Intra-urban Temperature Differences Research Articles

A comprehensive methodology for assessing outdoor thermal comfort in touristic city of Porto (Portugal)

Urban tourism's impact on intra-urban temperature differences and the latter's influence on thermal comfort in public space, in a context of climate change, is still not clear. When it comes to urban tourism, few are the studies which assess human thermal comfort in the form of visual and cartographic representation. This paper seeks to fill this gap by obtaining data through measurement campaigns carried out in a motor vehicle during the summers and winters of 2019 and 2020, in a total of 27 nights and 7 afternoons. The Portuguese city of Porto was the selected destination. It revealed very useful in identifying the intra-urban temperature differences and the patterns of human thermal comfort in different days of the year. Based on the mobile measurement campaign carried out in the aforementioned period, the main thermal patterns and implications to thermal comfort in the central area of Porto were summarized. There is a multiplicity of situations of thermal comfort and spatial variations of discomfort due to cold and heat stress. These conditions are particularly relevant during the summer season, when the urban heat island intensity can exceed 3.0 °C. The proposed methodology could be very useful for researchers in the field of tourism climatology and policymakers, given that it contributes with adaptive measures regarding the tourism sector in the face of intense vulnerability to climate change.

Evaluation and application of a low-cost measurement network to study intra-urban temperature differences during summer 2018 in Bern, Switzerland

The understanding of intra-urban air temperature variations is crucial to assess strategies for cities' adaptation to impacts of present and future anthropogenic climate change. Depending on extensive measurement networks, high-resolution air temperature measurements in urban environments are challenging due to high instrumentation and maintenance costs. Here, we present a low-cost measurement device (LCD) consisting of a temperature logger and a custom-made, naturally ventilated radiation shield. Besides intercomparisons with automated weather stations (AWS) at three reference sites during record-dry summer 2018, we tested the potential of the devices using a network of 79 LCDs to assess the intra-urban variability of urban heat island (UHI) patterns in the city of Bern, Switzerland. We found positive mean measurement biases between LCDs and AWS of 0.61 to 0.93 K (RMSE: 0.78 to 1.17 K) during daytime, of which up to 82.8% of the variance could be explained statistically by solar irradiance (radiative heating) and wind speed (insufficient ventilation). During night, average measurement biases were markedly lower and eventually negative with −0.12 to 0.23 K (RMSE: 0.19 to 0.34 K). Our results highlight the importance of sensor intercomparisons being conducted at multiple locations with differing urban land-cover, structure, and metabolism given that biases varied considerably between the reference sites. Data retrieved by the city-wide measurement network showed that the LCD approach is well suited for the analysis of spatiotemporal UHI patterns during night and adds considerable value compared to the few existing AWS in detecting fine-scale air temperature variability. In conclusion, the current LCD measurement approach represents a valuable option for cost-effective analyses of urban air temperature variability across multiple scales, which may be of particular value for the development, appliance, and monitoring of adaptation strategies to climate change in cities with restricted financial resources.

Trends and irregular variation of spatial temperature differences in the high-latitude coastal city of Turku, Finland

Spatio-temporal dynamics of urban heat island (UHI) and other spatial temperature variations were studied for a 17 yr period (2002-2018) in the mid-sized (193000 inhabitants in 2019) coastal city of Turku in south-western Finland. The study was based on GIS data and 30 min interval air temperature observations from 52 observation sites in the city and its surroundings. Correlation and regression analyses, image interpretation and various GIS methods were used to investigate temperature dynamics and associated factors on a diurnal, monthly and seasonal basis. The results showed relative cooling and warming trends of certain areas as well as fluctuating and random variation of the coldest and warmest regions, respectively. Relative cooling trends were observed in semi-urban and urban areas that remained unchanged during the study period. Relative warming trends were most common in semi-urban areas where urbanization and construction of new buildings occurred rapidly. Fluctuating variation was mainly related to variation in weather conditions, especially the severity of winter and related sea-ice extent on the archipelago south-west of the city. The UHI intensity showed a slight, albeit statistically significant, intensifying trend of 0.11°C per decade. Our findings demonstrate the dynamic nature of spatio-temporal intra-urban temperature differences, a fact that should more actively be taken into account in climate-related urban planning in general.

