Abstract This work presents a high‐resolution spatiotemporal analysis of the urban heat island (UHI) effect in Swiss cities during the last 6 years. The entire alpine country is simulated at once ...using the COSMO model at 1.1 km resolution, validated against a dense national measurement network. Additionally, the bulk parametrisation TERRA URB is used to model the dynamical and thermal effects of urban areas. The resulting data allows us to perform the first comprehensive analysis over the entire Switzerland, with a focus on the UHI effect with intra‐urban and across cities comparisons, and to report on the current state of urban warming. Despite the medium‐small size of the cities, the UHI is of considerable magnitude especially when considering peak values in ideal weather conditions. The present results confirm previous analyses performed for individual cities, and shed new light on the country‐wide picture by highlighting features such as the marked seasonality of the UHI intensity as well as the influence of local climate and topographical features on the urban climate. A thorough discussion is also presented highlighting the absence of simple relationships between UHI intensity and bulk city parameters and weather patterns.
The land surface temperature (LST) of urban streets is significantly influenced by the surrounding urban environment. In the cold areas of northern China, this influence exhibits a seasonal pattern. ...Currently, in areas with noticeable seasonal variations, the coupling effects of urban elements on the annual stability of street LST remain unclear. This study developed a new metric, Normalized Winter-Summer Land Surface Temperature Difference, to measure the year-round LST stability of campus streets. Three key urban elements affecting street-level LST in winter and summer were identified: building, vegetation, and land. The influencing characteristics for winter and summer LST were quantified and ranked respectively. The study reveals that the green space ratio dominates summer LST, while fraction vegetation coverage, leaf area index and average building height dominate winter LST. We found that morphological characteristics of buildings and vegetation cannot fully explain the impact of the urban physical environment on street-level LST. For winter street LST studies, greater emphasis should be placed on non-morphological characteristics and land. Based on the impact mechanisms and critical thresholds of key features in winter and summer, this study establishes an interpretable spatial classification method. By assigning seasonal weights to influencing features, it provides comprehensive design strategies that consider both winter and summer features to enhance annual LST stability and climate resilience in urban spaces facing extreme meteorological conditions.
•A new metric for assessing LST stability of streets in cold areas was developed.•Design strategies to improve annual street LST stability were proposed.•Morphological features can't fully explain the urban elements' impact on street LST.•Street LST research should emphasis non-morphological characteristics, especially in winter.•Consider non-morphological characteristics in street LST studies to avoid potential biases.
O aumento da temperatura da superfície tem causado preocupação mundial, principalmente porque as modificações do ambiente urbano interferem consideravelmente no conforto ambiental. O desenvolvimento ...das cidades está frequentemente marcado pela remoção de cobertura vegetal, movimentação de terra e impermeabilização do solo. Para investigar um processo de urbanização acentuado e seus efeitos no microclima, estudou-se o município de Rio Verde, estado de Goiás, Brasil, no período de 1985 a 2019. Objetivou-se com este estudo, avaliar espaço-temporalmente as mudanças do uso e ocupação solo e seus impactos na temperatura da superfície no Município. Para isso, desenvolveu-se uma condição embasada num algoritmo de decisão hierárquica, para classificar especificamente a distribuição espacial de solos de Cerrado urbano. Foi utilizado dados extraídos de imagens orbitais dos satélites Landsat-5 e Landsat-8 no período de 1985 a 2019. Dentre os resultados, detectou-se o aumento de camadas de superfície termicamente ativas, resultando em alterações na temperatura da superfície demonstrando que a intensidade das ilhas de calor é superior em áreas de solos impermeabilizados. Este estudo por fim concluiu-se, que a expansão urbana, assim como os demais parâmetros ambientais ocasionados por esta, foram a principal força motriz e causa dessas modificações e impactos no microclima observados no município. Nesse sentido, as mudanças do uso e ocupação do solo resultou em alterações no comportamento térmico superficial ocasionado principalmente pela transformação do uso do solo.
•Radiation, evapotranspiration, and roughness effects of urban trees are separated.•Tree-radiation interaction increases/decreases urban canopy air/surface temperature.•Tree evapotranspirative ...cooling is limited at high vapour pressure deficits.•Dense tree canopies can reduce aerodynamic roughness and increase air temperature.•Night-time tree effects are variable due to differences in atmospheric stability.
