Climate and more sustainable cities: climate information for improved planning and management of cities (producers/capabilities perspective)

In the last two decades substantial advances have been made in the understanding of the scientific basis of urban climates. These are reviewed here with attention to sustainability of cities, applications that use climate information, and scientific understanding in relation to measurements and modelling. Consideration is given from street (micro) scale to neighbourhood (local) to city and region (meso) scale. Those areas where improvements are needed in the next decade to ensure more sustainable cities are identified. High-priority recommendations are made in the following six strategic areas: observations, data, understanding, modelling, tools and education. These include the need for more operational urban measurement stations and networks; for an international data archive to aid translation of research findings into design tools, along with guidelines for different climate zones and land uses; to develop methods to analyse atmospheric data measured above complex urban surfaces; to improve short-range, high-resolution numerical prediction of weather, air quality and chemical dispersion through improved modelling of the biogeophysical features of the urban land surface; to improve education about urban meteorology; and to encourage communication across scientific disciplines at a range of spatial and temporal scales

Autonomous 3D Urban and Complex Terrain Geometry Generation and Micro-Climate Modelling Using CFD and Deep Learning

Sustainable building design requires a clear understanding and realistic modelling of the complex interaction between climate and built environment to create safe and comfortable outdoor and indoor spaces. This necessitates unprecedented urban climate modelling at high temporal and spatial resolution. The interaction between complex urban geometries and the microclimate is characterized by complex transport mechanisms. The challenge to generate geometric and physics boundary conditions in an automated manner is hindering the progress of computational methods in urban design. Thus, the challenge of modelling realistic and pragmatic numerical urban micro-climate for wind engineering, environmental, and building energy simulation applications should address the complexity of the geometry and the variability of surface types involved in urban exposures. The original contribution to knowledge in this research is the proposed an end-to-end workflow that employs a cutting-edge deep learning model for image segmentation to generate building footprint polygons autonomously and combining those polygons with LiDAR data to generate level of detail three (LOD3) 3D building models to tackle the geometry modelling issue in climate modelling and solar power potential assessment. Urban and topography geometric modelling is a challenging task when undertaking climate model assessment. This paper describes a deep learning technique that is based on U-Net architecture to automate 3D building model generation by combining satellite imagery with LiDAR data. The deep learning model used registered a mean squared error of 0.02. The extracted building polygons were extruded using height information from corresponding LiDAR data. The building roof structures were also modelled from the same point cloud data. The method used has the potential to automate the task of generating urban scale 3D building models and can be used for city-wide applications. The advantage of applying a deep learning model in an image processing task is that it can be applied to a new set of input image data to extract building footprint polygons for autonomous application once it has been trained. In addition, the model can be improved over time with minimum adjustments when an improved quality dataset is available, and the trained parameters can be improved further building on previously learned features. Application examples for pedestrian level wind and solar energy availability assessment as well as modeling wind flow over complex terrain are presented

Confronting Grand Challenges in environmental fluid mechanics

Environmental fluid mechanics underlies a wealth of natural, industrial and, by extension, societal challenges. In the coming decades, as we strive towards a more sustainable planet, there are a wide range of grand challenge problems that need to be tackled, ranging from fundamental advances in understanding and modeling of stratified turbulence and consequent mixing, to applied studies of pollution transport in the ocean, atmosphere and urban environments. A workshop was organized in the Les Houches School of Physics in France in January 2019 with the objective of gathering leading figures in the field to produce a road map for the scientific community. Five subject areas were addressed: multiphase flow, stratified flow, ocean transport, atmospheric and urban transport, and weather and climate prediction. This article summarizes the discussions and outcomes of the meeting, with the intent of providing a resource for the community going forward

Systematic Simulation Method to Quantify and Control Pedestrian Comfort and Exposure during Urban Heat Island

