that are more easily solved or, alternatively, can be expanded to accommodate other important features of power systems and markets.
•The uncertainty of modern power systems are illustrated.•The uncertain analysis methods for modern power systems are summarized.•Existing scenario generation, reduction and quality evaluation ...methods are reviewed.•The future research prospects in the scenario analysis methods are discussed.
Addressing the rapidly growing penetration of renewable energy sources and the increasing variations in loads has been a significant challenge in the planning and operation of modern power systems. As effective tools for describing uncertainty issues, scenario analysis methods have been used in the uncertainty evaluation of power systems for years. Substantial work has been conducted in both academia and industry. In this paper, a review of the scenario analysis methods is presented. The progress in scenario generation methods, scenario reduction methods, and scenario quality evaluation indices are surveyed in detail. The new trends of scenario analysis methods are discussed. The present authors consider the scenario analyses of 100% renewable integrated power systems and integrated multiple energy systems as potential research directions.
Abstract
The DIII-D super-H (SH) scenario, which is characterized by a significantly higher pedestal pressure compared to standard high confinement mode (H mode) plasmas, typically exhibits two ...phases in its temporal dynamics. The early hot ion (SH–HI) phase has higher core ion temperatures and normalized confinement factor (
H
98(
y
,2)
∼ 2) than the later ‘standard’ SH phase, which has similar pedestal pressure characteristics to the SH–HI phase but a lower confinement factor (
H
98(
y
,2)
∼ 1.2) as well as lower pedestal
T
i
/
T
e
ratio. However, beyond the pedestal differences, it is also observed that in the core plasma
T
i
is more peaked and has a significantly larger normalized gradient scale length
a
/
L
Ti
in the SH–HI phase than in the SH phase. This paper identifies the physics responsible for the different core profiles via gyrokinetic and gyrofluid modeling. It is found that the ion temperature gradient (ITG) mode dominates the core transport for both phases. Absent flow shear effects, the ITG critical gradient (
a
/
L
Ti,crit
) is shown to be far smaller in the SH–HI phase than the SH phase. The lower
a
/
L
Ti,crit
in the SH–HI phase is shown to be mainly induced by the hollow carbon (impurity) density profile, which is strongly destabilizing relative to the nearly flat carbon density profile in the SH phase. Differences in the
T
i
/
T
e
ratio between these phases are found to have a minor impact. However, the significantly stronger flow shearing in the SH–HI phase relative to the SH phase enables the achievement of higher core
a
/
L
Ti
values and is therefore mainly responsible for the higher core
T
i
values observed in the early SH–HI phase. Predictive transport modeling shows that the confinement in the lower-rotation SH phase could be elevated significantly if a peaked impurity density profile can be achieved, and potential applications to the performance improvement of future reactors are discussed.
Biological invasions have steadily increased over recent centuries. However, we still lack a clear expectation about future trends in alien species numbers. In particular, we do not know whether ...alien species will continue to accumulate in regional floras and faunas, or whether the pace of accumulation will decrease due to the depletion of native source pools. Here, we apply a new model to simulate future numbers of alien species based on estimated sizes of source pools and dynamics of historical invasions, assuming a continuation of processes in the future as observed in the past (a business‐as‐usual scenario). We first validated performance of different model versions by conducting a back‐casting approach, therefore fitting the model to alien species numbers until 1950 and validating predictions on trends from 1950 to 2005. In a second step, we selected the best performing model that provided the most robust predictions to project trajectories of alien species numbers until 2050. Altogether, this resulted in 3,790 stochastic simulation runs for 38 taxon–continent combinations. We provide the first quantitative projections of future trajectories of alien species numbers for seven major taxonomic groups in eight continents, accounting for variation in sampling intensity and uncertainty in projections. Overall, established alien species numbers per continent were predicted to increase from 2005 to 2050 by 36%. Particularly, strong increases were projected for Europe in absolute (+2,543 ± 237 alien species) and relative terms, followed by Temperate Asia (+1,597 ± 197), Northern America (1,484 ± 74) and Southern America (1,391 ± 258). Among individual taxonomic groups, especially strong increases were projected for invertebrates globally. Declining (but still positive) rates were projected only for Australasia. Our projections provide a first baseline for the assessment of future developments of biological invasions, which will help to inform policies to contain the spread of alien species.
The number of alien species has been increasing worldwide, but we still lack clear expectations about future developments of biological invasions. Using a model predicting alien species numbers based on observed developments and species pools, we here provide the first quantitative projections of alien species numbers until 2050 worldwide for a range of taxonomic groups and regions. Our projections show that the rise in alien species numbers will persist to grow with little signs of slowdowns. Overall, the number of alien species is predicted to increase by 36% with particularly steep increases expected for Europe and invertebrates.
•Scenario development can be understood as a valuation practice by which ideas about the future are constructed.•Valuation practices are important for organizations and for fields.•Mechanisms by ...which valuation practices alter relations include commensuration, categorization, narrative, performativity.•By attending to valuation in scenario development, we can be reflexive about what is gained or lost through the process.•We illustrate this in a case for an international elevator and escalator company.•We edit the method drawing on insights from valuation literature, especially the role of narratives.
Scenario development is a core component of foresight practitioners’ and long-term planners’ work. Practices play a critical role in shaping and reifying taken-for-granted structures and ideas, and as such deserve attention. In this paper, we conceptualize scenario building as a practice of valuation. Doing so calls attention to constructive elements and highlights the importance of studying the practice and the field, not only to derive best practices, but to understand how they work and to what potential consequences. We illustrate these ideas with a scenario development consulting project for an international infrastructure company in which we alter the method in three main places: scanning, interim scenario work and scenario development. We demonstrate how conscious attention to the practice can drive subtle shifts in practice and how a ‘valuation lens’ encourages reflexivity about the use of practices.
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