Climate and More Sustainable Cities: Climate Information for Improved Planning and Management of Cities (Producers/Capabilities Perspective)

Edge AI and Blockchain for Smart Sustainable Cities: Promise and Potential

Modern cities worldwide are undergoing radical changes to foster a clean, sustainable and secure environment, install smart infrastructures, deliver intelligent services to residents, and facilitate access for vulnerable groups. The adoption of new technologies is at the heart of implementing many initiatives to address critical concerns in urban mobility, healthcare, water management, clean energy production and consumption, energy saving, housing, safety, and accessibility. Given the advancements in sensing and communication technologies over the past few decades, exploring the adoption of recent and innovative technologies is critical to addressing these concerns and making cities more innovative, sustainable, and safer. This article provides a broad understanding of the current urban challenges faced by smart cities. It highlights two new technological advances, edge artificial intelligence (edge AI) and Blockchain, and analyzes their transformative potential to make our cities smarter. In addition, it explores the multiple uses of edge AI and Blockchain technologies in the fields of smart mobility and smart energy and reviews relevant research efforts in these two critical areas of modern smart cities. It highlights the various algorithms to handle vehicle detection, counting, speed identification to address the problem of traffic congestion and the different use-cases of Blockchain in terms of trustworthy communications and trading between vehicles and smart energy trading. This review paper is expected to serve as a guideline for future research on adopting edge AI and Blockchain in other smart city domains.

Numerical Investigations of Urban Pollutant Dispersion and Building Intake Fraction with Various 3D Building Configurations and Tree Plantings

Rapid urbanisation and rising vehicular emissions aggravate urban air pollution. Outdoor pollutants could diffuse indoors through infiltration or ventilation, leading to residents’ exposure. This study performed CFD simulations with a standard k-ε model to investigate the impacts of building configurations and tree planting on airflows, pollutant (CO) dispersion, and personal exposure in 3D urban micro-environments (aspect ratio = H/W = 30 m, building packing density λp = λf = 0.25) under neutral atmospheric conditions. The numerical models are well validated by wind tunnel data. The impacts of open space, central high-rise building and tree planting (leaf area density LAD= 1 m2/m3) with four approaching wind directions (parallel 0° and non-parallel 15°, 30°, 45°) are explored. Building intake fraction <P_IF> is adopted for exposure assessment. The change rates of <P_IF> demonstrate the impacts of different urban layouts on the traffic exhaust exposure on residents. The results show that open space increases the spatially-averaged velocity ratio (VR) for the whole area by 0.40−2.27%. Central high-rise building (2H) can increase wind speed by 4.73−23.36% and decrease the CO concentration by 4.39−23.00%. Central open space and high-rise building decrease <P_IF> under all four wind directions, by 6.56−16.08% and 9.59−24.70%, respectively. Tree planting reduces wind speed in all cases, raising <P_IF> by 14.89−50.19%. This work could provide helpful scientific references for public health and sustainable urban planning.

Poor Air Quality in Urban Settings: A Comparison of Perceptual Indicators, Causes and Management in Two Cities

Poor air quality (PAQ) is a global concern, especially in urban areas, and is often seen as an important element of social sustainability given its negative impact on health and quality of life. However, little research has been undertaken in cities of the developing world to explore how residents perceive poor air quality, its main causes, what control measures should be used to address PAQ and where the main responsibility rests for implementing control measures. The research described in this paper sought to address these points, using a questionnaire-based survey (n = 262) in Nigeria’s federal capital city of Abuja (n = 137) and the state-capital city of Enugu (n = 125). The survey took place during the COVID-19 pandemic (October 2020 to March 2021), and was stratified to ensure representation across a number of demographic groups such as gender, age, education and income. The results were analysed using the Kruskal–Wallis non-parametric test and Hochberg’s post hoc test available in SPSS version 28. The study found that the ranking of perceptual indicators and the main causes of PAQ had much agreement between respondents from both cities and between demographic groups. Smoke, odour and dust particles were perceived to be the most important indicators of PAQ, while the main sources of PAQ were waste and bush burning, vehicle use and power generators. The two most preferred control measures were proper waste management and the avoidance of bush burning. However, there was a significant difference between the two cities in terms of the main organisations responsible for addressing PAQ, with respondents from Abuja citing the federal government, while those from Enugu cited the state government. Interestingly, younger people in Enugu noted that the government should take more responsibility in controlling PAQ than did the older demographic in that city, but this difference was not seen in Abuja. Overall, this study reveals that residents in these two Nigerian cities clearly recognise their exposure to PAQ and it suggests that these perceptual indicators, and views on sources and interventions should be central to designing policies to control this important issue.

