VD - Villes Durables 

Rôle du végétal dans le développement urbain durable , une approche par les enjeux liés à la climatologie, l'hydrologie, la maîtrise de l'énergie et les ambiances – VegDUD


<br />VegDUD – Which urban greening?<br />

Which vegetation in the dense city, which impacts?

Urban intensification as a solution against sprawl must be properly organized to produce an acceptable quality of life for city dwellers. The vegetal could be a solution. VegDUD aims at establishing knowledge of vegetation impacts on climate, hydrology, energy consumption, ambiences to orientate policymakers.<br />The studied green set-ups have been selected for their impacts or because they are currently used by planners.<br />To acquire data about vegetation presence in a city, we develop acquisition and processing methods implemented in a Geographical Information System, which also produces city evolution scenarios integrating the green set-ups we intend to assess.<br />To quantify the impacts of these set-ups on the environment, with taking into account the city’s characteristics, two approaches are carried out: the implementation of vegetation into climate, hydrology, building thermal, acoustics models, and in situ and in labo experimentation.<br />The green set-ups assessment is performed at local scale or at urban scale with the help of models and completed by taking into account economical, sensible and use considerations.<br />

Methods and tools developed in the project are:
- Methods dedicated to the analysis of hyper-spectal airborne data and multi-spectral Quickbird images to rapidly produce data about the presence of vegetation in a city with two precision levels: one giving a data detailed by species families at district scale, one less detailed but at city scale;
- A Geographical Information System that integrates the vegetation data at different scales (from the tree to the park) and produces city evolution models.
- Observation methods
- Methods to observe and analyze the microclimate by the way of measures in the air, in the soil and on urban surface;
- Experimentations at reduced-scale;
- Microclimate, hydrology, acoustics, and building thermal models taking into account the green set-ups at scales from the building to the city.
These tools and methods allow us to build the present model of a district of Nantes, to validate the models using the experimental results acquired in this district and then to use the models to assess the impacts of the greening scenarios.

Just beginning the second half of the project, it is still difficult for us to identify the major results.
We have established an experimental data set on a district that is still under study.

The models have strongly progressed and are now able to represent the effects of various vegetation set-ups (trees, lawns, green roofs and walls).

VegDUD project resulted in several scientific publications in conferences on the various areas addressed. In particular, work has already been submitted or are planned in many conferences related to meteorology (HARMO, EMS, ECAM, ICUC), remote sensing (EARSE, IASIM), air flows (PHYSMOD, Coherent flow structures) but also in the field of social sciences (CTHS).

Nowadays, urban sprawl is generating nuisances: the increase of artificial surfaces to the detriment of natural surfaces has consequences on urban environment quality (urban heat island, pollution'), but also on the energy consumption. With the increase of urban population it is necessary to find compromises. In the project VegDUD, vegetation is observed as one of the possible solutions for the sustainable development of cities. - Practices : What are the traditional and novel practices of the urban vegetation ? How interesting are they from the climatic and urban points of view ? How can we formalize the overall (environmental, social, economical) assessment of these practices ? The urban vegetation TYPOLOGIE task group will construct a pluridisciplinary documentation of vegetation set-ups and of their characteristics to answer these first questions. - Instrumentation : Do we know how to quantify the various impacts of vegetation set-ups on the environment ? How much do the increase of artificial surfaces modify these impacts ? What are the best spatial and temporal scales to assess these vegetal techniques ? MODELISATION task group will implement urban vegetation representations in climatology, hydrology, sound propagation, and building energy models. Several scales will be considered, from the architectural scale up to that of the city. It will be completed by an EXPERIMENTATION task group where suited measurement techniques will be implemented to understand the physical processes generated by the vegetation. Experimental campaigns will allow validating the models developed in MODELISATION tasks. - Urban vegetation modeling : What are the techniques allowing to rapidly acquire a sufficient understanding of urban vegetation presence at a large scale ? How can we build numerical models rendering the building-vegetation interactions in the actual city and in the extrapolations of the future city ? How can we construct realistic scenarios allowing to help taking policy decisions or to propose solutions adapted to a sustainable urban development ? To answer this new domain of questions, the PHYSIOGRAPHIE task group will set a GIS based on the typology constructed in the TYPOLOGIE tasks. This GIS will incorporate the new understandings and the alternative scenarios. It will propose simulations and applications to a urban development model including vegetation. Vice versa, it will also allow to integrate and display the simulation results. - Vegetation impact assessment : With which criteria, at which spatial and temporal scales, can we compare the impacts of the various vegetation implantation techniques (vegetal roofs, micro hanging gardens, porous parking lots, filtering roadways, urban lagoons, urban rivers) ? What is the method for an overall assessment ? Can we identify a typo-genealogy of vegetal ambiences in relation with climatic, perceptive, and societal characteristics ? - Retrospective analysis and anticipation : What will be the long term impacts of the actual policies ? What are the possible alternatives ? What is the best vegetation effort with respect to ambience, energy, hydrology stakes ? Can we imagine the urban vegetation as an appropriable space, adapted to the cultural organization of each society ? We will answer these questions in two task groups, EvalPRIV and EvalCOLL, which separate the private use (gardens, architectural set-ups) and the collective use (public gardens, parks) of urban vegetation. In each of these two tasks we will consider the questions of retrospective and prospective analyses. These tasks rely mainly on comparative simulations with the models developed within MODELISATION. The set-ups will be first individually assessed for their small scale impacts, then large scale projections of the most interesting ones will be analyzed. The assessments will not be limited to the physical roles of vegetation, they will integrate the economical constraints, the sensible aspects and the usages of vegetation. Indeed, the sustainable development planning of a vegetation development in an urban site can be isolated neither from the built environment where the citizens will live, nor from the pluri-sensory experience of the users. The final objective of these assessments is to complete the vegetation typology to propose an operational tool allowing to orientate a climatic policy of the urban vegetation.

Project coordination

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.


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