Urban Microclimate Research Articles

From CFD to GIS: a methodology to implement urban microclimate georeferenced databases

The objective of this paper is to present a methodology for the integration of a Computational Fluid Dynamics (CFD) microclimate simulation and a Geographic Information System (GIS). The first workflow involves the attribution of spatial coordinates to the point data extracted from the CFD, the implementation of an SQLite database, and the connection to the database to visualise and use information on environmental and comfort variables. The second workflow involves georeferencing the CFD raster output, attributing an ID to the point data, creating a point grid in a GIS environment, and merging these with the point data on the microclimate. For demonstration purposes, the methodology is tested on a real case study using ENVI-met and ArcGIS Pro.

Optimizing the Surrounding Building Configuration to Improve the Cooling Ability of Urban Parks on Surrounding Neighborhoods

Urban parks reduce air temperatures within parks and surroundings by exerting the cooling island effect, significant for mitigating the urban microclimate. However, the park cooling effect may be influenced by the surrounding building configuration, and this needs to be studied in more detail, in particular, to explore how to maximize the cooling effect of parks by adjusting the surrounding building configuration. Thus, in this study, the effects of building height, building interval, and building orientation on the cooling effect of a small urban park were investigated using field measurements and ENVI-met numerical simulations. The results demonstrated that (1) building height, building interval, and building orientation all impact the park cooling effect, but their impacts vary. (2) Building height had the strongest effect on the park cooling intensity, and adjusting building height provided the maximum park cooling intensity (1.2 °C). (3) Building orientation had the most effect on the park cooling distance, 100 m downwind of the park. (4) The park cooling effect is best when the surrounding buildings were parallel to the prevailing wind direction, and the park cool island has the greatest intensity and range. This study can guide decision-makers in optimizing building configuration to maximize the park cooling effect.

Weather image-based short-term dense wind speed forecast with a ConvLSTM-LSTM deep learning model

Short-term wind speed predication is of great significance for scholars (e.g., understanding wind profiles), practitioners (e.g., building energy management), regulators (e.g., urban microclimate regulation), and even the general public. Current wind speed forecasting methods either generate sparse predictions or occur high cost. This paper reports a novel, inexpensive framework to forecast urban local dense wind speed. The central tenet is a convolutional long short-term memory (ConvLSTM) and LSTM combinatorial deep learning model to learn the features of input historical weather image series coupled with spatial-temporal correlations. The model was trained and tested using Hong Kong datasets. The feasibility and effectiveness of the proposed model are verified and compared with parallel models under different criteria, including mean absolute error (MAE), root mean square error (RMSE) and R-squared (R2). The experimental results show that: (1) the proposed ConvLSTM-LSTM deep learning model can effectively forecast wind speed regardless of location; (2) the overall MAE, RMSE, and R2 value of the proposed model are improved by 14.84%, 15.04%, and 7.51%, respectively, compared to the ConvLSTM-full connected (ConvLSTM-FC) model, and by 22.12%, 22.80%, and 12.24%, respectively, compared to the convolutional neural network-LSTM (CNN-LSTM) model; and (3) compared with parallel models, the proposed model has better performance in predicting wind speed series with large amplitude variations and rapid frequency changes.

Impact of urban surfaces’ solar reflectance on air temperature and radiation flux

This study evaluates the effect of urban surfaces’ solar reflectance on the microclimate of a Brazilian city, Balneário Camboriú. A case study of two different geometrical areas of the city's central region was conducted. The influence of solar reflectance was evaluated through computer simulations on the ENVI-met model, validated for a winter and a spring day, according to field measurements. The simulations were performed for twelve combinations of solar reflectance on the roofs, façades, and pavements. The results confirmed that surfaces of high solar reflectance generally contribute to an air-temperature decrease. However, the degree to which each surface's solar reflectance influences the air temperature depends on the solar access (urban geometry, time, and season). In denser areas, the solar reflectance of facades has a greater impact on temperature variation, whereas in open spaces, roofing and paving surfaces are more critical. Impacts on urban microclimate extend beyond air temperatures. The radiation fluxes on two urban canyons revealed that the solar radiation incidence on the paving of a high solar reflectance canyon could be up to three times greater than one with low reflectance.

Urban agriculture, local economic development and climate change: conceptual linkages

ABSTRACTGlobally, cities have become hubs for economic activity, productivity, and important platforms for achieving sustainable development goals. The potential of urban agriculture (UA) in improving urban local economies and urban micro-climate has been acknowledged in the literature. The study looked at how the concepts of UA, local economic development (LED), and climate change can be treated in unison. Based on the review of credible published papers on the various concepts of UA, LED, climate change and nature-based solutions (NBS), a proposed conceptual framework was developed in this paper showing the linkages. The paper established that UA could boost LED, build resilient urban settlements, and promote social inclusiveness, but with social challenges. It is therefore recommended that policymakers make UA a crucial aspect of their agenda in the coming years to address the local economic and climate challenges now and in the future.

