Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences最新文献

City-scale buoyancy-driven flow is paramount for the dispersion of city pollutants and heat removal under calm and stable atmospheric conditions. Previous studies have assumed reduced-scale models can represent the characteristics of full-scale urban heat dome flows when the non-dimensional Froude number (Fr) is of similar magnitude after entering the Reynolds number (Re) independence regime. However, critical Re values were not well quantified for urban heat dome flows, especially in reduced-scale models. In this study, the influences of Fr, Re and a newly defined dimensionless number (m_Fr) on urban heat dome flows over an idealized square city were studied. A specific Re value (Re = 2.98 × 10⁵) is associated with a critical Fr value of 0.003, while a given Fr value (Fr = 0.013) corresponds to a critical Re value of 1.6 × 10³ in reduced-scale models. Noticeable diagonal inflow at lower levels and side outflow at upper levels forms when Fr [Formula: see text] 0.003 and Re [Formula: see text] 1.6 × 10³. When the newly defined m_Fr is used, side outflow angles and flow structures of urban heat dome flows for both full-scale and reduced-scale models agree well with each other. This indicates that m_Fr can be regarded as a suitable dimensionless number for the similarity criterion in urban heat dome flow studies.This article is part of the theme issue 'Urban heat spreading above and below ground'.

The urban heat island (UHI) phenomenon presents pressing challenges for urban sustainability, intersecting urban planning, building design, public health and climate adaptation and mitigation policy. While UHI science has advanced, its knowledge and practice translation into real-life practice remains limited. This paper investigates the processes of how UHI knowledge can support the transition from diagnosing urban climate risks to shaping more thermally resilient cities. It begins by outlining the interdisciplinary significance of urban heat governance and highlights the persistent gap between scientific understanding and actionable outcomes by drawing from five global contexts-Japan, Germany, the United States, Hong Kong and Singapore. The paper explores how scientific insights are integrated into planning instruments, design regulations and environmental performance frameworks. Using an implementation science perspective, the paper examines four key themes: (i) barriers and enablers of science-policy integration, (ii) knowledge co-production, (iii) boundary objects and interfaces, and (iv) policy diffusion across cities. Findings emphasize the importance of institutional coordination, iterative co-production and simple and user-friendly tools for planners. The paper concludes by proposing a forward-looking research agenda focused on integrated modelling, climate-resilient design and community-driven approaches, contributing to a growing discourse on reorienting urban climatology towards practice for more equitable and sustainable cities.This article is part of the theme issue 'Urban heat spreading above and below ground'.

Urban heat is a growing concern especially under global climate change and continuous urbanization. However, the understanding of its spatiotemporal propagation behaviours remains limited. In this study, we leverage a data-driven modelling framework that integrates causal inference, network topology analysis and dynamic synchronization to investigate the structure and evolution of temperature-based causal networks across the continental United States. We perform the first systematic comparison of causal networks constructed using warm-season daytime and nighttime air temperature anomalies in urban and surrounding rural areas. Results suggest strong spatial coherence of network links, especially during nighttime, and small-world properties across all cases. In addition, urban heat dynamics becomes increasingly synchronized across cities over time, particularly for maximum air temperature. Different network centrality measures consistently identify the Great Lakes region as a key mediator for spreading and mediating heat perturbations. This system-level analysis provides new insights into the spatial organization and dynamic behaviours of urban heat in a changing climate.This article is part of the theme issue 'Urban heat spreading above and below ground'.

The subsurface of cities is warming up-undergoing an underground climate change caused by subsurface urban heat islands (SUHIs). This phenomenon poses hazards while offering opportunities for sustainable urban heating. Although the morphology of urban areas above the ground is renowned for markedly influencing surface heat islands, the impact of the underground urban morphology on SUHIs remains largely unexplored. This study aims to (i) extend the definition of quantitative variables for analysing the urban morphology from the surface to the subsurface of cities and (ii) systematically examine how the underground urban morphology affects the intensity of SUHIs. Using three-dimensional (3D), time-dependent finite element simulations, we assess the role of different underground morphological features of cities in the development and intensity of SUHIs, such as heat source dimensions and distribution, green-space density and ground properties. Results indicate that the size and density of underground heat sources primarily drive the overall intensity of SUHIs, strongly depending on the presence of groundwater flow and only secondarily on the ground thermo-physical properties and the presence of green areas at the surface, whose influence substantially vary with depth. These findings enhance the understanding of the mechanisms governing SUHIs and provide insights to mitigate them globally.This article is part of the theme issue 'Urban heat spreading above and below ground'.

Managing urban groundwater resources is crucial not only for water quantity questions, but also to safeguard water quality. While evaluating hydrochemical parameters is part of common monitoring strategies, given the ongoing trend of geothermal energy usage, the evaluation of thermal regimes has gained increasing interest. This study presents an analysis of groundwater temperature (GWT) datasets from conventional monitoring networks and from seven high-resolution multi-level monitoring systems in Basel City, Switzerland. With GWT hotspots of up to 20°C, the monitoring data clearly showed the transient development of a subsurface urban heat island (SUHI). An existing suite of three-dimensional thermal hydraulic (3D-TH) models for four distinct groundwater bodies (GWB) was updated to enable SUHI analysis. For this, GWT, groundwater heads, river temperatures, river stages and groundwater user data were merged and introduced into the 3D-TH, enabling a 6-year calibration plus a 5-year validation period. The updated models provide insights into the long-term groundwater and heat flux dynamics across Basel's GWB. The findings underscore the flexibility of monitoring and modelling in evaluating urban groundwater systems, promoting a sustainable use and management of shallow geothermal energy and formulating SUHI mitigation strategies.This article is part of the theme issue 'Urban heat spreading above and below ground'.

