Surface urban heat islands (SUHIs) are present in all cities, derived from their thermal properties. While looking at the spatiotemporal variability of land surface temperature (LST), there is still ...a gap in understanding patterns of change. In this paper, we analysed diurnal and nocturnal annual mean LST trends in continental (Beijing), temperate (Mexico City and Santiago), and arid (Cairo, Hyderabad, and Riyadh) cities employing 1 km MODIS data (2003–2019). Each time-series was assessed with the structure of a space-time cube. Hot and cold spots were detected for each year and the LST trends were analysed. Each pixel was classified into different space-time LST trends and their SUHIs were estimated. Cities exhibit trends of increasing temperatures in cold and hot spots for diurnal and nocturnal data. Temperatures are increasing faster in hot spots for diurnal and in cold spots for nocturnal scenes. Steady hot spots and warming hot spots exhibit the highest SUHIs for day and night. Our approach provides a framework to empirically delineate the spatial intraurban heterogeneity of LST patterns over time. This spatially explicit information provides insights into urban areas requiring heat mitigation strategies and can be used to monitor the performance of measures already implemented for climate adaptation.
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•LST trends were analysed for six cities employing space-time data cubes (2003–2019).•Spatial heterogeneity of space-time LST trends is high but follows clustered patterns.•LST is increasing faster in hot spots for diurnal and cold spots for nocturnal data.•Cold spots where cities expanded present low SUHI but are in a warming process.•Highest SUHI correspond to steady hot and lowest to steady cold spots.
Associated with rapid urbanization and escalation of bushfire events, Sydney has experienced significant air quality degradation in the XXI century. In this study, we present a 15-year retrospective ...analysis on the influence of individual meteorological factors on major air pollutants (NO2, O3, PM10 and PM2.5) at 14 different sites in Greater Sydney and Illawarra. By applying a newly developed “zooming in” approach to long-term ground-based data, we disclose general, seasonal, daily and hourly patterns while increasing the level of spatial associativity. We provide evidence on the pivotal role played by urbanization, sprawling dynamics, global warming and bushfires on local meteorology and air pollution. We strike associations between temperature and O3, both as average trends and extremes, on account of increasing heat island effects. The role of wind in a coastal-basin environment, influenced by a vast desert biome inland, is investigated. A steady trend towards stagnation is outlined, boosted by enhanced urban roughness and intensified heat island circulation. Relative humidity is also crucial in the modulation between NO2 and O3. With a sharp tendency towards drier and hotter microclimates, NO2 levels dropped by approximately 50% over the years at all locations, while O3's median levels almost doubled in the last 10 years. Further, O3 and PMs shifted towards more frequent extreme events, strongly associated with the exacerbation of bushfire events. Such results suggest an urgent need to prioritize emission control, building air tightness improvement and urban heat mitigation, towards a future-proof governance in Sydney and similar regions in the world.
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•15-Year meteorological and pollution data at 14 sites in Sydney are statistically analyzed.•NO2 reductions around 50% are countervailed by doubled O3 contents.•Temperature and O3 are strongly correlated on account of increasing heat island effects.•Wind exhibits a significant non-linear impact on local air quality.•A clear trend towards hotter, drier and more stagnant conditions is outlined.
Street trees are more and more regarded as an effective measure to reduce excessive heat in urban areas. However, the vast majority of mesoscale urban climate models do not represent street trees in ...an explicit manner and, for example, do not take the important effect of shading by trees into account. In addition, urban canopy models that take interactions of trees and urban fabrics directly into account are usually limited to the street or neighbourhood scale and hence cannot be used to analyse the citywide effect of urban greening. In order to represent the interactions between street trees, urban elements and the atmosphere in realistic regional weather and climate simulations, we coupled the Building Effect Parameterisation with Trees (BEP-Tree) vegetated urban canopy model and the Consortium for Small-scale Modeling (COSMO) mesoscale weather and climate model. The performance and applicability of the coupled model, named COSMO-BEP-Tree, are demonstrated over the urban area of Basel, Switzerland, during the heatwave event of June–July 2015. Overall, the model compared well with measurements of individual components of the surface energy balance and with air and surface temperatures obtained from a flux tower, surface stations and satellites. Deficiencies were identified for nighttime air temperature and humidity, which can mainly be traced back to limitations in the simulation of the nighttime stable boundary layer in COSMO. The representation of street trees in the coupled model generally improved the agreement with observations. Street trees produced large changes in simulated sensible and latent heat flux, and wind speed. Within the canopy layer, the presence of street trees resulted in a slight reduction in daytime air temperature and a very minor increase in nighttime air temperature. The model was found to realistically respond to changes in the parameters defining the street trees: leaf area density and stomatal conductance. Overall, COSMO-BEP-Tree demonstrated the potential of (a) enabling city-wide studies on the cooling potential of street trees and (b) further enhancing the modelling capabilities and performance in urban climate modelling studies.
