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Highlights • We propose a parametric model dedicated to urban soil thermal modeling. • A combination of two reduced-order methods, i.e. POD and PGD, is presented. • Calculated temperatures are evaluated with respect to in situ measurements. • The parametric soil model is coupled with the SOLENE-microclimat tool. • Its accuracy and computational cost are evaluated in an urban setting. Abstract Numerical simulation is a powerful tool for assessing the causes of an Urban Heat Island (UHI) effect or quantifying the impact of mitigation solutions on local climatic conditions. However, the numerical cost associated with such a tool is quite significant at the scale of an entire district. Today, the main challenge consists of achieving both a proper representation of the physical phenomena and a critical reduction in the numerical costs of running simulations. This paper presents a combined parametric urban soil model that accurately reproduces thermal heat flux exchanges between the soil and the urban environment with a reduced computational time. For this purpose, the use of a combination of two reduced-order methods is proposed herein: the Proper Orthogonal Decomposition method, and the Proper Generalized Decomposition method. The developed model is applied to two case studies in order to establish a practical evaluation: an open area independent of the influences of the surrounding surface, and a theoretical urban scene with two canyon streets. The error due to the model reduction remains below 0.2 °C on the mean surface temperature for a reduced computational cost of 80%. Compared to in situ measurements the error remains bellow 1.24 °C at the surface. [ABSTRACT FROM AUTHOR]

Urban air temperature varies along time and space. This contribution proposes a methodology to model these variations from empirical models. Four air temperature networks are implemented in three west France cities. The period [1.4–1.8] of a normalized night is investigated. Three empirical models are established, in order to predict temporal and spatial air temperature variation. They are gathered under the name of model group . Urban heat island (UHI) intensity is explained according to one temporal model using meteorological variables. Temperature spatial variations are explained from two models using geographical informations averaged in a 500 m radius buffer circle. The first one represents the mean UHI value for a given location, the second the variability of the UHI around its mean value. 32 model groups are calibrated from data sampled by one network. The accuracy of their estimations is tested comparing estimated to observed values from the three other networks. The most accurate model is identified and its performances are analyzed. Night-time UHI intensity variations are explained all along the year by wind speed and nebulosity values calculated after sunset. During spring and summer season UHI variations are mainly driven by Normalized Difference Vegetation Index (NDVI) value whereas building density or surface density are predominant explicative variables during colder seasons. The model is finally applied to the city of Nantes during a summer night to illustrate the interest of this work to urban planning applications. Several warm areas located outside the city center are identified according to this method. Their high UHI value is mainly caused by their low NDVI value. [ABSTRACT FROM AUTHOR]

A lot of geographers, scientists believe that the current climate has changed. Especially, since the rapid increment of world's population. Indeed, rapid urbanization led to an increased demand of basic facilities, such as public transport services, hospitals, housing &, etc. Accordingly; the urban areas of cities have been expanded compared to rural areas, and many modifications and changes have been happened on their surface's materials. These modifications made our cities hotter than the Countryside, UHI effect phenomenon now well-known. One of the main reasons behind these changes is construction materials in both buildings and urban spaces, which play a major role in affecting the urban temperatures, precisely near-surface air temperatures positively or negatively, which depend mainly on the behaviour of the surface with solar radiation and how the energy is reflected, emitted, and absorbed. Thus, the current study aimed to investigate the direct and indirect impacts of materials reflection coefficient on the environmental performance and external urban surface temperature; by using the SOLENE-microclimate model tool (developed by the laboratory CRENAU - ENSA Nantes); which is a direct effect on external air temperature in terms of sustainability in the urban context. This study applied on one of the most important residential complexes in Mosul city - Iraq as a case study. The results were proved that when used a material with high reflectivity; Comparing low albedo Scenario(1) with high albedo Scenario(3); it can improve the thermal behaviour of building and urban surfaces, where the surfaces temperature of rooftop, walls, urban spaces, road have been changed by, respectively, 25°C, 18°C, 20°C, and 18°C. As well as changed the urban air temperature by 11°C. However, the results showed that in some cases the surface temperatures increased slightly even when reflectivity increased in the scene, (comparison scenario 3 and scenario 5) where the change of albedo value of external walls surfaces have affected increasing the average urban spaces & pavement temperature about 2°C. The tool that is used in this study (SOLENE-microclimate) has effectively helped in achieving all the analysis required successfully, which it represent the most specialized tool in this field. [ABSTRACT FROM AUTHOR]

