Urban heat islands and their interactions with air pollution

Project title and acronym: Peri-urban environments: interactions and evolutions in the context of global changes - GaLoP

The GaLoP project is a result of the LabEx call for emerging projects 2016.

Leaders: Erwane Personne (ECOSYS) and Patrick Stella (SADAPT)      Academic partner outside BASC: CNRM (UMR GMME, VILLE team)

The Galop project concerns urban and peri-urban environments and the evaluation of the interactions of these environments with the atmosphere, in particular by taking into account the global changes.

This project was supported to understand and quantify the biophysical interactions between the biosphere, including built-up and artificial spaces, and the atmosphere in terms of energy exchanges (microclimate) and air pollution. Achieving this understanding required elements to assess the impacts of urban sprawl (and its density of artificialization) or the vegetation of urban/artificialized spaces on regional and/or local climate¹.

This work fits in with recent international work on urban heat islands and its interactions with air pollution². Indeed, understanding and assessing the effects of vegetation in cities and its surroundings, whether at the neighborhood scale or at the scale of a conurbation (large or small) is important given the current developments in European cities (urban sprawl and vegetation of conurbations). It is also the case that this specific interaction between vegetated areas, artificial surfaces and the atmosphere has an impact on air quality³.

The diagram opposite illustrates the effects of the presence of vegetation on the urban environment. The surface of vegetation and the structure of the neighborhood are taken into account in the project.  

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In order to answer the questions of these impacts of vegetation as well as of urban sprawl on the urban microclimate, the project has developed a modeling tool to quantify these impacts.

To do this, the TEB model (energy balance model in urban areas⁴) was coupled to the SurfAtm model⁵ which specifies the exchanges of energy and pollutants between vegetation and the atmosphere. The outcome of the coupled BER-SurfAtm model is the necessary lever to study neighborhoods that include vegetated areas.

This first step of modeling is the basis to study the effects of the density of vegetation of the districts on the urban heat islands. Thus, such a tool makes it possible to concretely test the interactions and feedbacks of this or that arrangement of the neighborhoods and to scenario the evolutions of the agglomerations (vegetation, sprawl, urban density, ...).

This preparatory work within the Galop project has contributed to the evaluation of ecosystem services provided by urban farms within the framework of the ADEME SEMOIRS project (internship of Jaime Riano Sanchez, co-supervised by Erwan Personne and Patrick Stella). It has also promoted the launch of a thesis work started in 2019 (thesis S. Le Mentec, funded by the Chaire Lab Environnement-Vinci *, co-supervision by Erwan Personne and Patrick Stella). This work has thus attracted the interest of the Lab Environnement-Vinci Chair and of a large engineering firm (Ingérop) and its environmental department, which supports the interfacing of the coupled model to help justify the revegetation of neighborhoods for which it conducts on-site "environmental" studies.

The perspectives of such a work go beyond the originality of the initial framework which focuses mainly on the microclimate - air quality crossing in a first step. Indeed, in a second time, the widening of the project towards the scenarios of use of surfaces and urban expansion are in the scientific perspectives to be considered. In concrete terms, examining future developments in urban areas and assessing the resulting impacts (microclimates, regional climate and local and regional air quality) are the medium-term objectives of such a scientific investment in these issues.

References 

1. Singh, R., Kalota, D., 2019. Urban Sprawl and Its Impact on Generation of Urban Heat Island: A Case Study of Ludhiana City. Journal of the Indian Society of Remote Sensing 47, 1567–1576. https://doi.org/10.1007/s12524-019-00994-8 

2. Sarrat, C., Lemonsu, A., Masson, V., Guedalia, D., 2006. Impact of urban heat island on regional atmospheric pollution. Atmospheric Environment 40, 1743–1758. https://doi.org/10.1016/j.atmosenv.2005.11.037

3. Fallmann, J., Forkel, R., Emeis, S., 2016. Secondary effects of urban heat island mitigation measures on air quality. Atmospheric Environment 125, 199–211. https://doi.org/10.1016/j.atmosenv.2015.10.094

4. Masson, V., 2000. A Physically-Based Scheme For The Urban Energy Budget In Atmospheric Models. Boundary-Layer Meteorology 94, 357–397. https://doi.org/10.1023/A:1002463829265

5. Personne et al, 2009

Publications 

>Massad, R.S., Lathière, J., Strada, S., Perrin, M., Personne, E., Stéfanon, M., Stella, P., Szopa, S., Noblet-Ducoudré, N. de, 2019. Reviews and syntheses: influences of landscape structure and land uses on local to regional climate and air quality. Biogeosciences 16, 2369–2408. https://doi.org/10.5194/bg-16-2369-2019 (publication commune au projet phare 1 de la première phase du LabEx)

>Stella, P., Petit, C., Sad-Apt, U., Bedos, C., Genermont, S., Loubet, B., Personne, E., Saint-Jean, S., 2016. Les espaces périurbains: entre pollution des villes et pollution des champs aux échelles régionale et locale. The périurbain areas: between pollution from cities and fields at local and regional scales. Pollutions atmosphérique 15. 

>*  THESIS * underway - Sonia Le Mentec – « Atmospheric regulation services provided by vegetation in cities: quantification of building-environment-vegetation interactions using a modeling approach on a neighborhood scale »