An urban heat island (UHI) originates with the increase of energy consumption and deforestation within urban areas. In addition to heat related illness and energy consumption increase, the UHI also has a mutual effect on pollution dispersion, mostly emitted from vehicular and industrial sources. Many cities recently started to apply mitigation protocols by increasing tree planting and vegetation inside urban areas. A few cities also promoted higher-albedo materials for urban surfaces. Moreover, guidelines are developed to design an appropriate street canyon and building layout to naturally ventilate urban areas. However, the UHI intensity varies in different street canyons and climates. Thus, the aforementioned mitigation technologies are not always practical or economical to reduce energy consumption and keep pedestrian comfort and exposure (PCE) in the desired range. The main goal of this research is to propose a systematic approach, PCE-algorithm, to quantify the level of PCE inside a street canyon before and after its construction. This approach is also capable of evaluating the possible advantages of passive mitigation strategies using a frequency of occurrence concept. This concept assesses the probability iv of having acceptable comfort indices within the street canyon. For this purpose, a computational fluid dynamics (CFD) model is defined around the investigated street canyon. This model simulates the significant contributing parameters on UHI formation, including solar radiation, storage heat, latent heat, and sensible heat. Moreover, an adaptive novel strategy, pedestrian ventilation system (PVS), is proposed in this research to control PCE of the target street canyon. Similar to the function of a building mechanical ventilation system, the PVS interactively controls PCE in outdoor spaces. The PVS employs exhausting and/or supplying fans installed in adjacent buildings of the street canyon in order to achieve an acceptable PCE, especially when passive strategies fail to have a considerable effect. A case study of a street canyon, located in Montreal, is also considered to investigate the performance of the proposed algorithm. After an evaluation of PCE, the effect of the passive mitigation strategies is investigated. Furthermore, it is shown that the PVS can control and improve PCE, especially where severe UHI occurs

Development of a new urban climate model based on the model PALM – Project overview, planned work, and first achievements

In this article we outline the model development planned within the joint project Model-based city planning and application in climate change (MOSAIK). The MOSAIK project is funded by the German Federal Ministry of Education and Research (BMBF) within the framework Urban Climate Under Change ([UC]2) since 2016. The aim of MOSAIK is to develop a highly-efficient, modern, and high-resolution urban climate model that allows to be applied for building-resolving simulations of large cities such as Berlin (Germany). The new urban climate model will be based on the well-established large-eddy simulation code PALM, which already has numerous features related to this goal, such as an option for prescribing Cartesian obstacles. In this article we will outline those components that will be added or modified in the framework of MOSAIK. Moreover, we will discuss the everlasting issue of acquisition of suitable geographical information as input data and the underlying requirements from the model’s perspective

Contribution to the Exposure Assessment for the Evaluation of Wind Effects on Buildings

Contribution to the Exposure Assessment for the Evaluation of Wind Effects on Buildings Jianhan Yu, Ph.D. Concordia University, 2022 The upstream exposure has a major influence on wind loading and on wind environmental conditions around buildings. However, exposure characterization is also a complex and difficult wind engineering problem. The present comprehensive investigation addresses the exposure assessment issue in terms of evaluating the exposure roughness length (zo) by using various computational approaches. Countries specify exposure coefficients in wind load provisions to help designers evaluate wind loads on buildings. However, these specifications can include inconsistencies and discrepancies, leading to different results for similar cases while the wind characteristics do not change from country to country. This thesis examines the current wind load provisions of the American Society of Civil Engineers Standard (ASCE 7, 2022), the National Building Code of Canada (NBCC, 2020), the European Standard (EN 1991-1-4, 2005), the Australian/New Zealand Standard (AS/NZS 1170.2, 2021), and the National Standard of the People’s Republic of China (GB 50009, 2012) in terms of exposure, and results are compared and discussed. First, the wind load provisions of ASCE 7 (2022) are considered to illustrate the process that most of the provisions follow. For homogeneous exposure, the terrain roughness categories and the corresponding exposure factors are compared. Additionally, the suggested minimum upstream fetch length for different exposure types is discussed by comparing them with the latest research findings. For non-homogeneous exposure, equations to calculate small-scale roughness change in various provisions are assessed by comparing them with wind tunnel experimental data. The inconsistencies between different provisions are identified, and remedies are proposed to minimize or avoid various errors, which are sometimes subjective. Other approaches such as the internal boundary layer (IBL) theory-based method, the morphometric method, the anemometric method, and the geographic information system (GIS)-based method are reviewed. It was found that it is usually expensive or time-consuming to estimate the exposure coefficients through these methods, particularly in complex terrain. Therefore, an innovative approach to estimate the value of zo based on Google Earth Pro is proposed, and this approach is efficient and freely available. Two case studies, namely, London, UK and the Tampa International Airport, Florida, were adopted to verify the accuracy of the proposed method and yielded satisfactory results. This thesis also investigates the effects of upstream exposure on environmental wind engineering problems by taking pedestrian-level wind (PLW) velocity cases as typical examples. The methodology of computational wind engineering (CWE), which works better on environmental challenges than on structural wind engineering problems, is adopted, and the expected discrepancies in the results for typical cases are established and assessed. The sensitivity of the PLW velocity factors to the upstream exposure fetch is documented and discussed. The research presented in the thesis demonstrates a great potential to contribute to further development of wind standards and codes of practice, as far as the characterization of the upstream exposure is concerned, at the national and international level (ISO)