UMC-based models: An integrating UMC performance analysis and numerical methods

Urbanization and climate change represent major public health challenges, impacting several approaches, including urban microclimate (UMC) performance. UMC studies adopt several methods to analyze and mitigate such impacts like numerical methods. Consequently, the current study focuses on UMC performance and associated numerical methods, which can be called UMC-based models. However, the question keeps considering which tool can be used to examine UMC performance, whereas it requires experience. Therefore, this study aims to highlight the guidance of UMC-based models and their possibilities, insights, and opportunities. A bibliometric analysis is conducted based on database development from 1991 to 2022 and both Biblioshiny and VOSviewer tools. The evolution of the yearly publications and prominent bibliometric analyses are explored. The results reveal the continuous evolution of UMC-based models and hotspots related to “urban morphology”, and “vegetation” keywords. However, the categories of “air quality”, “urban ventilation”, and “climate change” present significant topics but need more investigation. Further efforts are needed to develop “UMC modeling” and its associated opportunities related to application fields, in the context of “optimization”, “data-driven”, and “coupled models”, which present trending up and a significant paradigm shift toward UMC performance. Moreover, the proposed matrix provides UMC-based models, and their classifications to outline their possibilities, insights, and opportunities. Such comprehensive results can provide multi-scale opportunities to develop UMC-based models and their application fields, which serves as research guidance to not only select but also develop appropriate and innovative tools or coupled tools associated with UMC performance in response to associated UMC challenges.

High-Resolution Greening Scenarios for Urban Climate Regulation Based on Physical and Socio-Economical Factors

Urban ecosystems represent the main providers of ecosystem services in cities and play a relevant role, among the many services, in the regulation of the urban microclimate and mitigation of the urban heat island effect. The amount, localization, and spatial configuration of vegetation (i.e., urban trees) are key elements for planners and designers aiming at maximizing the climate regulation potential and therefore extending the related benefits to a higher number of residents and city users. Different factors and constraints related to urban morphology and socio-economical characteristics of the urban environment influence the localization of new greening scenarios, therefore impacting the potential benefits that can be obtained by residents. This paper investigates these factors by identifying high-resolution greening scenarios that are able to maximize the cooling benefits for people and local residents. For the case study of metropolitan areas of Catania (Italy) with a hot Mediterranean climate, scenarios are derived by modelling physical and socio-economic factors as spatial constraints with the UMEP model and GIS spatial analysis. Results show that new greenery should be mostly located in public areas that are mostly used by residents. Built on the results obtained in the case study analyzed, the paper also proposes some general planning criteria for the localization of new urban greenery, which should be extended to other geographical urban contexts.

Meteorological modeling of urban “heat islands” on the territory of Belarus under modern global warming

The article presents a quantitative estimation of intensity of urban “heat islands” in Belarus and their changes as a result of global warming. The potential opportunities for improving the urban microclimate by increasing the area of forest park zones in the city have been evaluated using mesoscale numerical simulation of meteorological conditions in cities. It is shown that in summer, Belarusian regional centers are warmer than suburban areas within 2–3 °С during the day and within 1.2–2.3 °С at night. Over the period that has passed since the beginning of this century, the regional cities have warmed by an average of 1.1–2.2 °C during the day and 1.3–1.9 °C at night. The maximum increase in daytime and nighttime temperatures in Belarusian cities has amounted within 3.1–6.0 and 2.4–4.4 °С, respectively. It is shown that replacing industrial clusters with forest park zones decreases the air temperature in the city within 2 °C and more than 2 times in evapotranspiration in the city of Homel. In the daytime, the northwest wind increases in the city and its suburb and this improves urban ventilation. At night, the afforestation of the city makes the surface layer of the atmosphere less stable, which is accompanied by the activation of local circulation cells, through which the temperature and specific humidity in the city and the suburb are smoothed.