Increasing urban tree cover is an often proposed mitigation strategy against urban heat as trees are expected to cool cities through evapotranspiration and shade provision. However, trees also modify wind flow and urban aerodynamic roughness, which can potentially limit heat dissipation. Existing studies show a varying cooling potential of urban trees in different climates and times of the day. These differences are so far not systematically explained as partitioning the individual tree effects is challenging and impossible through observations alone. Here, we conduct numerical experiments removing and adding radiation, evapotranspiration, and aerodynamic roughness effects caused by urban trees using a mechanistic urban ecohydrological model. Simulations are presented for four cities in different climates (Phoenix, Singapore, Melbourne, Zurich) considering the seasonal and diurnal cycles of air and surface temperatures.
Results show that evapotranspiration of well-watered trees alone can decrease local 2 m air temperature at maximum by 3.1– 5.8 °C in the four climates during summer. Further cooling is prevented by stomatal closure at peak temperatures as high vapour pressure deficits limit transpiration. While shading reduces surface temperatures, the interaction of a non-transpiring tree with radiation can increase 2 m air temperature by up to 1.6 – 2.1 °C in certain hours of the day at local scale, thus partially counteracting the evapotranspirative cooling effect. Furthermore, in the analysed scenarios, which do not account for tree wind blockage effects, trees lead to a decrease in urban roughness, which inhibits turbulent energy exchange and increases air temperature during daytime. At night, single tree effects are variable likely due to differences in atmospheric stability within the urban canyon. These results explain reported diurnal, seasonal and climatic differences in the cooling effects of urban trees, and can guide future field campaigns, planning strategies, and species selection aimed at improving local microclimate using urban greenery.
Urban populations are expected to increase by 2-3 billion by 2050, but we have limited understanding of how future global urban expansion will affect urban heat island (UHI) and hence change the ...geographic distributions of extreme heat risks. Here we develop spatially explicit probabilistic global projections of UHI intensification due to urban land expansion through 2050. Our projections show that urban land areas are expected to expand by 0.6-1.3 million km2 between 2015 and 2050, an increase of 78%-171% over the urban footprint in 2015. This urban land expansion will result in average summer daytime and nighttime warming in air temperature of 0.5 °C-0.7 °C, up to ∼3 °C in some locations. This warming is on average about half, and sometimes up to two times, as strong as that caused by greenhouse gas (GHG) emissions (multi-model ensemble average projections in Representative Concentration Pathway 4.5). This extra urban expansion-induced warming, presented here, will increase extreme heat risks for about half of the future urban population, primarily in the tropical Global South, where existing forecasts already indicate stronger GHG emissions-warming and lack of adaptive capacity. In these vulnerable urban areas, policy interventions to restrict or redistribute urban expansion and planning strategies to mitigate UHIs are needed to reduce the wide ranges of impacts on human health, energy system, urban ecosystem, and infrastructures.
Urbanization is one of the biggest social transformations of modern time, driving and driven by multiple social, economic, and environmental processes. The impacts of urbanization on the environment ...are profound, multifaceted and are manifested at the local, regional, and global scale. This article reviews recent advances in conceptual and empirical knowledge linking urbanization and the environment, focusing on six core aspects: air pollution, ecosystems, land use, biogeochemical cycles and water pollution, solid waste management, and the climate. We identify several emerging trends and remaining questions in urban environmental research, including (
a
) increasing evidence on the amplified or accelerated environmental impacts of urbanization; (
b
) varying distribution patterns of impacts along geographical and other socio-economic gradients;
(
c
) shifting focus from understanding and quantifying the impacts of urbanization toward understanding the processes and underlying mechanisms; (
d
) increasing focus on understanding complex interactions and interlinkages among different environmental, social, economic, and cultural processes; and (
e
) conceptual advances that call for articulating and using a systems approach in cities. In terms of governing the urban environment, there is an increasing focus on public participation and coproduction of knowledge with stakeholders. Cities are actively experimenting toward sustainability under a plethora of guiding concepts that manifests their aspirational goals, with varying levels of implementation and effectiveness.
•Three regulating ecosystem services (ES) provided by street trees are quantified.•Associations between street tree ES and five socioeconomic variables are analyzed.•Street tree ES are positively ...associated to the distribution of vulnerable age groups.•Street trees play a redistributive role in terms of regulating ES provision in Barcelona.•Just green infrastructure planning should carefully consider street tree benefits.