Impact of Indoor-Outdoor Temperature Difference on Building Ventilation and Pollutant Dispersion within Urban Communities

Mechanical ventilation consumes a huge amount of global energy. Natural ventilation is a crucial solution for reducing energy consumption and enhancing the capacity of atmospheric self-purification. This paper evaluates the impacts of indoor-outdoor temperature differences on building ventilation and indoor-outdoor air pollutant dispersion in urban areas. The Computational Fluid Dynamics (CFD) method is employed to simulate the flow fields in the street canyon and indoor environment. Ventilation conditions of single-side ventilation mode and cross-ventilation mode are investigated. Air change rate, normalized concentration of traffic-related air pollutant (CO), intake fraction and exposure concentration are calculated to for ventilation efficiency investigation and exposure assessment. The results show that cross ventilation increases the air change rate for residential buildings under isothermal conditions. With the indoor-outdoor temperature difference, heating could increase the air change rate of the single-side ventilation mode but restrain the capability of the cross-ventilation mode in part of the floors. Heavier polluted areas appear in the upstream areas of single-side ventilation modes, and the pollutant can diffuse to middle-upper floors in cross-ventilation modes. Cross ventilation mitigates the environmental health stress for the indoor environment when indoor-outdoor temperature difference exits and the personal intake fraction is decreased by about 66% compared to the single-side ventilation. Moreover, the existence of indoor-outdoor temperature differences can clearly decrease the risk of indoor personal exposure under both two natural ventilation modes. The study numerically investigates the building ventilation and pollutant dispersion in the urban community with natural ventilation. The method and the results are helpful references for optimizing the building ventilation plan and improving indoor air quality.

Measurements and simulations of energy fluxes over a high-rise and compact urban area in Hong Kong

Measuring energy fluxes in a dense and high-rise urban area is extremely challenging, thus our knowledge in such area remains limited. This study assessed the surface energy fluxes and investigated the energy balance closure (EBC) over such complex urban surface in Hong Kong. Net radiation (Q_N), sensible (Q_H) and latent (Q_E) heat fluxes were measured using an eddy covariance system from September 2018 to August 2019. Anthropogenic heat flux (Q_F) was simulated by a large-scale urban energy model (i.e., LUCY) and validated by an anthropogenic heat database (i.e., AHE_KL). Storage heat flux (Q_S) was estimated by an objective hysteresis model (OHM). Among five energy terms, Q_F showed the largest values of around 750 Wm^-2 especially in the afternoon. Whereas, Q_E varying within 150 Wm^-2 showed the smallest values. The variation range of net radiation, sensible heat flux and storage heat was respectively from -50 to 600, 0 to 450 and -30 to 300 W m^-2. EBC generally showed a negative relationship with surface heterogeneity. Best EBC was observed in the direction with a relatively constant and large aspect ratio, and with the most occurrence of unstable stratifications. The uncertainties of Q_H and Q_E fluxes were respectively estimated to be approximately 8% and 7%. The result of LUCY was consistent with that of AHE_KL. EBC was not sensitive to different coefficients estimating Q_S. This study helped to fill a gap in our understanding of surface energy and turbulent fluxes in compact cities with high-rise buildings and shed insights into the future installation of eddy covariance tower in similar areas. The required height of the eddy covariance tower in such urban sites might not be as restrictive as that in other urban areas with low-rise buildings or with low building density, thus making it more feasible to set up such observation towers.

Integrated impacts of tree planting and aspect ratios on thermal environment in street canyons by scaled outdoor experiments

Urban tree planting has the potential to reduce urban heat island intensity and building energy consumption. However, the heterogeneity of cities makes it difficult to quantitatively assess the integrated impacts of tree planting and street layouts. Scaled outdoor experiments were conducted to investigate the influence of tree plantings on wind and thermal environments in two-dimensional (2D) north-south oriented street canyons with various aspect ratios (building height/street width, AR = H/W = 1, 2, 3; H = 1.2 m). The effects of tree species with similar leaf area index (C. kotoense, big crown; C. macrocarpa, small crown), tree planting densities (ρ = 1, 0.5), and arrangements (double-row, single-row) were considered. Vegetation reduces pedestrian-level wind speed by 29%-70%. For ρ = 1 and single-row arrangement, C. kotoense (big crown) has a better shading effect and decreases wall and air temperature during the daytime by up to 9.4 °C and 1.2 °C, respectively. In contrast, C. macrocarpa (small crown) leads to a temperature increase at the pedestrian level. Moreover, C. kotoense raises the air and wall temperature of the upper urban canopy layer and increases the street albedo during the daytime because of the solar radiation reflected by trees. C. kotoense/C. macrocarpa produces the maximum daytime cooling/warming and nighttime warming of air temperature when H/W = 2 owing to its weaker convective heat transfer. When H/W = 3, the building shade dominates the shading cooling and tree cooling is less significant. When ρ = 1, double-row trees (C. kotoense) reduce wall and air temperatures by up to 10.0 °C and 1.0 °C during the daytime. However, reducing ρ from 1 to 0.5 weakens the capacity of daytime cooling by C. kotoense and the warming effect by C. macrocarpa. Our study quantifies the influence of tree planting and aspect ratios on the thermal environment, which can provide meaningful references for urban tree planting and produce high-quality validation data for numerical modeling.