The importance of green areas and public spaces for the urban climate and human well-being

urban comfort. The disorderly growth and lack of planning had negative consequences on the environment quality and the well-being of its inhabitants. Reflections and studies have demonstrated the improvement of the environmental quality also come from the green areas, a primordial element in the search for development with new planning practices. This work aims to analyze the literature on the influence of green areas and public open spaces on the environmental and climatological quality of cities, supporting urban microclimate and social well-being. As a methodological basis, a literature review was developed, which included books, articles, theses, and dissertations. After, it was analyzed how the urbanization process of cities and inadequate urban planning directly reflect on environmental comfort. Furthermore, to build an information base about the theme, the investigation of the contributions of green areas and public open spaces in this context was discussed. According to the results found, urban vegetation plays a fundamental role in a healthier built environment for all, and with that, the work helps in future research, and theoretical debates through the realization of this review and contributes to urban landscape projects.

Monitoring of a Living Wall System in Santo Domingo, Dominican Republic, as a Strategy to Reduce the Urban Heat Island

Given the current need to reduce the Urban Heat Island (UHI) worldwide, one of the strategies that can contribute to this mitigation is green façades. In this context, the aim of this research is to evaluate a Living Wall System (LWS) as a strategy to reduce the urban heat island in Santo Domingo, Dominican Republic, using outdoor test cells. This research was focused on the monitoring of two different façades, an LWS and a reference façade, during the warmer months. For the comparison, the parameters measured were air temperature, relative humidity, surface temperature and environmental variables. In addition, thermal images were taken. Results reveal that during the days selected, the average outdoor air temperature difference between the LWS compared to the reference façade was 5.3 °C, whereas during the day, the average was 3.3 °C. Concerning surface temperature, in the case of the LWS, the temperature was higher and had greater fluctuations than the reference façade. This behavior was confirmed by the results obtained with thermal images. In conclusion, using an LWS in a tropical climate helps the urban microclimate, which contributes to urban heat island effect mitigation during the warmer months.

Ice floes in urban furnace: Cooling services of cemeteries in regulating the thermal environment of Istanbul's urban landscape

Cemeteries are supportive parts of the urban green ecosystem due to cooling services that improve urban microclimate. This study aims to provide a quantitative understanding of internal-external cooling effects of cemeteries in Istanbul, high-density metropolitan area suffering from overheating and lack of greenspaces. There are 309 ‘cemeteries’ of diverse shapes and sizes in Istanbul's urban landscape, covered by green elements, impervious surfaces, and water bodies. We conducted a six-stage methodology: sampling design including a taxonomy of patches in super-small/small/medium/large classes; calculation of land surface temperature (LST); determination of cool island intensity and cooling extent; measurements of landscape metrics; Ridge Regression Model iterations; and buffer distance sensitivity analyses in cooling gradients. The research found that cemeteries have remarkable cooling potential, with internal LST between 1.5 and 3 °C below LSTurbanaverage. Cooling efficiency was sensitive to patch size and the building density around the green patches. Even though the influence of patch size on the cooling efficiency was stronger than the landscape patterns, the bigger was not always the better in regulating the thermal environment. Planning super-small/small green patches in high-density centres is a more practical and efficient way to regulate urban neighbourhoods in Istanbul. The study helps professionals for heat mitigation and thermal regulation in the urban environment through green space planning.

Urban microclimate and its impact on built environment – A review

Increasing urbanization and population growth have brought attention to urban microclimates in recent years. The study on urban microclimate and its impact on the built environment is gaining momentum. A growing number of researchers have examined the relationship between human activity and the immediate surroundings to reduce adverse impacts on the environment and climate. This paper presents the latest progress in urban microclimate research on urban wind and thermal environment, covering traditional methods, including field measurements, wind tunnel modeling, and CFD simulations, as well as emerging methods, such as artificial intelligence or data-driven models. Among the publications reviewed, the topics include isothermal scenarios that neglected thermal aspects (e.g., urban wind energy, wind comfort), as well as thermal scenarios (e.g., urban heat islands and outdoor thermal comfort). In the review, it was found that CFD has been widely applied due to its well-developed nature. In addition to field measurements, new techniques (such as satellite and thermal imaging) provide valuable validation data for CFD and training data for artificial intelligence applications. In isothermal scenarios, wind tunnel modeling has been successfully applied. However, thermal scenarios present significant challenges. In addition, urban data-driven models have emerged with promising results, but systematic investigations have been limited. In this paper, we identify future research needs for urban microclimates based on an overview of recent progress.