The urban population rise leads town planners to increase the building density in order to avoid an urban sprawl what can induce higher risks of the heat island occurrence and increases buildings needs for air conditioning. Urban vegetation such as trees, grass areas, green walls and roofs can be a solution to mitigate it. The aim of the study is to evaluate the influence of various greenery types on cooling needs and to classify them according to their ability to mitigate it. Numerical simulations were carried out for canyon street configurations. The 3D numerical tool takes into account the unsteady building thermal behaviour using the SOLENE thermo-radiative model coupled with the outside airflow computed with the CFD tool Code_Saturne. A parametric modelling study considering different kinds of buildings permits to identify the most efficient greenery types and to investigate the interactions between each of them. Green walls and trees appear as the most efficient to reduce cooling needs. The less insulated and the more glassed the buildings are, the more efficient these devices are. The impact of grass areas and green walls applied on neighbouring buildings is only sensible without trees in the street and green cover on the studied building. [ABSTRACT FROM AUTHOR]

Urban shape determines the absorption and emission of radiation. Urban fabrics are characterized by the solar trapping effect due to multiple reflections of radiation within the geometry, in turn generating increased energy absorption that contributes to the urban heat island. Interactions between urban radiative properties and urban shape are studied through an analytical development. A simplified solar balance model is developed based on morphological indicators. A processing chain is performed within OrbisGIS Geographic Information System (GIS) to characterize urban shapes from geographic data supplied by the French IGN. The studied territories are partitioned from the road network into elementary areas of city blocks. The processing chain also includes the production of 3D block models that are used in the SOLENE solar simulation model to perform detailed radiative simulations. The incident and absorbed solar radiations are estimated on 440 actual city blocks from the simplified solar balance model and then compared to the SOLENE computations. The relationships between the simplified solar balance model and the SOLENE simulations are investigated using linear regression analysis. The comparisons show significant correlations and that the simplified solar balance model developed is consistent with the simulations. This contribution produces simple and accurate radiative parametrizations that can be used in urban microclimate models to represent solar trapping and to evaluate radiation availability. [ABSTRACT FROM AUTHOR]

Expected Global warming and heatwaves coupled with the urban heat island effect (UHI) can overheat indoor environments of free-floating buildings in temperate climate regions. Overheating assessment requires practitioners to use appropriate climate data and suitable measurement indices. The aim of this article is first, to propose a practical approach to generate yearly and typical ready-to-use future typical weather datasets (FTWY) using high-resolution Regional Climate Model (RCM) data from Coordinated Regional Climate Downscaling Experiment (CORDEX), and second, investigate the potential of FTWYs in the assessment of indoor overheating, considering UHI effect. To achieve these objectives, three dynamically downscaled (DDS) FTWYs generated from RCMs (IPSL-SMHI, CNRM-ALADIN, MPI-REMO) were compared with one statistically downscaled (ESD) FTWY from Meteonorm, and observed heatwave weather data of 2003. Comparative analysis was performed in two stages: comparison of monthly statistical distribution of climate variables, and analysis of heatwave presence. Urban weather generator (UWG) was used to project UHI effect on two weather files for two buildings, and three overheating measurement indices were used to exploit results. Comparative analysis of weather files show that temperature in a FTWY in the medium future (2040–2070) is likely not as intense as the heatwave of 2003 for Nantes. Results also confirm that it is better to use two weather files, and at least two overheating indices to obtain reliable outputs. This study also revealed that indoor overheating is not limited to densely built areas where impact of UHI is highest; buildings located in sparsely built neighbourhoods are also at risk. [Display omitted] • A practical workflow to construct yearly and typical weather files from EURO-CORDEX is presented. • Contrary to assumptions, medium future typical years are not as intense as 2003 heatwave year in Nantes. • Buildings located in sparsely built locations that are less affected by UHI are also at risk of overheating. [ABSTRACT FROM AUTHOR]