Temperature Response from the Change of Surface Heat Flux and Vertical Diffusivity by Urbanization

A 1-D diffusion model of temperature is employed to understand important features of temperature response to the changes of surface heat flux (SHF) and vertical diffusivity shown in 3-D model simulations. Analytical results show that the temperature response to the SHF change is the convolution of the SHF change and Green’s function (GF). Because the GF is inversely proportional to the square root of diffusion coefficient near the surface, weak/strong diffusivity in the early morning/noontime tends to generate a large/small temperature response by slowing/accelerating heat flow from surface to the atmosphere. The modulation effect of the GF and the convolution effect explain very different temperature responses to the SHF change during each period. Analytical results also show that the temperature response to the change of DF is equal to the convolution of the product of diffusion coefficient change, vertical gradients of reference temperature and the GF. Because the vertical gradient of the GF is negative below 80 m, enhanced/reduced diffusivity would enhance/weaken the urban temperature, if the vertical gradient of reference temperature is negative/positive. Numerical results with typical values of the changes of SHF and diffusivity suggest that the changes of SHF has the dominant contribution to the temperature response.

Integrated urban hydrometeorological, climate and environmental services: Concept, methodology and key messages

Integrated Urban hydrometeorological, climate and environmental Services (IUS) is a World Meteorological Organization (WMO) initiative to aid development of science-based services to support safe, healthy, resilient and climate friendly cities. Guidance for Integrated Urban Hydrometeorological, Climate and Environmental Services (Volume I) has been developed with the intent to provide an overview of the concept, methods and good practices for producing and providing these services to respond to urban hazards across a range of time scales (weather to climate). This involves combining (dense) heterogeneous observation networks, high-resolution forecasts, multi-hazard early warning systems and climate services to assist cities in setting and implementing mitigation and adaptation strategies for the management and building of resilient and sustainable cities. IUS includes research, evaluation and delivery with a wide participation from city governments, national hydrometeorological services, international organizations, universities, research institutions and private sector stakeholders. An overview of the IUS concept with key messages, examples of good practice and recommendations are provided. The research community will play an important role to: identify critical research challenges; develop impact forecasts and warnings; promote and deliver IUS internationally, and; support national and local communities in the implementation of IUS thereby contributing to the United Nations' Sustainable Development Goals at all scales.

A review of the impact of blue space on the urban microclimate

The urban heat island (UHI) phenomenon represents a major public health issue and has received great attention due to rapid urbanisation. Blue spaces have long been considered a possible mitigation strategy to ameliorate the UHI. However, our knowledge regarding the interaction of waterbodies with their urban surroundings is still limited. This review attempts through a comparative analysis of the available literature to examine the thermal effects of static blue spaces on the urban climate. Remote sensing studies are the most common approach analysed in this review but there is a clear disparity between the cooling potentials reported by remote sensing as opposed to field measurements or numerical simulations, likely due to a lack of nocturnal measurements, when warming due to thermal inertia can occur and consideration of the latent heat flux. The size and shape of blue spaces are shown to be important variables for the cooling achieved in urban settings but there is no consensus in the literature. This is likely due to the different locations and climates of the studies, it can be hypothesised that in locations with an even distribution of wind directions a rounder waterbody is more effective while in locations where wind direction is more uniform an elongated waterbody aligned to the wind is more effective due to the increased fetch. From the analysis of the literature, it is clear that there is still a distinct knowledge gap regarding the physical interpretation of waterbodies' contribution to the urban climate. There is also a current lack of information about the diurnal and seasonal variability of the various structures and processes. There is evidence, however, that the comfort achieved by sensible cooling can be offset by the increased water vapour content and that during the night blue spaces may actually exacerbate the UHI, reducing urban thermal comfort.