Urban Microclimate, Outdoor Thermal Comfort, and Socio-Economic Mapping: A Case Study of Philadelphia, PA

Urban areas are often warmer than rural areas due to the phenomenon known as the “urban heat island” (UHI) effect, which can cause discomfort for those engaging in outdoor activities and can have a disproportionate impact on low-income communities, people of color, and the elderly. The intensity of the UHI effect is influenced by a variety of factors, including urban morphology, which can vary from one area to another. To investigate the relationship between outdoor thermal comfort and urban morphology in different urban blocks with varying social vulnerability status, this study developed a geographic information system (GIS)-based workflow that combined the “local climate zone” (LCZ) classification system and an urban microclimate assessment tool called ENVI-met. To demonstrate the effectiveness of this methodology, the study selected two different urban blocks in Philadelphia, Pennsylvania–with high and low social vulnerability indices (SVI)–to compare their microclimate conditions in association with urban morphological characteristics such as green coverage area, sky view factor (SVF), albedo, and street height to width (H/W) ratio. The results of the study showed that there was a strong correlation between tree and grass coverage and outdoor air and mean radiant temperature during hot seasons and extremely hot days, which in turn affected simulated predicted mean vote (PMV). The effects of greenery were more significant in the block associated with a low SVI, where nearly 50% of the site was covered by trees and grass, compared to only 0.02% of the other block associated with a high SVI. Furthermore, the investigation discovered that reduced SVF, along with increased albedo and H/W ratio, had a beneficial impact on the microclimate at the pedestrian level within the two studied urban blocks. This study provided an effective and easy-to-implement method for tackling the inequity issue of outdoor thermal comfort and urban morphology at fine geographic scales.

Envisioning the future—Creating sustainable, healthy and resilient BioCities

Numerous challenges – from population increase to climate change – threaten the sustainable development of cities and call for a fundamental change of urban development and green-blue resource management. Urban forests are vital in this transition, as they provide various ecosystem services and allow to re-shape and re-think cities. Based on a Europe-wide community effort with diverse experts centered around urban forests and urban greening, we propose five key research fields to generate the knowledge required to unlock fundamental changes in urban development and green-blue resource management: circular bioeconomy, climate resilience, governance, social and human environment, and biodiversity. To support the design of greener, cooler, more inclusive and resilient cities, all these research fields require inter- and transdisciplinary collaboration, engaging stakeholders in transforming urban engagement and functioning. We summarise main inter-, trans- und multi-disciplinary research paths for each field and the cross-cutting knowledge areas that can help to address the challenges many cities face (e.g., modelling and assessment of the urban microclimate). For transforming cities further knowledge is needed on e.g., urban innovation, transition, participation, and more. Finally, we address how the identified research gaps can be implemented (e.g., international coordinated research effort, interdisciplinary networks).

A geographic information systems and remote sensing-based approach to assess urban micro-climate change and its impact on human health in Bartin, Turkey.

Increasing land surface temperature (LST) is one of the major urban climatology problems arising in urban development. In this paper, the impact of vegetation and built-up areas on the LST and impact of LST on human health are assessed using the Landsat thermal data in Bartin, Turkey. The results show that there is a constant change in the share of vegetation and built-up areas due to rapid urbanization in Bartin. Strong positive correlation has been found between NDBI and LST while strong negative correlation has been found between NDVI and LST, suggesting their strong impacts on land surface temperatures. Similarly, a strong positive correlation has been observed between LST, sleep deprivation, and heat stress. This study provides precise information on effects of urbanization and man-made activities, which cause major changes in micro-climate and human health in the city. This study can assist decision-makers or planners to plan future developments sustainably.

Numerical Study on the Influence of Rivers on the Urban Microclimate: A Case Study in Chengdu, China

The urban heat island phenomenon in large cities is becoming increasingly serious as urbanization continues to develop, seriously affecting the lives of urban residents. Rivers can effectively alleviate urban heat islands and improve the thermal comfort of riverfront space in summer. Thus, the effect of rivers on the urban microclimate environment is studied in this work. A section of the Fu River in the inland city of Chengdu was selected as the research object, and a combination of experimental and numerical simulation methods was employed. ENVI-met software was used to study the river’s influence on the air temperature, relative air humidity, and the thermal comfort of the riverfront space. The measured experimental parameters are first used to verify the accuracy of the ENVI-met software simulation results, which are then employed to carry out simulation research. The simulation results suggest that the different types of underlying surfaces have varying impacts on the air temperature and relative air humidity. Rivers have a significant cooling effect on the regional thermal environment, and roads have a warming effect on the air temperature. The order of influence of different underlying surfaces on air temperature is as follows: rivers > roads > trees. Rivers have an obvious humidifying effect on the air, and roads have little effect on relative air humidity. The order of influence of different underlying surfaces on relative air humidity is as follows: rivers > trees > roads. The results of the outdoor predicted mean vote (PMV) reveal that rivers, trees, and green plants can effectively improve the comfort of individuals downwind.