Street trees are an important component of green infrastructure in cities, providing multiple ecosystem services (ES) and hence contributing to urban resilience, sustainability and livability. Still, access to these benefits may display an uneven distribution across the urban fabric, potentially leading to socio-environmental inequalities. Some studies have analyzed the distributional justice implications of street tree spatial patterns, but generally without quantifying the associated ES provision. This research estimated the amount of air purification, runoff mitigation and temperature regulation provided by circa 200,000 street trees in Barcelona, Spain, using the i-Tree Eco tool. Results were aggregated at neighborhood (n = 73) and census tract (n = 1068) levels to detect associations with the distribution of five demographic variables indicating social vulnerability, namely: income, residents from the Global South, residents with low educational attainment, elderly residents, and children. Associations were evaluated using bivariate, multivariate and cluster analyses, including a spatial autoregressive model. Unlike previous studies, we found no evidence of a significant and positive association between the distribution of low income or Global South residents and a lower amount of street tree benefits in Barcelona. Rather, higher ES provision by street trees was associated with certain types of vulnerable populations, especially elderly citizens. Our results also suggest that street trees can play an important redistributive role in relation to the local provision of regulating ES due to the generally uneven and patchy distribution of other urban green infrastructure components such as urban forests, parks or gardens in compact cities such as Barcelona. In the light of these findings, we contend that just green infrastructure planning should carefully consider the distributive implications associated with street tree benefits.
Climate change actions in cities worldwide are driving deep changes in urban governance. We ask whether new capacities for transformative climate governance are emerging in two cities that have ...experimented with urban climate governance: Rotterdam, the Netherlands, and New York City (NYC), United States. Transformative climate governance creates the conditions for developing integrated and innovative climate mitigation and adaptation policies and interventions that respond to and shape urban transformation dynamics and contribute to sustainability and resilience. The comparison of capacities for transformative climate governance in Rotterdam and NYC offers insights into the emerging features of urban climate governance vis-à-vis existing urban governance regimes: how urban climate governance is driven and delivered, what new governance conditions emerge, and whether these conditions enable transformative climate governance. In both cities, an integrated, experimental and inclusive approach to climate governance is emerging, which crosses multiple policy sectors and domains (e.g. transport, energy, health, justice), involves a variety of actors and facilitates innovative solutions. Envisioning, long-term goal and knowledge integration, experimentation and tapping into coalitions for change help to provide the basis (including guiding principles, urgency, actor networks, innovative solutions) for transformative climate governance. However, these transformative approaches tend to be still subordinate to business-as-usual interests and policy and planning approaches, which favour isolated, incremental and short-term responses. The challenge for strengthening transformative climate governance will be to develop rigorous institutional and organisational conditions that decisively stipulate a prioritisation of climate change across scales and sectors, provide action mandates and enable wider coordination, collaboration and learning.
•Climate governance activities in cities drive deep changes in urban governance.•Transformative climate governance (TCG) supports desirable urban transformations.•Capacities for TCG manifest in new institutional, knowledge and network conditions.•Visioning, goal and knowledge integration and experimentation create TCG capacities.•Top-down institutional and organisational conditions need to be strengthened for TCG.
Although the urban heat island (UHI) phenomenon is more commonly studied in summer, its influence is also important in winter. In this study, the authors focused on the winter UHI in Ljubljana ...(Slovenia) and its impact on the urban population, as well as in comparison with a UHI study from 2000. Through a combination of mobile and stationary temperature measurements in different parts of the city, the winter intensity of the UHI in Ljubljana was studied in a dense spatial network of measurements. It was found that the intensity of the winter UHI in Ljubljana decreases as winters become warmer and less snowy. The results showed that the winter UHI in Ljubljana intensifies during the night and reaches the greatest intensity at sunrise. During the winter radiation type of weather, the warmest part of Ljubljana reaches an intensity of 3.5 °C in the evening. In total, 22% of the urban area is in the evening UHI intensity range of 2–4 °C, and 65% of the urban population lives in this range. In the morning, the UHI in Ljubljana has a maximum intensity of 5 °C. The area of >4 °C UHI intensity covers 7% of the urban area, and 28% of the total urban population lives in this area. Higher temperatures in urban centers in winter lead to a longer growing season, fewer snow cover days, lower energy consumption and cold stress, and lower mortality from cold-related diseases compared to the colder periphery.