Scaled outdoor experimental studies of urban thermal environment in street canyon models with various aspect ratios and thermal storage

Street aspect ratios and urban thermal storage largely determine the thermal environment in cities. By performing scaled outdoor measurements in summer of 2017 in Guangzhou, China, we investigate these impacts on spatial/temporal characteristics of urban thermal environment which are still unclear so far. Two types of street canyon models are investigated, i.e. the 'hollow' model resembling hollow concrete buildings and the 'sand' model consisting of buildings filled with sand attaining much greater thermal storage. For each model, three street aspect ratios (building height/street width, H/W = 1, 2, 3; H = 1.2 m) are considered. The diurnal variations of air-wall surface temperatures are observed and their characteristics are quantified for various cases. The daily average temperature and daily temperature range (DTR) of wall temperature vary significantly with different aspect ratios and thermal storage. During the daytime, wider street canyon (H/W = 1) with less shading area experiences higher temperature than narrower ones (H/W = 2, 3) as more solar radiation received by wall surfaces. At night, wider street canyon cools down quicker due to stronger upward longwave radiation and night ventilation. For hollow models, H/W = 1 attains DTR of 12.1 °C, which is 1.2 and 2.1 °C larger than that of H/W = 2, 3. Moreover, the sand models experience smaller DTR and a less changing rate of wall temperature than hollow models because larger thermal storage absorbs more heat in the daytime and releases more at night. DTR of hollow models with H/W = 1, 2, 3 is 4.5, 4.6 and 3.8 °C greater than sand models respectively. For both hollow and sand models, wider streets experience a little higher daily average temperature (0.3-0.6 °C) than narrower ones. Our study provides direct evidence in how man-made urban structures influence urban climate and also suggests the possibility to control outdoor thermal environment by optimize urban morphology and thermal storage.

Convivial Greenstreets: A Concept for Climate-Responsive Urban Design

This paper presents a conceptual framework for using “convivial greenstreets” (CG) as a resource for climate adaptation. When applied consistently, CG can become an emerging green practice with a positive impact on urban adaptation to climate change: CG may provide localized climate amelioration in ways that support social engagement outdoors. However, as spontaneous phenomena, CG should neither become an academic nor an aesthetic prescriptive tool. How then can CG be used as an active resource for urban adaptation to climate change while avoiding these two potential pitfalls? To explore this question, we present the concept of CG and the ways it can be situated in theoretical urbanism and analogous urban morphologies. We profile the CG inventory corpus and conceptualization that has taken place to date and expand them through a climate-responsive urban design lens. We then discuss how CG and climate-responsive urban design can be brought together while preventing the academization and aestheticizing of the former. This discussion is illustrated with a group of visualizations. We conclude by submitting that climate-responsive urban design and extensive and robust CG practices can co-operate to promote more resilient communities and urban climates. Finally, the conceptual framework herein sets an agenda for future research.

Urban-rural moisture contrast: Regulator of the urban heat island and heatwaves' synergy over a mediterranean city

The current study observed the effect of the synergistic interaction of urban heat island (UHI) and heatwaves (HWs) which is different from the sum of their separate effects on the medium-sized town of Nicosia, Cyprus. From an analysis of hourly meteorological records of eight consecutive years (2007-2014) we defined HWs with respect to air temperature (T95-over the 95th percentile air temperatures) as well as the heat index (HI65-heat index over 65degC) and studied their effects on the local UHI phenomenon. Both heatwave types were characterized by increased air temperature, lower wind speed and increased absolute humidity. HWs defined using the heat index (HI65) occurred more frequently and persisted for a longer period of time. UHI was intensified to about 0.9-1.3 °C during daytime hours under both HW definitions which was attributed to the evaporation of dew deposited on the upper top layer of soil that suppressed higher temperatures in the rural station due to a prolonged cooling effect. Model estimates of dew formation overnight and evaporation in the morning hours are hypothesized to be the main contributing factor in keeping rural air temperatures lower, thus increasing the UHI intensity. The results emphasize the critical role of latent cooling and evapotranspiration as a mitigation factor affecting extreme local temperatures.

Is Sensible Heat Flux Useful for the Assessment of Thermal Vulnerability in Seoul (Korea)?

Climate change has led to increases in global temperatures, raising concerns regarding the threat of lethal heat waves and deterioration of the thermal environment. In the present study, we adopted two methods for spatial modelling of the thermal environment based on sensible heat and temperature. A vulnerability map reflecting daytime temperature was derived to plot thermal vulnerability based on sensible heat and climate change exposure factors. The correlation (0.73) between spatial distribution of sensible heat vulnerability and mortality rate was significantly greater than that (0.30) between the spatial distribution of temperature vulnerability and mortality rate. These findings indicate that deriving thermally vulnerable areas based on sensible heat are more objective than thermally vulnerable areas based on existing temperatures. Our findings support the notion that the distribution of sensible heat vulnerability at the community level is useful for evaluating the thermal environment in specific neighbourhoods. Thus, our results may aid in establishing spatial planning standards to improve environmental sustainability in a metropolitan community.