Evaluating the Impact of Urban Microclimate on Buildings’ Heating and Cooling Energy Demand Using a Co-Simulation Approach

The current research proposes an integrated computational method to consider the effect of the urban microclimate and the higher urban air temperatures on the assessment of urban building energy demands on an annual basis. A one-way coupling procedure is established to generate datasets on typical weather years that can capture the particularities of the urban microclimate as a function of their morphological and geometrical characteristics, thus providing a global perspective of the annual building energy performance at a reasonable computational cost. The proposed simulation method, here applied for an energy performance analysis of generic, non-insulated building units located in four different urban sites of Thessaloniki, Greece, is based on the three tools: (a) the ENVI-met v.4 microclimate model, (b) the Meteonorm weather generator and (c) the dynamic BEPS tool EnergyPlus. The obtained simulation results indicate a decrease in the annual heating energy needs of the examined building units of 8.2–11.5% when the effect of urban warming was accounted for, along with a rise in the annual cooling energy needs of between 13.4 and 28.2%, depending on the case study area.

Quantitative Evaluation of the Effects of Heat Island on Building Energy Simulation: A Case Study in Wuhan, China

The climate data used for dynamic energy simulation of buildings located in urban regions are usually collected in meteorological stations situated in rural areas, which do not accurately represent the urban microclimate (e.g., urban heat island effect), and this might affect the simulation accuracy. This paper aims at quantitatively evaluating the effects of heat island on a high-rise building’s energy performance based on the microclimate simulation tool ENVI-met and the building energy simulation tool COMFIE. However, the computation of microclimate models is time consuming; it is not possible to simulate every day of a year in a reasonable time. This paper proposes a method that generates hourly “site-specific climate data” to avoid long microclimate simulation times. A coupling method of ENVI-met and COMFIE was developed for more precise building energy simulation, accounting for the heat island effect. It was applied to a high-rise building in Wuhan, China. The results showed that the yearly average urban heat island effect intensity at the height of 3 m was estimated to be 0.55 °C and decreased with height. Compared to the simulation considering the outdoor temperature variation with the height and orientation, using the original climate data collected in rural areas led to an overestimation of the heating load by around 5.8% and an underestimation of the cooling load by around 8.7%. Compared to the weather file at the height of 3 m near the north facade neglecting the temperature variation along the height, the heating load was overestimated by 8.2% and the cooling load was underestimated by 10.8%. The methods proposed in this paper can be used for the more precise application of urban building energy simulation.

Machine Learning-Based Urban Renovation Design for Improving Wind Environment: A Case Study in Xi’an, China

The high-density urban form and building arrangement of modern cities have contributed to numerous environmental problems. The calm wind area caused by inappropriate building arrangements results in pollutant accumulation. To realize a practical design and improve urban microclimate, we investigated the spatial relationship between roads, buildings, and open space using the machine learning technique. First, region growing and k-means clustering were employed to identify roads and buildings. Based on the image masking program, we selected training areas according to the land use map. Second, we used the multiple-point statistics technique to create new urban fabric images. Viewing the training image as a prior model, our program constantly reproduced morphological structures in the target area. We intensified the similarity with training areas and enriched the variability among generated images. Third, Hausdorff distance and multidimensional scaling were applied to achieve a quality examination. The proposed method was performed to fulfill an urban renovation design in Xi’an, China. Based on the historical record, we applied computational fluid dynamics to simulate air circulation and ventilation. The results indicate that the size of calm wind area is reduced. The wind environment is significantly improved due to the rising wind speed.

D-SPARC: Rapid Field Albedo Measurement

The albedo of surfaces in urban areas plays an important role in regulating the urban microclimate and needs to be measured. Artificial urban surfaces, e.g., pavements with lower albedo than natural surfaces such as grass or soil, are a key contributor to the Urban Heat Island (UHI) effect. However, widespread measurement of pavement albedo in the field remains challenging due to limited available daylight hours to record the measurements, the need for clear sky conditions, and slow data collection speed. A new portable system called Discrete SPectrAl RefleCtometer (D-SPARC) was developed to overcome these difficulties. D-SPARC was calibrated in the lab using 25 concrete specimens of known albedo and found to be accurate to within ±0.05, which is similar or better than recently developed aerial or satellite methods. The calibrated D-SPARC device was then used to acquire measurements on ten pavement sections during both the day and night and compared to the results from an albedometer. The RMSE during the day was 0.06 and during the night was 0.02. Each measurement with D-SPARC took about 4 min per test location as compared to 15 min with the albedometer. D-SPARC can be used to conveniently and rapidly measure pavement albedo over a road network with reasonable accuracy and minimal traffic disruption.