Xenia Stavropulos-Laffaille’s research while affiliated with École Centrale de Nantes and other places

The adaptation of public spaces to episodes of intense heat is now a major challenge for cities. With this in mind, this article presents a contribution aimed at delineating and handling the shadows on the ground or in a horizontal plane at a given height, whether it comes from buildings, street furniture or the tree cover. After a comparison with shadows obtained via two reference tools, we present two urban sites that mix shadows of different origins and, in addition, different indicators. The results of the simulations are compared with pyranometric surveys carried out on site. The aim of these indicators is to assist urban designers with solutions that make it possible to distinguish the respective shadow contributions, their annual evolution and potential spatial or temporal continuities.

Urban designers face the challenge of preserving urban life by creating public spaces that are resilient to rising temperatures. This paper studies the dissemination of urban designs specific to summer (‘urban coolspots’) throughout urban design media. First, the study of an inventory of urban coolspots (182 references) delineates their urban context, the main actors and principal cooling techniques. Second, a typological analysis of the projects’ spatio-climatic set-ups highlights four trends as presented in the media. Finally, this article discusses the contributions of the media to an emerging urban design field and establishing an aesthetic of freshness in public space.

In the context of global warming, cities promote temporary or permanent public space designs based on the integration of various cooling techniques, hereafter called spatio-climatic devices, to locally cool down the atmosphere and preserve urban liveability. Such public spaces create interaction opportunities for citizens to seek thermal pleasure outdoors. To inform about the citizens’ thermal experience of these spaces, this paper explores fieldwork and data analysis methods at the crossroads of urban climatology, environmental psychology and urban design. Four spatio-climatic configurations are investigated in the ‘Extraordinary Garden’ in Nantes (France) through mobile microclimate measurements and ethnographic observations. By applying an ‘urban transect’ approach, preliminary selected microclimate, behavioural and activity observation data is displayed together with spatial information. This allows to highlight thermal situations induced by urban design and to link them to specific citizen-environment interactions. As a result, this approach contributes to a better characterization of urban cool spots as a strategy for more resilient public spaces.

Nature-based solutions (NBS) are increasingly promoted to mitigate urbanization effects, such as the urban heat island. The release of latent heat requires the availability of water in the urban soils. Models able to represent both detailed water and energy budgets are needed for a reliable evaluation of NBSs performances. The TEB-Hydro model is a recent hydro-microclimate model that extends the physics of the urban microclimate model TEB-Veg to water processes in urban subsoil in order to represent more realistically coupled water and energy budgets. Hence, the aim of this paper is to evaluate the TEB-Hydro model regarding how the water processes affect the energy balance. The model is applied to an urban French catchment for which both hydrological and microclimate data are continuously collected. The model shows general good performances in both simulating latent and sensible heat fluxes. Nevertheless, soil water contents are slightly underestimated during wet periods and overestimated during dry periods. Compared to the previous version of the model (TEB-Veg) with a simplified water budget, TEB-Hydro tends to more overestimate latent heat fluxes than TEB-Veg during dry periods. During wet periods, however, TEB-Hydro simulates better sensible heat fluxes and latent heat fluxes.

L'adaptation des villes au changement climatique constitue un enjeu majeur des politiques d’aménagement. Promouvoir l'intégration des infrastructures vertes et bleues dans l'environnement urbain entant que stratégies d'adaptation implique ainsi de comprendre leurs impacts sur les bilans en eau et en énergie. Un modèle hydro microclimatique,TEB-Hydro, a préalablement été développé en tenant compte du couplage détaillé des deux bilans. Cependant, des études récentes ont mis en cause la représentation des processus hydrologiques en sous-sol urbain. Ainsi, ce travail de thèse consiste à améliorer la composante hydrologique du modèle (drainage de l’eau du sol par les réseaux, écoulements souterrains vertical et latéral). Après calage,une évaluation hydrologique est réalisée sur deux bassins versants urbains de Nantes. Dans les deux cas, le calage fait ressortir la même configuration de simulation, malgré des morphologies différentes, ce qui est encourageant pour des applications du modèle en projection climatique. L’évaluation hydrologique met en avant les paramètres clés du modèle et démontre une amélioration du processus de l’infiltration de l’eau du sol dans le réseau d’assainissement. L’évaluation hydro-énergétique du modèle démontre une représentation satisfaisante des flux de chaleur sensible et latente. Le fonctionnement du modèle vis-à-vis de l’évapotranspiration est discuté via le prisme de la végétation et de la morphologie urbaine. Une première application de TEB-Hydro en contexte de changement climatique permet d’évaluer une méthode statistique existante de désagrégation et soulève la problématique de la représentation de la dynamique pluviométrique dans ce contexte.

