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Lateb M.,New Jersey Institute of Technology | Meroney R.N.,Colorado State University | Yataghene M.,National Research Institute of Science and Technology for Environment and Agriculture | Fellouah H.,Universite de Sherbrooke | And 2 more authors.
Environmental Pollution | Year: 2015

This article deals with the state-of-the-art of experimental and numerical studies carried out regarding air pollutant dispersion in urban environments. Since the simulation of the dispersion field around buildings depends strongly on the correct simulation of the wind-flow structure, the studies performed during the past years on the wind-flow field around buildings are reviewed. This work also identifies errors that can produce poor results when numerically modelling wind flow and dispersion fields around buildings in urban environments. Finally, particular attention is paid to the practical guidelines developed by researchers to establish a common methodology for verification and validation of numerical simulations and/or to assist and support the users for a better implementation of the computational fluid dynamics (CFD) approach. © 2015 Elsevier Ltd. Source

Chetelat J.,MicroGIS Foundation for Spatial Analysis | Kalbermatten M.,Ecole Polytechnique Federale de Lausanne | Lannas K.S.M.,Ecole Polytechnique Federale de Lausanne | Spiegelberger T.,Ecole Polytechnique Federale de Lausanne | And 7 more authors.
Ecology and Society | Year: 2013

This study examines the effects of land-use policies and natural events on the evolution of two wooded pastures in the Jura Mountains in Switzerland between 1934 and 2000. The socioeconomic context and the local conditions were seen as major driving forces influencing land management practices which in turn redefined land-use policies. We studied the dynamics of the Jura Mountains' wooded pastures, combining a thorough knowledge of the historic context with aerial image analysis. Besides pointing out general milestones in the evolution of Swiss land policy, we compiled chronicles on the management for both study sites on the basis of archives and interviews. Aerial images taken at time intervals of approximately 15 years were chosen to identify land-cover changes. The method used to analyze them relied on a structural classification of phytocoenoses, thus allowing the determination of four categories of tree-cover densities ranging from unwooded pastures to ungrazed forest. We reported overall aerial changes for each tree density class as well as spatial transitions from one category to another. The combination of spatial statistics with qualitative data depicting the evolution of the historic context gives a better understanding of the land-use changes and their rationale. The most important changes in tree density occurred during World War II and resulted in a more open landscape. The intensive use of wooded pastures during the war was the consequence of a high demand for wood and food resources. Postwar protectionist regulations, agricultural subsidies, and technical improvements maintained considerable pressure on wooded pastures. Storms and drought episodes further exacerbated this process in some areas. The trend then reversed from the 1970s onwards because of the limitations put on milk production and the falling price of wood. This resulted in a more extensive use of pastures, leading to tree encroachment. However, remote sites were more impacted than pastures closer to inhabited areas, which exhibited a trend towards more segregation between grassland and densely wooded pastures. With both extensification and segregation of land use, the complex vegetation mosaic and the landscape diversity that characterize wooded pastures are threatened but still offer good economic opportunities that call for differentiated management strategies. © 2013 by the author(s). Source

Koech R.,University of New England of Australia | de Camargo A.P.,National Institute of Science and Technology in Irrigation Engineering | Molle B.,National Research Institute of Science and Technology for Environment and Agriculture | Saretta E.,National Institute of Science and Technology in Irrigation Engineering | And 3 more authors.
Journal of Irrigation and Drainage Engineering | Year: 2016

The International Network of Irrigation Testing Laboratories (INITL) undertook a sprinkler intercomparison testing exercise to generate data for an objective comparison of the performances of the different facilities and identify opportunities for further improvements. Three impact sprinklers were tested in four laboratories in accordance with established standards. The plots of flow rate-pressure profiles were found to be consistent, and correlated to those obtained from previous studies. Although there were slight variations in the measured flow rate data, the mean flow rates at each pressure level were the same for the three sprinklers, and the shapes of the radial distribution profiles were similar. The deviations of reconstituted flow rates (from the measured) of at least two tests in each facility were found to exceed the recommended limit. The sprinkler software developed by INITL was found to have a good correlation with a related commercial software program. © 2015 American Society of Civil Engineers. Source

Allouis T.,National Research Institute of Science and Technology for Environment and Agriculture | Durrieu S.,National Research Institute of Science and Technology for Environment and Agriculture | Couteron P.,Institute Of Recherche Pour Le Developpement Botanique Et Bioinformatique
IEEE Geoscience and Remote Sensing Letters | Year: 2012

Forest structure variables, such as the canopy height, are of central interest for the quantification of ecosystem functions and the assessment of biomass levels. The objective of this letter is to propose a new method for ridding canopy-height estimates from the influence of the hillslope within large-footprint (light detection and ranging) LIDAR waveforms. The method is based on modeling (using two generalized Gaussian functions) and the fitting of canopy and ground components to large-footprint (30 m) waveforms. The canopy heights were estimated for 27 waveforms: A root-mean-square error of 3.3 m was obtained using a high-resolution digital terrain model (DTM) to estimate the ground component (4.3 m using the 80-m-resolution Shuttle Radar Topography Mission DTM) and 3.5 m when self-estimating the ground component (hillslope) based on the large-footprint waveform. This approach opens new possibilities for waveform decomposition for natural resources and topography assessments based on large-footprint LIDAR waveforms in forest environments. © 2012 IEEE. Source

Frejaville T.,National Research Institute of Science and Technology for Environment and Agriculture | Frejaville T.,EPHE Paris | Curt T.,National Research Institute of Science and Technology for Environment and Agriculture | Carcaillet C.,EPHE Paris | Carcaillet C.,Institute Of Botanique
Frontiers in Plant Science | Year: 2013

Relationships between the flammability properties of a given plant and its chances of survival after a fire still remain unknown. We hypothesize that the bark flammability of a tree reduces the potential for tree survival following surface fires, and that if tree resistance to fire is provided by a thick insulating bark, the latter must be few flammable. We test, on subalpine tree species, the relationship between the flammability of bark and its insulating ability, identifies the biological traits that determine bark flammability, and assesses their relative susceptibility to surface fires from their bark properties. The experimental set of burning properties was analyzed by Principal Component Analysis to assess the bark flammability. Bark insulating ability was expressed by the critical time to cambium kill computed from bark thickness. Log-linear regressions indicated that bark flammability varies with the bark thickness and the density of wood under bark and that the most flammable barks have poor insulating ability. Susceptibility to surface fires increases from gymnosperm to angiosperm subalpine trees. The co-dominant subalpine species Larix decidua (Mill.) and Pinus cembra (L.) exhibit large differences in both flammability and insulating ability of the bark that should partly explain their contrasted responses to fires in the past. © 2013 Frejaville, Curt and Carcaillet. Source

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