Urban Areas and Urban–Rural Contrasts under Climate Change: What Does the EURO-CORDEX Ensemble Tell Us?—Investigating near Surface Humidity in Berlin and Its Surroundings

Climate change will impact urban areas. Decision makers need useful climate information to adapt adequately. This research aims to improve understanding of changes in moisture and temperature projected under climate change in Berlin compared to its surroundings. Simulations for the Representative Concentration Pathway (RCP) 8.5 scenario from the European Coordinated Regional Climate Downscaling Experiment (EURO-CORDEX) 0.11° are analyzed, showing a difference in moisture and temperature variables between Berlin and its surroundings. The running mean over 30 years shows a divergence throughout the twenty-first century for relative humidity between Berlin and its surroundings. Under this scenario, Berlin gets drier over time. The Mann-Kendall test quantifies a robust decreasing trend in relative humidity for the multi-model ensemble throughout the twenty-first century. The Mann-Whitney-Wilcoxon test for relative humidity indicates a robust climate change signal in Berlin. It is drier and warmer in Berlin compared to its surroundings for all months with the largest difference existing in summer. Additionally, the change in humidity for the period 2070–2099 compared to 1971–2000 is larger in the summer months. This study presents results to better understand near surface moisture change and related variables under long-term climate change in urban areas compared to their rural surroundings using a regional climate multi-model ensemble.

Determining Favourable and Unfavourable Thermal Areas in Seoul Using In-Situ Measurements: A Preliminary Step towards Developing a Smart City

Urban heat island effects (UHIE) are becoming increasingly widespread, thus, there is an urgent need to address thermal comfort, which significantly influences the daily lives of people. In this study, a means of improving the thermal environment by spatial analysis of heat was implemented to ensure basic thermal comfort in future smart cities. Using Seoul as the study site, the relationship between sensible heat and land cover type was used to identify heat islands in this city. Thereafter, k-means clustering was employed to extract unfavourable and favourable thermal areas. High sensible heat indicates locations where environmental heat needs to be mitigated. Sensible heat distribution data were used for spatial typification to formulate an effective land cover factor to mitigate the UHIE. In-situ net radiation data measured at six sites were utilised to confirm the spatial typification of the thermal environment. It was found that expanding the green space by 1% reduces the sensible heat by 4.9 W/m2. Further, the building coverage ratio and green coverage influence the sensible heat in compact residential areas. The study results can be used to establish spatial planning standards to improve the thermal environments of sustainable cities.

Urban energy exchanges monitoring from space

One important challenge facing the urbanization and global environmental change community is to understand the relation between urban form, energy use and carbon emissions. Missing from the current literature are scientific assessments that evaluate the impacts of different urban spatial units on energy fluxes; yet, this type of analysis is needed by urban planners, who recognize that local scale zoning affects energy consumption and local climate. Satellite-based estimation of urban energy fluxes at neighbourhood scale is still a challenge. Here we show the potential of the current satellite missions to retrieve urban energy budget fluxes, supported by meteorological observations and evaluated by direct flux measurements. We found an agreement within 5% between satellite and in-situ derived net all-wave radiation; and identified that wall facet fraction and urban materials type are the most important parameters for estimating heat storage of the urban canopy. The satellite approaches were found to underestimate measured turbulent heat fluxes, with sensible heat flux being most sensitive to surface temperature variation (-64.1, +69.3 W m-2 for ±2 K perturbation).  They also underestimate anthropogenic heat fluxes. However, reasonable spatial patterns are obtained for the latter allowing hot-spots to be identified, therefore supporting both urban planning and urban climate modelling.

China's adaptation to climate & urban climatic changes: A critical review

Since the conclusion of the 2014 Climate Summit in New York and the 21st Conference of the Parties (COP21) in Paris, China has been actively advancing its national policies on climate change mitigation and adaptation since more unpredictable extreme weather events are expected, which may incur a heavy cost in terms of economics and public health. Since China is still in the process of urbanisation, the greatest challenge it faces is finding a balance between economic growth and keeping carbon dioxide and greenhouse gas emission rates at a manageable level. Cities in China play a key role in the implementation of the central policies and make concrete actions in response to climate change. With reference to a series of recent policy papers and action plans as the background, this paper attempts to provide a critical overview of China's climate change action plans from the national to the city and urban level. It seeks to understand whether the proposed responses to climate change and strategies for actions on greening and air corridors for cities and urban areas are appropriate. It is found that for China to advance its urban climatic adaptation strategy there is a need for (1) urban data, (2) a cross-disciplinary impact assessment, and (3) the development of a market and policy transformation mechanism.