The urban context is often simplified or neglected in Building Energy Models (BEMs) due to the difficulties of taking accurately into account all the heat fluxes emanating from the environment. Oversimplifying the urban context can impact the accuracy of the BEM predictions. Nevertheless, several approaches can be used to allow for the impact of the urban environment on the dynamic behavior of a building, its heating and cooling demands, and thermal comfort. This state of the art review provides a critical overview of the different methods currently used to take into account the urban microclimate in building design simulations. First, both the microclimate and building models are presented, focusing on their assumptions and capabilities. Second, a few examples of coupling, performed between both modeling scales are analyzed. Last, the discussion highlights the differences obtained between simulations that take the urban context into consideration and those that simplify or neglect urban heat fluxes. The remaining scientific obstacles to a more effective consideration of the urban context impacting the BEMs are indicated. • The local data produced by a selection of urban climate models (UCMs) are presented. • An analysis of how the urban context is taken into account in building energy models (BEMs) is given. • Several chaining or coupling strategies to link UCMs and BEMs are analyzed and compared. • Using local climate data leads to a noticeable impact on the thermal behavior of buildings. • Recommendations for better consideration of the urban context in BEMs are formulated. [ABSTRACT FROM AUTHOR]

Since some years, dense cities and compact buildings are promoted as sustainable and energy efficient designs. Nevertheless, urban planning strategies should take into account the interactions between buildings and the microclimate because the Urban Heat Island (UHI) phenomenon can increase the cooling load of buildings and is strongly influenced by urban morphology, urban landscaping and the thermal properties of buildings and soil. The modification of these parameters, such as building density, can mitigate UHI, with direct and indirect improvement of building energy performances. The case study presented in this paper concerns a new district in La Rochelle (France) named Atlantech. Currently at the design stage, the goal is to transform this old military camp into a zero carbon district. This study was performed in parallel with urban planning using EnviBatE and SOLENE-Microclimate simulation. Two building densities are compared through the impacts on solar irradiance, wind airflows, building indoor temperatures and energy demand. Analysis of reference and densified district highlights various impacts such as the wind velocity decrease, up to 80%, and the effect on an existing nearby building solar irradiation, reduced by 7%. These results underline the potential usefulness of these simulation tools for urban planners at the design stage. [ABSTRACT FROM AUTHOR]

• An evaluation toolbox to consider nature-based solutions in urban areas is settled. • Impact of nature-based solutions depends on urban environmental challenges. • A decision-support methodology considering soil-water-climate aspects is developed. • Several indicators were determined and compared to define the toolbox. In the context of climate change, Nature-Based Solutions (NBSs), a recently developed concept, are increasingly considered as part of the adaptation strategies of the cities. Studies using expert models and methods (EMM) receive a great deal of scientific attention. Considering EMM increasing use, this study aims to perform an analysis of the reported evaluation results, reflecting the capability of the EMM to accurately tackle urban challenges identified within the EU Nature4Cities project. Then, we propose a set of indicators and recommendations about sixteen EMM to be used by funders, researchers and practitioners when evaluating the performance of NBSs. The coupling of the different components (climate, water and soil) is not a simple matter. The analysis relies on the definition of the range of the reported metrics and on the investigation of the relationship between the various indices, applied for the EMM evaluation. Secondly, the study assesses the existing EMM, indicating the potential of NBSs: (i) to reduce urban heat island, (ii) to limit surface warming, (iii) to increase the thermal comfort of people, (iv) to limit the overheating and runoff of surfaces due to impervious areas, (v) to increase water retention during stormy episodes, (vi) to improve storm water quality at the outlet of the sustainable urban drainage systems, (vii) to promote the filtration and epuration of storm water runoff in soil and (viii) to be a support for vegetation. The analysis reveals that EMM can be considered as helpful tools for urban microclimate, urban soil and water management analysis, provided their limitations and characteristics are taken into account by the user when choosing tools and interpreting results (e.g. application scale). With regard to the performance of NBSs, the most commonly used indicators clearly depend on the scale of the project. [ABSTRACT FROM AUTHOR]