Climate change and demographic pressures are affecting both the urban water balance and microclimate, thus amplifying urban flooding and the urban heat island phenomena. These issues need to be addressed when engaging in urban planning activities. Local authorities and stakeholders have therefore opted for more nature-based adaptation strategies, which are especially suitable in influencing hydrological and energy processes. Assessing the multiple benefits of such strategies on the urban microclimate requires high-performance numerical tools. This paper presents recent developments dedicated to the water budget in the Town Energy Balance for vegetated surfaces (TEB-Veg) model (surface externalisée; SURFEX v7.3), thus providing a more complete representation of the hydrological processes taking place in the urban subsoil. This new hydrological module is called TEB-Hydro. Its inherent features include the introduction of subsoil beneath built surfaces, the horizontal rebalancing of intra-mesh soil moisture, soil water drainage via the sewer network and the limitation of deep drainage. A sensitivity analysis is then performed in order to identify the hydrological parameters required for model calibration. This new TEB-Hydro model is evaluated on two small residential catchments in Nantes (France), over two distinct periods, by comparing simulated sewer discharge with observed findings. In both cases, the model tends to overestimate total sewer discharge and performs better under wet weather conditions, with a Kling–Gupta efficiency (KGE) statistical criterion greater than 0.80 vs. approximately 0.60 under drier conditions. These results are encouraging since the same set of model parameters is identified for both catchments, irrespective of meteorological and local physical conditions. This approach offers opportunities to apply the TEB-Hydro model at the city scale alongside projections of climate and demographic changes.

Climate change and demographic pressure are common issues to be considered when conducting urban planning. Local authorities and stakeholders have therefore opted for more nature-based adaptation strategies, which are especially suitable to influence both hydrological and energy processes. Assessing the multiple benefits of such strategies on the urban microclimate thus requires effective numerical tools. This paper presents recent developments of the water budget in the TEB-Veg model (SURFEX v7.3), which allows for a better representation of the hydrological processes of urban subsoil. This new hydrological module has been called TEB-Hydro. The developments studied concern the introduction of subsoil underneath built surfaces, and the processes of: horizontally rebalancing intra-mesh soil moisture, draining soil water via the sewer network, and limiting deep drainage in the aim of achieving a more realistic base flow pattern in the sewer system. A sensitivity analysis is then performed in order to identify the hydrological parameters required for model calibration. The new TEB-Hydro model is evaluated on two small residential catchments in Nantes (France) by comparing simulated sewer discharges to observation findings. In both cases, the model tends to overestimate total sewer discharge and performs better under wet climate conditions, with a KGE statistical criterion greater than 0.80 vs. roughly 0.60 under drier weather conditions. Yet these findings remain encouraging since the same set of model parameters are identified for both catchments, irrespective of meteorological and local physical conditions. This approach opens opportunities to apply the model at the city scale with respect to projections of climate and demographic changes.

Cities are confronted to demographic pressure and climate change issues, influencing the life quality, comfort and energy costs. Facing these changes, the understanding of hydrological and energy processes in cities has become essential to future management strategies. However, studies dedicated to urban environment generally represent these processes incompletely, often neglecting the coupling between the water and the energy balance through the process of evapotranspiration. The hydro-microclimate model TEB-Hydro takes this into account explicitly. However, previous studies have shown some defects in the hydrological component of the model. In this context, a sensitivity analysis was conducted on the urban watershed of Rezé (Nantes, France) over a period of 6 years. This site is entirely residential and disposes of a continuous hydrological dataset between 1993 and 1998. Hence, the purpose of this communication is to better understand and to evaluate the connections between different hydrological processes in the urban subsoil in order to improve the hydrological component of the model. First results show a sensitivity of the model to hydrological parameters, describing i) the infiltration rate of surface water through the road structure, ii) the fraction of impermeable surfaces connected to the stormwater sewer, iii) the water-tightness of the sewer pipe iv) the threshold water content to trigger the drainage of soil water by the stormwater sewer, and v) the soil texture.