A cidade de Três Lagoas nos últimos anos teve seu crescimento acelerado com a industrialização e a implantação da silvicultura de eucalipto, intensificando sua urbanização e trazendo os problemas ...ambientais decorrentes desse crescimento. Com base nisso, o presente estudo teve por objetivo a análise de dados climatológicos noturnos de Três Lagoas/MS, nos meses de fevereiro a junho de 2019, embasado na teoria do Sistema Clima Urbano (S.C.U.) de Monteiro (1975), e utilizando-se da classificação da intensidade e magnitude da ilha de calor de Fernández García (1996). Os procedimentos metodológicos adotados, foram a mensuração da temperatura do ar em 2 pontos fixos (centro urbano e rural próximo), no período de 02 de fevereiro a 30 de junho de 2019, nos horários das 20 h às 06 h, e seu posterior tratamento em softwares específicos. Os resultados evidenciaram que durante o período analisado, observou-se a formação de ilhas de calor noturnas em todos os meses, sendo de até 10,7ºC em fevereiro, 5,8°C em março, 6,2ºC em abril, 7,1ºC em maio e 7,7ºC em junho. Tais resultados demonstraram ilhas de calor classificadas como de muito forte magnitude. Deste modo, acredita-se que o presente estudo pode subsidiar ações de planejamento urbano para tornar as cidades e os assentamentos humanos inclusivos, seguros e resilientes. Além disso, frisa-se que medidas de mitigação devem ser adotadas pelo poder público, pois a cidade localiza-se numa posição geográfica que lhe impõe a tropicalidade, ambiente natural de altas temperaturas e a urbanização sem planejamento adequado pode intensificar a sensação de desconforto térmico para a população.
Ces dernières années, la ville de Três Lagoas a connu une croissance accélérée en raison de son industrialisation récente et de la plantation d’eucalyptus, intensifiant alors le processus d’urbanisation et entrainant des problèmes environnementaux. Cette étude a pour objectif d’analyser les données climatologiques nocturnes de Três Lagoas/MS, entre les mois de février et juin 2019, dans la perspective de la théorie du Système Climat Urbain de Monteiro (1975), grâce à la classification de l’intensité et de la magnitude des ilots de chaleur de Fernandez Garcia (1996). La méthodologie adoptée a consisté en des mesures de température de l’air en 2 points fixes (centre urbain et rural proche), du 02 février au 30 juin 2019, de 20h à 6h, suivi de leur traitement au sein de programmes spécifiques. Les résultats ont permis d’identifier la formation d’ilots de chaleur nocturne, sur l’ensemble de la période étudiée, en raison de 10,7°C en février, 5,8°C en mars, 6,2°C en avril, 7,1°C en mai et 7,7°C en juillet. Ces résultats démontrent des ilots de chaleurs de magnitudes élevées. Ainsi, le présent travail peut contribuer à orienter les actions d’aménagement urbain afin de rendre les villes et hameaux plus inclusifs, sûrs et résilients. De plus, des moyens en faveur de la mitigation doivent être engagés par le pouvoir public, de par la localisation géographique même de la ville où la tropicalité y est imposée, contenant des environnements naturels à fortes températures et une urbanisation sans aménagement territorial adapté, pouvant intensifier la sensation d’inconfort thermique de la population.
Três Lagoas, in the state of Mato Grosso do Sul (MS) and like other Brazilian cities, has seen its growth accelerated in recent years with industrialization and the implementation of eucalyptus forestry, intensifying its urbanization and bringing the problems arising from this growth. The present study aims at analyzing daily nocturnal climatological data from Três Lagoas from February 2nd to June 30th, 2019, based on the theory of the Urban Climate System (S.C.U.) by Monteiro (1975). We use the intensity classification from the heat island of Fernández García (1996). The methodological procedures adopted were the daily measurement of air temperature at 2 fixed points (urban center and nearby rural), from 8 pm to 6 am, and its subsequent treatment in specific software. The results show that during the analyzed period, the formation of nocturnal heat islands was observed in all months, being up to 10.7ºC in February, 5.8ºC in March, 6.2ºC in April, 7.1ºC in May and 7.7ºC in June. Such results show the classification of heat islands of very strong magnitudes. Thus, it is believed that the present study can support urban planning actions to make cities and human settlements more inclusive, safer, and more resilient. In addition, it is emphasized that mitigation measures must be adopted by the public authorities. Três Lagoas, which is in a geographical position that imposes tropicality, a natural environment of high temperatures and urbanization. Lacking adequate planning can intensify the feeling of thermal discomfort for a population.
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