The urban climate of Ghent, Belgium: A case study combining a high-accuracy monitoring network with numerical simulations

As urban environments have a specific climate that poses extra challenges (e.g. increased heat stress during heat waves), gaining detailed insight into the urban climate is important. This paper presents the high-accuracy MOCCA (MOnitoring the City's Climate and Atmosphere) network, which is monitoring the urban climate of the city of Ghent since July 2016. The study illustrates the complementarity between modelling and observing the urban climate. Two different modelling approaches are used: 1 km resolution runs of the SURFEX land surface model and 100 m resolution runs of the computationally cheaper UrbClim boundary layer model. On the one hand, urban models are able to simulate the spatial variability of the urban climate. As such, these models serve as a tool to help deciding on the locations of the measurement stations. On the other hand, the MOCCA observations are used to validate the high-resolution urban model experiments for the summer (July-August-September) of 2016. Our results demonstrate that the models capture the nighttime intra-urban temperature differences, but they are not able to reproduce the observed daytime temperature differences which are determined by the micro-scale environment.

Effects of atmospheric stability and urban morphology on daytime intra-urban temperature variability for Glasgow, UK

This study investigates the joint effect of atmospheric conditions and urban morphology, expressed as the Sky View Factor (SVF), on intra-urban variability. The study has been carried out in Glasgow, UK, a shrinking city with a maritime temperate climate type, and findings could guide future climate adaptation plans in terms of morphology and services provided by the municipality to overcome thermal discomfort in outdoor settings. In this case, SVF has been used as an indicator of urban morphology. The modified Pasquill-Gifford-Turner (PGT) classification system was adopted for classifying the temperature monitoring periods according to atmospheric stability conditions. Thirty two locations were selected on the basis of SVF with a wide variety of urban shapes (narrow streets, neighbourhood green spaces, urban parks, street canyons and public squares) and compared to a reference weather station during a total of twenty three transects during late spring and summer in 2013. Maximum daytime intra-urban temperature differences were found to be strongly correlated with atmospheric stability classes. Furthermore, differences in air temperature are noticeable in urban canyons, with a direct correlation to the site's SVF (or sky openness) and with an inverse trend under open-air conditions.

Atmospheric Impacts on Daytime Urban Heat Island

Daytime urban heat island effects can be weak compared to night time and even reversed (as in the case of cool islands, where urban locations display lower temperatures than at a rural site), mostly due to shading effects from buildings, vegetation, and other possible obstructions. The study of the relationship between the sky-view factor, an indicator of urban geometry in terms of sky openness, and urban heat island intensity generally focus on night time periods; only a few report on the daytime effect of the SVF. Such effect will also vary according to background atmospheric conditions of the period of measurements. This article is a commentary on a recent publication by the authors on a study of diurnal intra-urban temperature differences in a location with Koeppen’s Cfb climate.

Interferências da forma urbana na dinâmica da temperatura intra-urbana

As perspectivas de mudanças climáticas e suas possíveis consequências recomendam o desenvolvimento de estratégias para mitigar problemas relacionados ao sobreaquecimento urbano. O presente estudo tem como objetivo examinar a interferência da forma urbana, aferida pela Fracção de Céu Visível (Sky View Factor, SVF), sobre as variações na temperatura intra-urbana na cidade de Glasgow, Reino Unido, uma cidade de clima frio. 49 pontos de medição foram locados no centro da cidade e foram desenvolvidas 31 campanhas de coleta de dados, durante a primavera e o verão de 2013. Para cobrir uma grande área dentro de um tempo relativamente curto, foi utilizado o método de ‘transecto’ com rotas pré-determinadas, a pé e de bicicleta. O software ArcGIS foi utilizado para visualização dos resultados. Os resultados indicam que a variação da diferença da temperatura intra-urbana está fortemente relacionada à estabilidade atmosférica, sugerindo que esta tem realmente um importante efeito nessa variação. O estudo conseguiu apontar ainda, conforme esperado, que a vegetação e os materiais de cobertura urbana desempenham um papel importante, interferindo no clima local. O conhecimento das interferências nas variações de temperatura local pode ser mais um aliado na elaboração de estratégias apropriadas para lidar com os problemas do sobreaquecimento urbano.