Predicting city-scale air flows such as urban heat island circulations (UHIC) is challenging following the interaction of microscale winds (buildings, neighbourhoods and districts), and mesoscale winds beyond a city. Being at an intermediate scale, UHIC has been studied using both microscale prediction tools, e.g. computational fluid dynamics (CFD) and mesoscale weather forecasting tools, e.g. weather research and forecasting (WRF). A thorough comparison of the UHIC simulation capacities of these two classes of models has not been performed so far. In addition, current mesoscale models generally cannot resolve building-specific details or simulate fine-scale turbulence structures. Consequently, microscale models, such as the Parallelized Large-Eddy Simulation Model (PALM) and ANSYS Fluent, have gained prominence, as they can simulate building-resolved features. This study evaluates the trade-offs associated with the above-mentioned mesoscale and microscale models for a UHIC above an idealized square city with known complex flow patterns. The results show that WRF is computationally efficient and has a computational cost approximately one order of magnitude less than that of microscale models. However, WRF exhibits lower accuracy, particularly in capturing localized effects at a ground level. Fluent and PALM offer higher accuracy by simulating finer details at a higher computational cost than WRF. PALM and Fluent also exhibit similar accuracy, and PALM is more computationally efficient than Fluent. However, unlike Fluent, the use of Cartesian grids with PALM limits its ability in handling complex building shapes. Our results are useful for selecting the suitable city-scale prediction tools considering both computational costs and accuracy.This article is part of the theme issue 'Urban heat spreading above and below ground'.

In this study, we investigate the geothermal potential of the shallow subsurface in Dresden, Germany. The analysis considers the status quo scenario in which accumulated heat can be recycled. Installing all possible geothermal systems based on the available space, this heat could supply Dresden's residents for 3 years with energy for space heating. However, a fair CO₂ price would have to be implemented to improve economic value. Next, a near-future scenario is studied, in which accumulated heat has been recycled and, considering all technical constraints, the annual heat input provides a sustainable potential that can provide up to 4.5% of annual heating demands (HDs). However, there is a very high spatial variability that is studied in regard to its socio-economic implications. Finally, two far-future scenarios (SSP245 and SSP585) are studied to understand the effect of climate change on the suitability of geothermal systems. Depending on the scenario and circumstances, up to 82% of the city's climate neutrality targets might be reached.This article is part of the theme issue 'Urban heat spreading above and below ground'.

Heat islands have been recognied at the surface of urban areas since the nineteenth century, while their subsurface counterparts were only identified in the late twentieth century. Since then, surface and subsurface urban heat islands (UHIs and SUHIs), respectively have drawn increasing scientific attention, along with technologies and policies designed to limit their impacts on public comfort and health, infrastructure resilience, the environment and energy efficiency. Yet they have been traditionally studied in isolation. This Theme Issue seeks to bridge that gap by presenting recent advances on Urban Heat Above and Below Ground. As the introductory piece of this compilation of works, this article provides an overview of the drivers and impacts of UHIs and SUHIs and offers a perspective on the need to transition towards integrated studies that explicitly account for the thermal interactions between the urban surface and subsurface. Three priority research directions are outlined to address overlooked aspects of urban heat propagation and improve the fidelity of analyses, with a focus on computational simulations. The article concludes by summarizing the contributions in this Theme Issue, which expand knowledge of urban heat dynamics and lay the foundation for capturing the full three-dimensional thermal complexity of cities-above and below ground.This article is part of the theme issue 'Urban heat spreading above and below ground'.

Europe is consistently experiencing hottest summers. Understanding people's thermal comfort and stress and responses to heatwaves has become increasingly important. While much of the literature has recognized the overheating risks in the UK's domestic housing stock, there remain short comings in analysing residents' indoor heat exposure during heatwaves. This research aims to investigate the mini heatwaves occurring in domestic environments and to explore the factors influencing residents' responses to heatwaves. A sensor-enhanced housing data survey was conducted in Southwark, London, over two summer months of 2023 during heatwave events. This study integrates outdoor weather data, sensor-measured high temporal-resolution indoor environmental conditions, the Index for Multiple Deprivation (IMD) and building features to analyse indoor heatwaves and thermal comfort. The article breaks ground by advancing existing discussions of urban heat stress, which typically focus on outdoor environments, by specifically examining indoor heat exposure intensities and the associated risks owing to vulnerability from asymmetry in adaptive capacities. In addition, the article aims to complement the current heatwave classifications based on the domestic heatwaves experienced by residents.This article is part of the theme issue 'Urban heat spreading above and below ground'.

The article investigates the interaction between the sea-breeze circulation and the urban heat island effect in Houston, Texas, located on the Gulf of Mexico coast. The analysis focuses on the summer period in 2022 during the Convective-cloud Urban Boundary-layer Experiment and the Tracking Aerosol Cloud Convection Interactions Experiment. The work, which exclusively used ground-based observations, found a high degree of intra-urban variability in both the temperature and the humidity field during the sea-breeze days. Near-surface virtual potential temperature during the sea-breeze episodes in the metropolitan area varied by almost 10 K, with urban regions near the coast experiencing lower temperature than the inland region. The urban heat island effect was strong enough to create persistent hot spots even during the sea-breeze episodes. On land-breeze days, both the temperature and the humidity fields were more uniform with little spatial variability. The depth of the sea-breeze circulation was captured using X-band radar and radiosondes; it averaged around 1500-2000 m above ground level. The thermal gradient due to the interaction between the sea-breeze circulation and the urban heat island effect led to secondary flows that influenced local convective activity.This article is part of the theme issue 'Urban heat spreading above and below ground'.