Assessing the influence of long-term urban growth scenarios on urban climate

International audienceThe objective of this paper is to assess the influence of future urban The objective of this paper is to assess the influence of future urban growth scenarios on future urban climate in Toulouse metropolitan area (France). Specifically, we aim to test the hypothesis that urban growth based on sprawling patterns has a significant influence on the Urban Heat Island (UHI) phenomena than compact patterns. Urban growth simulations, which are based on three contrasting scenarios built by 2100 with respect to different urban patterns, are made using a new spatially explicit urban growth model (SLEUTHR) which is specifically developed for that purpose. Potential UHI maps of 2006 and by 2100 are estimated under the same climate conditions using the SURFEX climate model. The influence of urban form on urban microclimate is assessed by comparing the estimated UHI map of 2006 with the potential UHI maps expected by 2100 with respect to the scenario-based urban expansion maps. Simulations with Meso-NH shows that, for the 2006 experience, the center of Toulouse is warmer than the surrounding rural areas by about 6.4°C at 00 LT and at 06 LT. The results highlight an increase of 1 to 2 degrees in the urban air temperature at the beginning of the night and a lost of cool capacity in the scenarios. Furthermore, the results show that big differences in the scenarios are found when exploring the horizontal distribution of the UHI. The increase in the urbanised surface by 2100 leads to a general elevation of temperatures of about 1°C at 00LT and at 06 LT

Description and validation of a " non path-dependent " model for projecting contrasting urban growth futures

International audienceThis paper presents a model (SLEUTH*) for projecting contrasting urban growth futures.It is derived from the SLEUTH model, which has been modified in order to incorporate an additional spatially explicit factor, and to be used in a fully controlled forecasting mode. Our aim is to spatially allocate urban growth, its amount and pattern, according to predefined prospective scenarios and assuming a non path-dependency approach. This modelling approach aims at being used under a "story and simulation" (SAS) approach, which constrains the model validation. To assess model efficiency, three types of tests have been undertaken: (1) sensitivity tests; (2) reproduction of known changes over a past period; and (3) simulation of changes that break trends. Results show that SLEUTH* conveniently simulates expected urban changes for exploring contrasting scenarios that are the basis for land planning strategies

Characterization of urban heat islands based on the treatment of the urban planning regulations of the French local urban plan

For over 30 years, Urban Heat Island (UHI) have been increasing in intensity, exacerbated by increasing population, urban density and by global warming. These phenomena lead to the emergence of challenges for the life of urban environments: excess mortality and deterioration of comfort conditions, vulnerability of urban networks and infrastructures. French planning policies are institutional tools intended for the governance of urban territories development. With more and more frequent heat episodes, these tools make it possible to manage the evolution of urban morphology and thus anticipate the development of Urban Heat Islands. The impact of urban form on UHI having been attested for many years. As part of a thesis PhD, a methodology is developed to map the sensitivity of urban planning regulations to UHI. This method is being tested in municipalities in the Montpellier Méditerranée metropolitan area. This method is aimed at local authorities and actors of the French territory. It aims to provide a tool and indicators to characterize and anticipate the UHI during the elaboration of French urban planning documents, define issues and guide urban planning policies. The methodology is based on the classification of the urban planning regulations of the French Local Urban Plan (PLU). This urban planning regulation is characterized by a set of articles, which determine urban morphology: land use, architectural characteristics, volume, unbuilt area, etc. Based on this classification, Landsat-8 images are used to determine the Land Surface Temperature (LST) to enrich the classification of the urban planning regulations. By associating the classification of urban planning regulations with temperature treatments, this work allows numerous territorial diagnostic supports: The expected results are relevant for French local authorities. The maps produced will support urban planning documents by making it possible to visualize the vulnerability and behavior of urban morphology and anticipate urban heat islands

The Influence of the Calibration Interval on Simulating Non-Stationary Urban Growth Dynamic Using CA-Markov Model

International audienceThis article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC B

The Influence of the Calibration Interval on Simulating Non-Stationary Urban Growth Dynamic Using CA-Markov Model

The temporal non-stationarity of land use and cover change (LUCC) processes is one of the main sources of uncertainty that may influence the calibration and the validation of spatial path-dependent LUCC models. In relation to that, this research aims to investigate the influence of the temporal non-stationarity of land change on urban growth modeling accuracy based on an empirical approach that uses past LUCC. Accordingly, the urban development in Rennes Metropolitan (France) was simulated using fifteen past calibration intervals which are set from six training dates. The study used Idrisi’s Cellular Automata-Markov model (CA-Markov) which is an inductive pattern-based LUCC software package. The land demand for the simulation year was estimated using the Markov Chain method. Model validation was carried out by assessing the quantity of change, allocation, and spatial patterns accuracy. The quantity disagreement was analyzed by taking into consideration the temporal non-stationarity of change rate over the calibration and the prediction intervals, the model ability to reproduce the past amount of change in the future, and the time duration of the prediction interval. The results show that the calibration interval significantly influenced the amount and the spatial allocation of the estimated change. In addition to that, the spatial allocation of change using CA-Markov depended highly on the basis land cover image rather than the observed transition during the calibration period. Therefore, this study provides useful insights on the role of the training dates in the simulation of non-stationary LUCC

Etalement urbain et évaluation de son impact sur la biodiversité, de la reconstitution des trajectoires à la modélisation prospective. Application à une agglomération de taille moyenne : Rennes Métropole.