Analysis of nocturnal air temperature in districts using mobile measurements and a cooling indicator

The urban heat island phenomenon is generally defined as an air temperature difference between a city center and the non-urbanized rural areas nearby. However, this description does not encompass the intra-urban temperature differences that exist between neighborhoods in a city. This study investigates the air temperature dynamics of neighborhoods for meteorological conditions that lead to important urban heat island amplitude. Local climate zones (LCZs) have been determined in Nancy, France, and mobile screen-height air temperature measurements are performed using an instrumented vehicle. Initially, hourly measurements are performed within four different LCZs. These results show that air temperature within LCZ demonstrates a nocturnal cooling in two phases, i.e., a first phase between 1 to 3 h before sunset and 3 to 5 h after sunset, and a second phase from 3 to 5 h after sunset to sunrise. During phase 1, neighborhoods exhibit different cooling rate values and air temperature gaps develop between districts, while during phase 2, cooling rates tend to be analogous. Then, a larger meteorological data set is used to investigate these two phases for a selection of 13 LCZs. Normalized cooling rates are calculated between daytime measures and nighttime measures in order to quantify the air temperature dynamics of the studied areas during phase 1. Considering this indicator, three groups are emerging: Results indicate that the relative position of LCZ within the conurbation does not drive air temperature dynamics during phase 1. In addition, measures performed during phase 2 tend to illustrate that cooling rates are similar to all LCZ during this period.

Intra-Urban Air Temperature Distribution, Urban Heat Island and Thermal Comfort Implications in A Subtropical City

Unlike most of the Brazilian hot-humid cities, subtropical Curitiba experiences thermal discomfort due to cold during most of the year, with the coldest air temperature occurring in winter. Due to rapid urbanization, the Metropolitan Area has been faced with critical environmental problems. Urban microclimate patterns exhibit considerable variability; particular areas of the city alternate between cool islands and heat islands, resulting in different outdoor thermal comfort levels. The objective of this work is twofold: 1) to characterize intra-urban air temperature differences and their impact on outdoor thermal comfort in Curitiba; 2) to assess the yearlong Urban Heat Island (UHI) effect and its effect on indoor thermal comfort levels. For that, a series of independent measurements and field monitoring campaigns, both outdoors and indoors, were analyzed. Results point to a great variability in intra-urban temperature differences and derived outdoor comfort levels. With regard to predicted UHI effects in low-cost dwellings, indoor comfort due to heat was found to prevail over the year; the 'net effect' between heat stress in summer and cold stress in winter point towards a prevalence of heat stress indoors.

Quantifying the impact of land cover composition on intra-urban air temperature variations at a mid-latitude city.

The effects of land cover on urban-rural and intra-urban temperature differences have been extensively documented. However, few studies have quantitatively related air temperature to land cover composition at a local scale which may be useful to guide landscape planning and design. In this study, the quantitative relationships between air temperature and land cover composition at a neighborhood scale in Beijing were investigated through a field measurement campaign and statistical analysis. The results showed that the air temperature had a significant positive correlation with the coverage of man-made surfaces, but the degree of correlation varied among different times and seasons. The different land cover types had different effects on air temperature, and also had very different spatial extent dependence: with increasing buffer zone size (from 20 to 300 m in radius), the correlation coefficient of different land cover types varied differently, and their relative impacts also varied among different times and seasons. At noon in summer, ∼37% of the variations in temperature were explained by the percentage tree cover, while ∼87% of the variations in temperature were explained by the percentage of building area and the percentage tree cover on summer night. The results emphasize the key role of tree cover in attenuating urban air temperature during daytime and nighttime in summer, further highlighting that increasing vegetation cover could be one effective way to ameliorate the urban thermal environment.

Accounting for atmospheric stability conditions in urban heat island studies: The case of Glasgow, UK

We evaluate the effect of atmospheric stability on seasonal ambient temperature differences between a pair of urban and rural weather stations (Urban Heat Island effect) and day/night intra-urban differences between a set of temperature/relative humidity (T/RH) stations in Glasgow, UK. The purpose is to estimate the background atmospheric effects on urban-vs-rural (UHI) as well as intra-urban differences in temperatures so that the effect of urban morphology in terms of local sky view factor (SVF) on local climate can be more clearly observed in high latitude cities such as Glasgow. For the UHI analysis, we used a pair of fully equipped weather stations and for the analysis of intra-urban temperature differences a string of T/RH data loggers located across Glasgow on a N-S transect. The measurement period was classified into three different atmospheric stability groups according to the modified Pasquill–Gifford–Turner (PGT) classification system. A consistent warming pattern was observed both between the farthest T/RH weather station and the group mean (intra-urban stations), although the UHI itself (in terms of temperature and comfort/discomfort levels) was not particularly affected by the choice of more stable conditions for analysis according to the PGT scheme. Urban planning implications of these findings are explored in the paper.

