UNCERTAINTY QUANTIFICATION ON A REAL CASE WITH TELEMAC-2D

Water Qualit

Reduced order models based on local POD plus Galerkin projection

A method is presented to accelerate numerical simulations on parabolic problems using a numerical code and a Galerkin system (obtained via POD plus Galerkin projection) on a sequence of interspersed intervals. The lengths of these intervals are chosen according to several basic ideas that include an a priori estimate of the error of the Galerkin approximation. Several improvements are introduced that reduce computational complexity and deal with: (a) updating the POD manifold (instead of calculating it) at the end of each Galerkin interval; (b) using only a limited number of mesh points to calculate the right hand side of the Galerkin system; and (c) introducing a second error estimate based on a second Galerkin system to account for situations in which qualitative changes in the dynamics occur during the application of the Galerkin system. The resulting method, called local POD plus Galerkin projection method, turns out to be both robust and efficient. For illustration, we consider a time-dependent Fisher-like equation and a complex Ginzburg–Landau equation

Global Tipping Points Report 2023: Ch1.5: Climate tipping point interactions and cascades.

This chapter reviews interactions between climate tipping systems and assesses the potential risk of cascading effects. After a definition of tipping system interactions, we map out the current state of the literature on specific interactions between climate tipping systems that may be important for the overall stability of the climate system. For this, we gather evidence from model simulations, observations and conceptual understanding, as well as archetypal examples of palaeoclimate reconstructions where propagating transitions were potentially at play. This chapter concludes by identifying crucial knowledge gaps in tipping system interactions that should be resolved in order to improve risk assessments of cascading transitions under future climate change scenarios

Climate tipping point interactions and cascades: A review

Climate tipping elements are large-scale subsystems of the Earth that may transgress critical thresholds (tipping points) under ongoing global warming, with substantial impacts on the biosphere and human societies. Frequently studied examples of such tipping elements include the Greenland Ice Sheet, the Atlantic Meridional Overturning Circulation (AMOC), permafrost, monsoon systems, and the Amazon rainforest. While recent scientific efforts have improved our knowledge about individual tipping elements, the interactions between them are less well understood. Also, the potential of individual tipping events to induce additional tipping elsewhere or stabilize other tipping elements is largely unknown. Here, we map out the current state of the literature on the interactions between climate tipping elements and review the influences between them. To do so, we gathered evidence from model simulations, observations, and conceptual understanding, as well as examples of paleoclimate reconstructions where multi-component or spatially propagating transitions were potentially at play. While uncertainties are large, we find indications that many of the interactions between tipping elements are destabilizing. Therefore, we conclude that tipping elements should not only be studied in isolation, but also more emphasis has to be put on potential interactions. This means that tipping cascades cannot be ruled out on centennial to millennial timescales at global warming levels between 1.5 and 2.0 ◦C or on shorter timescales if global warming surpassed 2.0 ◦C. At these higher levels of global warming, tipping cascades may then include fast tipping elements such as the AMOC or the Amazon rainforest. To address crucial knowledge gaps in tipping element interactions, we propose four strategies combining observation-based approaches, Earth system modeling expertise, computational advances, and expert knowledge

Gardens of happiness: Sir William Temple, temperance and China

This is the author accepted manuscript. The final version is available from Taylor & Francis via the DOI in this recordSir William Temple, an English statesman and humanist, wrote “Upon the Gardens of Epicurus” in 1685, taking a neo-epicurean approach to happiness and temperance. In accord with Pierre Gassendi’s epicureanism, “happiness” is characterised as freedom from disturbance and pain in mind and body, whereas “temperance” means following nature (Providence and one’s physiopsychological constitution). For Temple, cultivating fruit trees in his garden was analogous to the threefold cultivation of temperance as a virtue in the humoral body (as food), the mind (as freedom from the passions), and the bodyeconomic (as circulating goods) in order to attain happiness. A regimen that was supposed to cure the malaise of Restoration amidst a crisis of unbridled passions, this threefold cultivation of temperance underlines Temple’s reception of China and Confucianism wherein happiness and temperance are highlighted. Thus Temple’s “gardens of happiness” represent not only a reinterpretation of classical ideas, but also his dialogue with China.European CommissionLeverhulme Trus

Inversion probabiliste en analyse d'incertitude.

International audienceno abstrac

uncertainty in the parameters of a risk model

Hierarchical propagation of probabilistic and non-probabilisti

Detecting outlying simulations in BEPU appraoches

International audienceNuclear safety studies, based on the so-called BEPU (Best Estimate Plus Uncertainty) approaches, aim to calculate not only the possible values of a physical variable of interest, but also to quantify its associated uncertainty. From the results of a BEPU study, statistical analysis tools aim to improve the understanding of the physical phenomena simulated by the computer codes. The data outputs generated by these codes typically possess a functional nature, i.e. they represent the temporal evolution of a physical parameter throughout a transient. However, this functional nature is not always taken into account, in spite of the fact that it may provide relevant information regarding nuclear safety. On top of that, the functional analysisof data is even more relevant for transients where the safety criteria is directly associated to the dynamic behavior of a physical parameter, as it is in the case of the pressurized thermal shock. This work addresses the automatic identification of atypical transients (called “outliers”) in sets of time-dependent simulations that can help to better detect the physical phenomena that influence the safety margins, to find penalizing scenarios, or to verify the physical consistency of industrial simulators. A new functional outlier detection technique is then presented, as well as the eventual statistical link between the outlying simulations and the inputs of the computer code. The relevance of this methodology is illustrated on pressurized thermal shock simulations