The influence of surface type on the absorbed radiation by a human under hot, dry conditions

Given the predominant use of heat-retaining materials in urban areas, numerous studies have addressed the urban heat island mitigation potential of various "cool" options, such as vegetation and high-albedo surfaces. The influence of altered radiational properties of such surfaces affects not only the air temperature within a microclimate, but more importantly the interactions of long- and short-wave radiation fluxes with the human body. Minimal studies have assessed how cool surfaces affect thermal comfort via changes in absorbed radiation by a human (R _abs) using real-world, rather than modeled, urban field data. The purpose of the current study is to assess the changes in the absorbed radiation by a human-a critical component of human energy budget models-based on surface type on hot summer days (air temperatures > 38.5^∘C). Field tests were conducted using a high-end microclimate station under predominantly clear sky conditions over ten surfaces with higher sky view factors in Lubbock, Texas. Three methods were used to measure and estimate R _abs: a cylindrical radiation thermometer (CRT), a net radiometer, and a theoretical estimation model. Results over dry surfaces suggest that the use of high-albedo surfaces to reduce overall urban heat gain may not improve acute human thermal comfort in clear conditions due to increased reflected radiation. Further, the use of low-cost instrumentation, such as the CRT, shows potential in quantifying radiative heat loads within urban areas at temporal scales of 5-10 min or greater, yet further research is needed. Fine-scale radiative information in urban areas can aid in the decision-making process for urban heat mitigation using non-vegetated urban surfaces, with surface type choice is dependent on the need for short-term thermal comfort, or reducing cumulative heat gain to the urban fabric.

MODIS Summer SUHI Cross-sections Anomalies over the Megacities of the Monsoon Asia Region and Global Trends

Background:

Evidence has accumulated in recent years regarding the scope of local and global climate changes attributed to exacerbating anthropogenic factors such as accelerating population growth, urbanization, industrialization, traffic and energy use. Remote space monitoring, unlike ground-based measurements, has the advantage of providing global coverage on a daily basis.

Methods:

MODIS (Moderate Resolution Imaging Spectroradiometer) Aqua and Terra 1°×1° spatial resolution as well as the 1 km higher resolution of Aqua-MODIS were investigated for a global overview of megacities temperature variations, as well as the recent trends of the 10 largest Monsoon Asian megacities.

Results:

The average Land Surface Temperature (LST) cross-sections of the 10 Asian megacities were examined for June-August 2002-2014. Temperature variations fit a spatial bell-shaped curve, with a pronounced maximum over the city center. Nighttime data indicated sharp LST decreases with distance from the city center, particularly in the coldest cities, those of Tokyo, Seoul, Osaka and Beijing.

Conclusion:

Daytime latitudinal (E-W) and longitudinal (N-S) Surface Urban Heat Islands (SUHI) have steeper gradients than for nighttime data. During daytime, the SUHI gradients are largest in Tokyo, Seoul, Osaka and Beijing with values reaching 15oC followed by the cities of Shanghai and Guangzhou with ~11oC, and Karachi with ~5oC SUHI. Nighttime SUHIs were more moderate, 4-6oC in Tokyo, Seoul ~5oC, Osaka 5-7oC and Beijing ~7oC. Only in the three largest megacities,i.e., Tokyo, Guangzhou and Shanghai, did the nighttime LST trends decline.

Supporting sustainability initiatives through biometeorology education and training

The International Society of Biometeorology (ISB) has covered significant breadth and depth addressing fundamental and applied societal and environmental challenges in the last 60 years. Biometeorology is an interdisciplinary science connecting living organisms to their environment, but there is very little understanding of the existence and placement of this discipline within formal educational systems and institutions. It is thus difficult to project the ability of members of the biometeorological community-especially the biometeorologists of the future-to help solve global challenges. In this paper, we ask: At present, how we are training people to understand and think about biometeorology? We also ask: What are the current tools and opportunities in which biometeorologists might address future challenges? Finally, we connect these two questions by asking: What type of new training and skill development is needed to better educate "biometeorologists of the future" to more effectively address the future challenges? To answer these questions, we provide quantitative and qualitative evidence from an educationally focused workshop attended by new professionals in biometeorology. We identify four common themes (thermal comfort and exposures, agricultural productivity, air quality, and urbanization) that biometeorologists are currently studying and that we expect to be important in the future based on their alignment with the United Nations Sustainable Development Goals. Review of recent literature within each of these thematic areas highlights a wide array of skill sets and perspectives that biometeorologists are already using. Current and new professionals within the ISB have noted highly varying and largely improvised educational pathways into the field. While variability and improvisation may be assets in promoting flexibility, adaptation, and interdisciplinarity, the lack of formal training in biometeorology raises concerns about the extent to which continuing generations of scholars will identify and engage with the community of scholarship that the ISB has developed over its 60-year history.