Sustainable transformation is hampered by conflicting goals. Here we examine how goal conflicts are handled in planning practice, focusing on processes around municipal climate and sustainability ...governance. We investigate local manifestations of goal conflicts between transport and land use planning and emissions reductions in three Norwegian cities, using document analysis, interviews and observation. We find that governance actors handle goal conflicts through what we term strategies of displacement. We identify three such strategies: temporal, sectorial and scalar. The research contributes to explaining how and why goal conflicts persist in planning practice.
Cities are critical sites for climate action. Population and infrastructure are concentrated in urban areas and their susceptibility to climate change impacts makes them a pivotal place to embark on ...adaptation plans and strategies. In the Fifth Assessment Report (AR5) the Intergovernmental Panel on Climate Change (IPCC) affirms that urban adaptation allows sustainable development and resilience. However, without evidence, this affirmation fails to acquire credibility and objectivity. As an attempt to provide the evidence for the assertion, this study examines the current actions in urban centers to determine if there is an alignment between adaptation and development. The study employs text mining techniques to analyze 400 urban project descriptions from Cities100 reports (2015–2019) of the C40 network. With Latent Dirichlet Allocation (LDA), a machine learning algorithm for topic model analysis, the study identifies 17 major topics. Using multidimensional scaling and cluster analysis to further characterize the findings, it finds an alignment of adaptation with urban sustainable and resilient development in several major cities. In this way, the paper makes a contribution to a global understanding of urban adaptation as well as demonstrates a way of adopting the grey literature into the urban adaptation studies.
•Adaptation is one of the key themes of urban projects for sustainability.•Cities are taking adaptation actions for sustainable development.•Urban adaptation actions are closely related with increasing green space.•Topic modeling on grey literature helps tackle the limitation of urban adaptation data.
In this work, the climatic impacts of modifying urban surface characteristics are examined for the medium-sized city of Vantaa, Finland, in the current climate and in a projected future climate of ...2040–2069. In simulations with the SURFEX air-surface interaction model with a horizontal resolution of 500 m, the fraction of green spaces and relatively sparsely built suburban-type land use was increased at the expense of more densely built commercial and industrial areas. The influence of this land use intervention was found to be rather modest but comparable to the effects of the expected climate change under the RCP8.5 greenhouse gas scenario. For temperature, the climate change is the dominating effect, while wind speed is mainly controlled by surface characteristics. For relative humidity, climate change and the imposed intervention are of comparable importance. The results of this sensitivity study are intended to support policy makers by assessing the potential impact of altering the urban layout in order to improve thermal comfort or as a countermeasure to climate warming in a high-latitude city.
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•Altering urban characteristics has a climatic impact even in a sparsely built city.•The share of green spaces and suburban-type land use was increased in simulations.•The intervention cools the town and the local climate becomes more humid and windy.•Global climate change dominates over the intervention, except for wind.
Renewable energy sources have emerged globally as a key lever to ensure energy security and to promote climate mitigation. Cities need to exploit this energy transition, but how they are building ...their strategies and actions is undetermined. A new dataset, collected through the European 100 Climate-Neutral and Smart Cities Mission, offers unique insights on the 362 cities which expressed the ambition to reach climate neutrality by 2030. Insights include their level of preparedness, ambition, capacity and the risks envisaged in the pursuit of zero-emission and greener futures. This study focuses in particular on the role of renewable energy across high greenhouse gas emitting sectors in cities (e.g. buildings, mobility, waste and industry). It analyses i) the status quo for renewable energy generation, consumption, and policymaking, ii) the key measures to enhance and upscale renewable energy deployment in the near future, and iii) how policies and relevant instruments will evolve to curb emissions and accelerate the energy transition. The insights that emerge from the analysis are discussed in relation to existing evidence, to inform future research strands and forms of assistance for cities. Overall, for cities to deliver on large renewable projects, efforts need to be intensified, barriers need to be lifted and multi-governance approaches must be operationalised.
