Mexico | EPFL Graph Search

Mexico, officiellement la Ville de Mexico (Ciudad de México , en abrégé CDMX) est une entité fédérative et la capitale du Mexique. Cette entité fédérative n'est ni une ville ni un État au sens des articles 43, 44 et 122 de la Constitution mexicaine. Mexico est un centre financier et culturel important avec une économie agricole très présente dans les périphéries. Fondée au début du par les Mexicas (Aztèques) sur un îlot du lac Texcoco, la ville précolombienne de Tenochtitlan a été remplacée par les conquérants espagnols lors de la chute de l'Empire aztèque en 1521 par la première grande ville de tracé européen du continent. Dès 1522, Hernán Cortés prend la décision de construire au même endroit la capitale de la Nouvelle-Espagne, qu'il nomme « es ». Appelée « district fédéral » (Distrito Federal) avant la , Mexico possède un statut constitutionnel particulier car elle est le siège des pouvoirs de la Nation, et constitue, sans avoir le statut d'État, la entité fédérative du Mexiq

Improvement of an urban turbulence parametrization for meteorological operational forecast and air quality modeling

Clive Muller

During the last century, urban pollution has increased with the growth of cities. Urban air quality has become a high priority as it is directly linked to concerns such as human exposure and health. The present work is dedicated to urban air quality modeling with focus on urban meteorology. The main goal is to improve meteorological and air quality simulations in urban areas. Based on measurements and numerical air quality simulations, Chapter 3 describes the meteorological situation and tests an emission inventory for an ozone pollution episode in Mexico City (2 March 1997), in order to determine the principal factors to be accounted in an air quality study. The Mexico City case shows the great influence of meteorological conditions and pollutant emissions on air quality. A thorough understanding of the phenomena governing the meteorological conditions, like small scale convergence, and an accurate emission inventory validated by VOC measurements in the city, are sensitive elements in an air quality study. In Chapter 4, the presence of an Urban Heat Island (UHI) is underlined over the city of Basel (Switzerland) with the BUBBLE measurements. Further on, the ability of aLMo (the operational weather prediction model of MeteoSwiss) to reproduce the effect of a city on the boundary layer atmospheric flow fields is investigated. Results show that aLMo is not able to reproduce the UHI and hence that its surface scheme based on the Monin-Obukhov Similarity Theory (MOST) is not adapted for the urban areas. Therefore, the Buildings Effects Parametrization (BEP) which has been developed by Martilli et al.(2002) especially for urban areas, is implemented in aLMo. Results show that alMo is now able to reproduce the main behavior of the urban boundary layer as the UHI and BEP has hence a real enhancement potential for aLMo. Chapter 5 shows the sensitivity of aLMo with respect to its vertical resolution. In order to limit the sensitivity of aLMo to the grid resolution, BEP is modified. The mesoscale model furnishes the upper boundary conditions for the inner calculation of BEP. That is, BEP recalculates independently the vertical profiles of wind, temperature and energy based on the surface fluxes of momentum, heat and turbulent kinetic energy. The results obtained show a decrease in the sensitivity to the resolution and a better agreement with the measurements. Furthermore, the modified version of BEP gives additional meteorological fields (temperature, wind and TKE) in the urban canopy. The computed temperature in the urban canopy shows a good agreement with measurements in a Basel street canyon. This work shows that it is not necessary to have a high resolution for taking into account modification of the atmospheric flow fields induced by a city.

EPFL2007

Validation and application of an urban turbulence parameterisation scheme for mesoscale atmospheric models

Yves-Alain F. Roulet

Growing population, extensive use (and abuse) of the natural resources, increasing pollutants emissions in the atmosphere: these are a few obstacles (and not the least) one has to face with nowadays to ensure the sustainability of our planet in general, and of the air quality in particular. In the case of air pollution, the processes that govern the transport and the chemical transformation of pollutants are highly complex and non-linear. The use of numerical models for simulating meteorological fields, which in turn will determine the transport of pollutants in the atmosphere, is thus a very appropriate tool to describe and understand the air pollution problematic. This work focuses on the meteorological simulation, using a mesoscale model. The stress is particularly put on the parameterisation of urban induced effects on the meteorological fields above a city. A detailed urban parameterisation scheme has been implemented in a mesoscale model in a previous work. This new scheme takes into account the presence of a city in a more accurate way as the traditional method usually used in mesoscale models. In the first part of this work, the urban module was validated for a one-dimensional off-line simulation within and above a street canyon in the city of Basel/Switzerland. The simulation results were compared with measurements taken within and above the same street canyon during an intensive observation period in the frame of the BUBBLE project (Basel UrBan Boundary Layer Experiment). The comparison with the measurements and with a simulation using the traditional urban parameterisation showed that the detailed urban scheme improved the quality of the simulation of turbulent fluxes and meteorological parameters (wind, temperature) in the urban canopy. Further on, the mesoscale was applied for a three-dimensional simulation over the city of Basel and its surroundings. The results showed that the model is able to reproduce the wind pattern that prevailed during the simulated episode, and that the accuracy of the temperature simulation in the city is improved with the urban module. In the third part of this work, an air quality study was performed over the Mexico City basin. The mesoscale model simulated the meteorological conditions for the chosen episode (1 and 2 March 1997). The results were then passed to TAPOM, a Eulerian photochemical model that calculates the space and time distribution of air pollutants. The simulated concentrations over the basin showed good agreement with the observed values. The validated model could then be used to test some emissions reduction scenarios for Mexico City. The use of the detailed urban parameterisation scheme for meteorological fields and air pollutants concentration simulation improved the quality of the results in almost all the applied situations. Consequently, the full modelling tool presented and validated in this work can be used for air quality modelling studies over cities and their surroundings.

EPFL2004

Recycler l'eau à Mexico: la station d'épuration, un générateur d'opportunités urbaines

Steffan Heath, Edouard Philippe

Depuis un demi-siècle, Mexico et ses millions d'habitants font face à une surexploitation massive des ressources hydriques locales. L'eau souterraine de l'aquifère, qui constitue la source principale d'approvisionnement en eau de la ville, se trouve dans un état critique d'épuisement résultant de l'extension démesurée de la ville empêchant sa recharge. Afin de réduire le stress actuel sur l'aquifère, la ville doit mieux exploiter les sources d'eau locales à disposition: les eaux usées et pluviales. La création de nouvelles stations d'épuration (STEP) apparait donc comme un enjeu majeur. Cependant, afin de pouvoir projeter une nouvelle STEP dans un tissu urbain dense, il nous semble essentiel de lui donner un nouveau statut, afin que sa présence en ville ne provoque plus un sentiment de rejet, mais représente plutôt une opportunité. En effet, l'énergie ainsi que d'autres produits dérivés résultant du processus de traitement peuvent être bénéfiques à d'autres programmes. Dans le cadre de notre projet, nous proposons donc de combiner la STEP avec une piscine municipale pour démontrer le potentiel de ce principe. Situé à l'Ouest de la ville, le projet est implanté dans une aire dont le tissu urbain recouvre un sol propice à la recharge de l'aquifère. Dans cette zone particulière nommée URA (Urban Recharge Area), se trouve une série de barrages de rétention qui intercepte les rivières, souvent très polluées. En plaçant notre projet en aval de l'un de ces barrages, la STEP génère un corridor vert, où l'eau traitée permet la revitalisation de la rivière jusqu'à son infiltration dans un parc situé 1.5 km en aval. La piscine, preuve urbaine de l'intégration de la STEP, est la première séquence de ce corridor vert.

2012