Utilising green and bluespace to mitigate urban heat island intensity

It has long been recognised that cities exhibit their own microclimate and are typically warmer than the surrounding rural areas. This 'mesoscale' influence is known as the urban heat island (UHI) effect and results largely from modification of surface properties leading to greater absorption of solar radiation, reduced convective cooling and lower water evaporation rates. Cities typically contain less vegetation and bodies of water than rural areas, and existing green and bluespace is often under threat from increasing population densities. This paper presents a meta-analysis of the key ways in which green and bluespace affect both urban canopy- and boundary-layer temperatures, examined from the perspectives of city-planning, urban climatology and climate science. The analysis suggests that the evapotranspiration-based cooling influence of both green and bluespace is primarily relevant for urban canopy-layer conditions, and that tree-dominated greenspace offers the greatest heat stress relief when it is most needed. However, the magnitude and transport of cooling experienced depends on size, spread, and geometry of greenspaces, with some solitary large parks found to offer minimal boundary-layer cooling. Contribution to cooling at the scale of the urban boundary-layer climate is attributed mainly to greenspace increasing surface roughness and thereby improving convection efficiency rather than evaporation. Although bluespace cooling and transport during the day can be substantial, nocturnal warming is highlighted as likely when conditions are most oppressive. However, when both features are employed together they can offer many synergistic ecosystem benefits including cooling. The ways in which green and bluespace infrastructure is applied in future urban growth strategies, particularly in countries expected to experience rapid urbanisation, warrants greater consideration in urban planning policy to mitigate the adverse effects of the UHI and enhance climate resilience.

Attenuating the surface Urban Heat Island within the Local Thermal Zones through land surface modification

Inefficient mitigation of excessive heat is attributed to the discrepancy between the scope of climate research and conventional planning practice. This study approaches this problem at both domains. Generally, the study, on one hand, claims that the climate research of the temperature phenomenon should be at local scale, where implementation of planning and design strategies can be more feasible. On the other hand, the study suggests that the land surface factors should be organized into zones or patches, which conforms to the urban planning and design manner. Thus in each zone, the land surface composition of those excessively hot places can be compared to the zonal standard. The comparison gives guidance to the modification of the land surface factors at the target places. Specifically, this study concerns the Land Surface Temperature (LST) in Wuhan, China. The land surface is classified into Local Thermal Zones (LTZ). The specifications of temperature sensitive land surface factors are relative homogeneous in each zone and so is the variation of the LST. By extending the city scale analysis of Urban Heat Island into local scale, the Local Surface Urban Heat Islands (LSUHIs) are extracted. Those places in each zone that constantly maintain as LSUHI and exceed the homogenous LST variation are considered as target places or hotspots with higher mitigation or adaptation priority. The operation is equivalent to attenuate the abnormal LST variation in each zone. The framework is practical in the form of prioritization and zoning, and mitigation strategies are essentially operated locally.

Assessment of human thermal perception in the hot-humid climate of Dar es Salaam, Tanzania

Dar es Salaam, Tanzania, is a typical African city along the Indian Ocean coast, and therefore an important urban area to examine human thermal perception in the hot-humid tropical climate. Earlier research on human bioclimate at Dar es Salaam indicated that heat stress prevails during the hot season from October to March, peaking between December and February, particularly the early afternoons. In order to assess the human thermal perception and adaptation, two popular places, one at an urban park and another at a beach environment, were selected and questionnaire surveys were conducted in August-September 2013 and January 2014, concurrently with local micro-meteorological measurements at survey locations. The thermal conditions were quantified in terms of the thermal index of the physiologically equivalent temperature (PET) using the micro-scale climate model RayMan. The thermal comfort range of human thermal comfort and the local thermal adaptive capacity were determined in respect to the thermal index by binning thermal sensation votes. The thermal comfort range was found to be well above that in temperate climates at about 23-31 °C of PET. The study could significantly contribute to urban planning in Dar es Salaam and other coastal cities in the tropics.

The Birmingham Urban Climate Laboratory-A high density, urban meteorological dataset, from 2012-2014

There is a paucity of urban meteorological observations worldwide, hindering progress in understanding and mitigating urban meteorological hazards and extremes. High quality urban datasets are required to monitor the impacts of climatological events, whilst providing data for evaluation of numerical models. The Birmingham Urban Climate Laboratory was established as an exemplar network to meet this demand for urban canopy layer observations. It comprises of an array of 84 wireless air temperature sensors nested within a coarser array of 24 automatic weather stations, with observations available between June 2012 and December 2014. data routinely underwent quality control, follows the ISO 8601 naming format and benefits from extensive site metadata. The data have been used to investigate the structure of the urban heat island in Birmingham and its associated societal and infrastructural impacts. The network is now being repurposed into a testbed for the assessment of crowd-sourced and satellite data, but the original dataset is now available for further analysis, and an open invitation is extended for its academic use.