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•The role of renewable energy in city plans for climate neutrality is examined.•A novel and comprehensive dataset for 362 cities is used to perform the analysis.•City policies, instruments, key measures, and scalable interventions are discussed.•Conclusions and recommendations are outlined to inform future research.
This study developed a top-down method for estimating global anthropogenic heat emission (AHE), with a high spatial resolution of 30 arc-seconds and temporal resolution of 1 h. Annual average AHE was ...derived from human metabolic heating and primary energy consumption, which was further divided into three components based on consumer sector. The first and second components were heat loss and heat emissions from industrial sectors equally distributed throughout the country and populated areas, respectively. The third component comprised the sum of emissions from commercial, residential, and transportation sectors (CRT). Bulk AHE from the CRT was proportionally distributed using a global population dataset, with a radiance-calibrated nighttime lights adjustment. An empirical function to estimate monthly fluctuations of AHE based on gridded monthly temperatures was derived from various Japanese and American city measurements. Finally, an AHE database with a global coverage was constructed for the year 2013. Comparisons between our proposed AHE and other existing datasets revealed that the problem of overestimation of AHE intensity in previous top-down models was mitigated by the separation of energy consumption sectors; furthermore, the problem of AHE underestimation at central urban areas was solved by the nighttime lights adjustment. A strong agreement in the monthly profiles of AHE between our database and other bottom-up datasets further proved the validity of the current methodology. Investigations of AHE for the 29 largest urban agglomerations globally highlighted that the share of heat emissions from CRT sectors to the total AHE at the city level was 40–95%; whereas that of metabolic heating varied with the city's level of development by a range of 2–60%. A negative correlation between gross domestic product (GDP) and the share of metabolic heating to a city's total AHE was found. Globally, peak AHE values were found to occur between December and February, while the lowest values were found around June to August. The northern mid-latitudes contributed most to the global AHE.
•A global database of anthropogenic heat emission (AHE) with high spatial resolution was constructed using a top-down approach.•Annual average AHE was estimated from four heating components, based on different sectors of energy consumption.•A population-adjustment using nighttime light was created to improve estimating AHE spatial variability in urban areas.•A sensitivity function of AHE relative to temperature was derived to provide a way to evaluate AHE monthly variability globally.
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 (UC2) 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.
Urban environmental issues have a negative impact on urban quality of life in cities. Erzurum city is a very special place in the world because it has a very high altitude, harsh, long winter period, ...and high air pollution that affects the human thermal comfort sensation and the quality of life negatively. The purpose of this research is to assess the effects of different landscapes and built environmental patterns on thermal comfort and air pollution. The urban microclimate factors were recorded by field measurement weather stations and the air pollution data was collected from Turkish government monitoring stations. The thermal comfort was evaluated by the Physiologically Equivalent Temperature (PET°C) index. The results show that there is an extreme variation in the city's climate during the year. In August, the maximum temperature is 33.0 °C and the maximum average temperature is 23.0 °C, while in December the lowest temperature is −35.0 °C and the maximum average temperature is −11.4 °C. At the Ata Botanical Garden (wooded area) and in rural open areas, the temperature is 13.0 °C lower in the summer and 10.0 °C–15.0 °C lower in the winter than in urban areas. The highest average values (PET°C) were found in the city center (11.2 °C) and wooded areas (10.0 °C), while the lowest average values of PET were found in the open rural area (4.7 °C) in both seasons. Seasonal wetland (7.1 °C) and industrial (9.6 °C) areas experienced moderate thermal comfort. The Taşhan area, located near the city center and surrounded by an industrial zone, is the most polluted in the city. The statistical analysis shows that there is a significant correlation between the Ozone (O3) and the PET °C values, with R2 = 0.47 in this area. The wooded areas were found to be advantageous in raising thermal comfort and lowering air pollution.
•The city center and wooded area experienced the best thermal comfort in the summer and winter months.•Wetland and industrial areas provide a moderate thermal comfort level in cold regions.•A significant correlation was found between the PET thermal index and Ozone (O3) pollution.•A compact environment in the city center with industrial activities emits a high amount of polluting gases.
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