Urban sprawl modifies the land cover and the appearance of the countryside, increases threats to peri-urban agriculture, and impacts the environment. It causes disruption of the ecosystems and presents a serious threat to the biodiversity. In the present context of the accelerated increase of urban areas, the study of urban sprawl as well as the assessment and anticipation of its impacts interest both scientists and land managers. The objectives of this thesis is to accurately retrace the evolution of urbanization in Rennes Metropolitan, to appraise its impact on the structure of ecological habitats, and model its evolution under different scenarios in order to assess their consequences on land cover and biodiversity. Therefore, the development of a method to recall the course of land cover changes, based on remote sensing data, is first done. This method evidences the urban sprawl patterns at different scales beginning from the department of Ille-et-Vilaine since 1984 till small sites of some km² since 1952. Then, past and current urban landscapes is characterized using landscape metrics before relating landscape to biological data. Finally, land cover changes have been modelled under different scenarios with a cellular automation in order to evaluate the impacts of each one on land cover and biodiversity. The land cover changes observed from remote sensing data shows a net increase of the urban areas at each of the three considered scales, a decline of forests and green spaces outside the urban tract, a progressive fragmentation of artificial and green surfaces, in addition to a low connectivity of these green areas between the city and the suburbs. The analysis of the relationship between landscape and biological data shows that the urbanization substantially decreases the quantity of species as we move from suburban to urban ranges. It, also, affects but differently the taxa depending on their ability to disperse. The analysis of 2020 land cover projections under different scenarios shows an obvious evolution between 2005 and 2020. However, the difference is low perceptible between land cover scenarios and hence their impacts on biodiversity. These results can be explained by the fact that land cover changes in Rennes Metropolitan are highly constrained by the various planning documents already set, and certainly explained by the model and the accuracy of the data used. Key-words: Urban sprawl, Land cover, Remote Sensing, Object-oriented method, Landscape Metrics, Biodiversity, Modelling, Cellular Automaton, Scenarios.L'étalement urbain modifie l'occupation des sols et la physionomie des campagnes, menace l'agriculture périurbaine, et entraîne des conséquences sur le plan environnemental. Il provoque des perturbations des écosystèmes et constitue une menace sérieuse pour la biodiversité. Dans le contexte actuel d'une artificialisation accélérée des terres, l'étude de l'étalement urbain, l'évaluation et l'anticipation de ses impacts présentent un intérêt tant pour les scientifiques que les gestionnaires du territoire. Les objectifs de cette thèse sont de retracer précisément l'évolution de l'urbanisation sur Rennes Métropole, d'évaluer son impact sur la structuration des habitats écologiques, et de modéliser son évolution selon différents scénarios afin d'évaluer leurs conséquences sur l'occupation des sols et sur la biodiversité. Pour cela, une méthode de reconstitution des trajectoires d'occupation et d'utilisation des sols a d'abord été développée à partir de données de télédétection afin de mettre en évidence l'extension urbaine et de l'analyser à différentes échelles, allant du département d'Ille-et-Vilaine depuis vingt ans à de petits sites de quelques km² depuis les années 50. Ensuite, les paysages urbains actuels et passés ont été caractérisés à l'aide d'indicateurs relevant de l'écologie du paysage, avant de mettre ces derniers en relation avec des données biologiques. Enfin, les changements d'occupation du sol ont été modélisés selon différents scénarios avec un modèle intégrant un automate cellulaire, afin d'évaluer les impacts des scénarios sur les changements d'usage des sols et des paysages et sur la biodiversité. L'analyse des changements d'occupation du sol observés par télédétection illustre une nette progression du tissu urbain aux trois échelles étudiées, une régression des forêts et espaces verts à l'extérieur de la tache urbaine contre une augmentation à l'intérieur de cette tache, une fragmentation progressive des surfaces artificialisées et des espaces verts, une faible connectivité des espaces verts entre la ville et la périphérie. La mise en relation des données paysagères avec les données biologiques montre qu'au niveau des végétaux, l'urbanisation affecte le nombre d'espèces qui diminue sensiblement en allant du périurbain vers l'urbain. Au niveau des animaux, les résultats montrent que l'urbanisation affecte différemment les taxons en fonction de leur capacité de dispersion. L'analyse de l'occupation des sols projetée à un horizon 2020 selon différents scénarios montre que l'évolution 2005-2020 est très marquée, mais que les différences d'occupation des sols entre les scénarios et donc leurs impacts sur la biodiversité sont à peine perceptibles d'un scénario à l'autre. Ceci peut s'expliquer par le fait que l'évolution des surfaces urbanisées à Rennes Métropole est très contrainte par les différents documents de planification déjà existants, mais sans doute aussi par le modèle et la précision des données qu'il utilise. Mots-clés : Etalement urbain, Occupation des sols, Télédétection, Méthode Orientée-objet, Indices paysagers, Biodiversité, Modélisation, Automate cellulaire, Scénarios

Suivi de l’artificialisation du territoire en milieu urbain par télédétection et à l’aide de métriques paysagères. Application à une agglomération de taille moyenne, Rennes Métropole

The objective of this research is to explore the combined application of remote sensing and landscape metrics in order to analyze and monitor urban growth in Rennes Metropolitan Area (France). The investigation is based on a 21-year time series data set compiled from Landsat imagery between 1984 and 2005. First, land use and land cover changes were analyzed based on the classification of satellite images using an object-oriented approach. Second, spatial metrics were used to analyze the main spatial and temporal dynamics of urban growth, and to assess its impact on landscape. The results reveal a significant increase in developed areas, which are unevenly distributed over space and time. Such increase with an average annual rate of 190 ha/an is mainly due to the conversion of agricultural lands into urbanized areas, while green and wooded areas continue to increase within new developed areas. The analysis of spatial metrics illustrates how urban expansion in Rennes Metropolitan area has changed from an outlying fragmentation of landscape to an edge-expansion growth