Heat and Humidity in the City: Neighborhood Heat Index Variability in a Mid-Sized City in the Southeastern United States

Daily weather conditions for an entire city are usually represented by a single weather station, often located at a nearby airport. This resolution of atmospheric data fails to recognize the microscale climatic variability associated with land use decisions across and within urban neighborhoods. This study uses heat index, a measure of the combined effects of temperature and humidity, to assess the variability of heat exposure from ten weather stations across four urban neighborhoods and two control locations (downtown and in a nearby nature center) in Knoxville, Tennessee, USA. Results suggest that trees may negate a portion of excess urban heat, but are also associated with greater humidity. As a result, the heat index of locations with more trees is significantly higher than downtown and areas with fewer trees. Trees may also reduce heat stress by shading individuals from incoming radiation, though this is not considered in this study. Greater amounts of impervious surfaces correspond with reduced evapotranspiration and greater runoff, in terms of overall mass balance, leading to a higher temperature, but lower relative humidity. Heat index and relative humidity were found to significantly vary between locations with different tree cover and neighborhood characteristics for the full study time period as well as for the top 10% of heat index days. This work demonstrates the need for high-resolution climate data and the use of additional measures beyond temperature to understand urban neighborhood exposure to extreme heat, and expresses the importance of considering vulnerability differences among residents when analyzing neighborhood-scale impacts.

Establishment and performance of an experimental green roof under extreme climatic conditions

Green roofs alter the surface energy balance and can help in mitigating urban heat islands. However, the cooling of green roofs due to evapotranspiration strongly depends on the climatic conditions, and vegetation type and density. In the Southern Central Plains of the United States, extreme weather events, such as high winds, heat waves and drought conditions pose challenges for successful implementation of green roofs, and likely alter their standard performance. The National Weather Center Experimental Green Roof, an interdisciplinary research site established in 2010 in Norman, OK, aimed to investigate the ecological performance and surface energy balance of green roof systems. Starting in May 2010, 26 months of vegetation studies were conducted and the radiation balance, air temperature, relative humidity, and buoyancy fluxes were monitored at two meteorological stations during April-October 2011. The establishment of a vegetative community trended towards prairie plant dominance. High mortality of succulents and low germination of grasses and herbaceous plants contributed to low vegetative coverage. In this condition succulent diversity declined. Bouteloua gracilis and Delosperma cooperi showed typological dominance in harsh climatic conditions, while Sedum species experienced high mortality. The plant community diversified through volunteers such as Euphorbia maculate and Portulaca maculate. Net radiation measured at a green-roof meteorological station was higher than at a control station over the original, light-colored roofing material. These findings indicate that the albedo of the green roof was lower than the albedo of the original roofing material. The low vegetative coverage during the heat and drought conditions in 2011, which resulted in the dark substrate used in the green roof containers being exposed, likely contributed to the low albedo values. Nevertheless, air temperatures and buoyancy fluxes were often lower over the green roof indicating that higher evapotranspiration rates compensated for the higher net radiation at the green roof.

Developing resilient green roofs in a dry climate

Living roofs are an emerging green infrastructure technology that can potentially be used to ameliorate both climate change and urban heat island effects. There is not much information regarding the design of green roofs for dry climates and so the aim of this study was to develop low maintenance and unfertilized green roofs for a dry climate. This paper describes the effects of four important elements of green roofs namely slope, depth, growing media and plant species and their possible interactions in terms of plant growth responses in a dry climate. Sixteen medium-scale green roofs were set up and monitored during a one year period. This experiment consisted of twelve vegetated platforms and four non-vegetated platforms as controls. The design for the experiment was a split-split-plot design in which the factors Slope (1° and 25°) and Depth (100mm, 300 mm) were randomized to the platforms (main plots). Root depth and volume, average height of plants, final dry biomass and ground cover, relative growth rate, final dry shoot-root ratio, water use efficiency and leaf succulence were studied during a twelve month period. The results showed little growth of the plants in media type A, whilst the growth was significant in both media types B and C. On average, a 90% survival rate of plants was observed. Also the growth indices indicated that some plants can grow efficiently in the harsh environment created by green roofs in a dry climate. The root growth pattern showed that retained water in the drainage layer is an alternative source of water for plants. It was also shown that stormwater can be used as a source of irrigation water for green roofs during six months of the year at the study site. In summary, mild sloping intensive systems containing media type C and planted with either Chrysocephalum apiculatum or Disphyma crassifolium showed the best performance.

A glossary for biometeorology

Here we present, for the first time, a glossary of biometeorological terms. The glossary aims to address the need for a reliable source of biometeorological definitions, thereby facilitating communication and mutual understanding in this rapidly expanding field. A total of 171 terms are defined, with reference to 234 citations. It is anticipated that the glossary will be revisited in coming years, updating terms and adding new terms, as appropriate. The glossary is intended to provide a useful resource to the biometeorology community, and to this end, readers are encouraged to contact the lead author to suggest additional terms for inclusion in later versions of the glossary as a result of new and emerging developments in the field.