Changements globaux

National audienceL'expression " changements globaux " désigne l'ensemble des évolutions qui s'observent à l'échelle de la planète entière. Dans le contexte actuel, le terme fait plus spécifiquement référence aux effets de l'activité humaine sur l'environnement et de ce fait, les changements globaux désignent de nos jours des évolutions tant sociétales qu'environnementales. Par exemple, l'évolution de la démographie ou l'émergence d'un mode de vie urbain généralisé sont des phénomènes sociétaux, alors que le changement climatique ou la perte accélérée de biodiversité relèvent de l'environnement. Si la plupart de ces changements trouvent leur origine dans l'émergence de la société industrielle moderne, certains d'entre eux peuvent être beaucoup plus anciens : la surexploitation des terres et les phénomènes d'érosion, voire de désertification, qui l'accompagnent sont des problématiques multimillénaires. Par ailleurs, les conséquences futures de ces changements s'inscrivent dans le long, voire le très long terme

A Formally and Algorithmically Efficient LULC change Model-Building Environment

The use of spatially explicit land use and land cover (LULC) change models is widespread in environmental sciences and of interest in public decision-help. However, it appears that these models suffer from significant biases and shortcomings, the sources of which can be mathematical, conceptual or algorithmic. We formalize a modeling environment that distinguishes a calibration-estimation module and an allocation module. We propose an accurate calibration-estimation method based on kernel density estimation and detail an unbiased allocation algorithm. Moreover, a method of evaluation of LULC change models is presented and allows us to compare them on various fronts (accuracy, biases, computational efficiency). A case study based on a real land use map but with known (enforced) transition probabilities is used. It appears that the estimation error of the methods we propose is substantially improved over the best existing software. Moreover, these methods require the specification of very few parameters by the user, and are numerically efficient. This article presents an overview of our LULC change modeling framework; its various formal and algorithmic constituents will be detailed in forthcoming papers

A Formally and Algorithmically Efficient LULC change Model-Building Environment

International audienceThe use of spatially explicit land use and land cover (LULC) change models is widespread in environmental sciences and of interest in public decision-help. However, it appears that these models suffer from significant biases and shortcomings, the sources of which can be mathematical, conceptual or algorithmic. We formalize a modeling environment that distinguishes a calibration-estimation module and an allocation module. We propose an accurate calibration-estimation method based on kernel density estimation and detail an unbiased allocation algorithm. Moreover, a method of evaluation of LULC change models is presented and allows us to compare them on various fronts (accuracy, biases, computational efficiency). A case study based on a real land use map but with known (enforced) transition probabilities is used. It appears that the estimation error of the methods we propose is substantially improved over the best existing software. Moreover, these methods require the specification of very few parameters by the user, and are numerically efficient. This article presents an overview of our LULC change modeling framework; its various formal and algorithmic constituents will be detailed in forthcoming papers

Study of cereals flows at local scales: Examples in the Rhône-Alpes région, the Isère département and the SCOT de Grenoble

International audienceThe purpose of this article is to put forward the role applied mathematics and computer science could play in the field of ecological accounting and particularly in that of material flow analysis. It is done based on a detailed study on modeling cereal flows at sub-national scales

Socio-ecological transition, wealth creation and territorial metabolism: the case of the production of the AOC-labelled cheese Beaufort in the Maurienne Valley

International audienc

Modelling for local scale sustainability and decision-making support: reflections and difficulties

International audienceThis paper is about integrated modelling for decision-making support to sustainability policies at local scales. By "local scales" we mean sub-national scales like cities, employment catchment areas, or slightly larger scales like départements and régions, for France. The goal of this article is to share a certain number of our motivations, outlooks and experiences we acquired via the creation of our research group, which tackles this complex topic. In a first step, we identify three scientific domains that we consider to play a key role in local scale sustainability and for which improvement in available knowledge is crucial. In a second part, we discuss challenges and difficulties one is confronted with when one wants to work on the context considered here

Analysing the validity and robustness of the iconic World 3 global model: what can sensitivity and feedback loop analysis say?

International audienc

Dissipative effects on the sustainment of a magnetorotational dynamo in Keplerian shear flow.

The magnetorotational (MRI) dynamo has long been considered one of the possible drivers of turbulent angular momentum transport in astrophysical accretion disks. However, various numerical results suggest that this dynamo may be difficult to excite in the astrophysically relevant regime of magnetic Prandtl number (Pm) significantly smaller than unity, for reasons currently not well understood. The aim of this article is to present the first results of an ongoing numerical investigation of the role of both linear and nonlinear dissipative effects in this problem. Combining a parametric exploration and an energy analysis of incompressible nonlinear MRI dynamo cycles representative of the transitional dynamics in large aspect ratio shearing boxes, we find that turbulent magnetic diffusion makes the excitation and sustainment of this dynamo at moderate magnetic Reynolds number (Rm) increasingly difficult for decreasing Pm. This results in an increase in the critical Rm of the dynamo for increasing kinematic Reynolds number (Re), in agreement with earlier numerical results. Given its very generic nature, we argue that turbulent magnetic diffusion could be an important determinant of MRI dynamo excitation in disks, and may also limit the efficiency of angular momentum transport by MRI turbulence in low Pm regimes