Classifying urban meteorological stations sites by 'local climate zones': Preliminary results for the city of Novi Sad (Serbia)

Conventional approach in the investigation of urban climate of Novi Sad has been done through simple urban-rural air temperature differences. These inter-urban air temperature differences showed how much is city warmer than its surroundings, so-called urban heat island (UHI) effect. Temperature differences exist inside the city as well. To get to know the intensity of these intra-urban temperature differences, installation of meteorological stations in different parts of the city or mobile measurements are needed. In 2012 started IPA HUSRB project made by Department of Climatology and Landscape Ecology (University of Szeged) and Faculty of Sciences (University of Novi Sad). The main goal of this project is the development and installation of wireless urban meteorological network (temperature and relative humidity sensors) in Szeged and Novi Sad. Before the deployment of sensors, necessary metadata about each potential urban meteorological station site needs to be collected. Field work, collected metadata and Stewart and Oke climate-based classification system from 2012 were used for defining the potential urban meteorological stations sites on the territory of the city of Novi Sad (Serbia) and its surroundings.

Urban heat islands and landscape heterogeneity: linking spatiotemporal variations in surface temperatures to land-cover and socioeconomic patterns

The urban heat island (UHI) phenomenon is a common environmental problem in urban landscapes which affects both climatic and ecological processes. Here we examined the diurnal and seasonal characteristics of the Surface UHI in relation to land-cover properties in the Phoenix metropolitan region, located in the northern Sonoran desert, Arizona, USA. Surface temperature patterns derived from the Advanced Spaceborne Thermal Emission and Reflection Radiometer for two day-night pairs of imagery from the summer (June) and the autumn (October) seasons were analyzed. Although the urban core was generally warmer than the rest of the area (especially at night), no consistent trends were found along the urbanization gradient. October daytime data showed that most of the urbanized area acted as a heat sink. Temperature patterns also revealed intra-urban temperature differences that were as large as, or even larger than, urban–rural differences. Regression analyses confirmed the important role of vegetation (daytime) and pavements (nighttime) in explaining spatio-temporal variation of surface temperatures. While these variables appear to be the main drivers of surface temperatures, their effects on surface temperatures are mediated considerably by humans as suggested by the high correlation between daytime temperatures and median family income. At night, however, the neighborhood socio-economic status was a much less controlling factor of surface temperatures. Finally, this study utilized geographically weighted regression which accounts for spatially varying relationships, and as such it is a more appropriate analytical framework for conducting research involving multiple spatial data layers with autocorrelated structures.

Vegetation as an urban climate control in the subtropical city of Gaborone, Botswana

AbstractThe influence of vegetation on the urban climate was studied in the subtropical city Gaborone, the rapidly expanding capital of Botswana with approximately 200 000 inhabitants. Temperature records from an urban and a rural station were analysed for the period 1985–96. In an attempt to explain possible seasonal change in vegetation, NOAA satellite normalized difference vegetation index imagery was analysed. The present urban influence was investigated with temperature loggers at selected urban and rural sites. In addition, mobile measurements revealed spatial patterns in temperature and humidity for different land uses.Seasonal patterns of urban–rural differences in minimum temperatures emerge during the period 1994–96, especially during the winter when the heat island effect is largest. It is shown that differences in urban and rural vegetation over the year partly explain this variation. Mobile measurements reveal a weak nocturnal heat island of 2–3 °C during clear and calm nights. There are intra‐urban temperature differences that are in the same range as the urban–rural relationship due to the role of vegetation. Evapotranspiration lowers the temperature, which was detected by high humidity in areas of lush vegetation. This becomes apparent at midday, when densely vegetated areas were up to 2 °C cooler than rural sites. An oasis effect, therefore, only exists on a highly local basis. In contrast, parts of the city with sparse vegetation are warmer than the countryside.There is an apparent opposed effect of rural and urban vegetation, whereby the former is hindering the temperature from falling and the latter is cooling the environment through evapotranspiration. This can be explained by the overwhelming amounts of imported water in the city promoting evaporative cooling. Copyright © 2004 Royal Meteorological Society