Towards a new methodology to determine nighttime Urban Heat Island

2021 ◽  
Author(s):  
Blanca Arellano ◽  
Josep Roca
Keyword(s):  
Urban Heat Island ◽  
Heat Waves ◽  
Surface Radiation ◽  
Urban Landscapes ◽  
Heat Island ◽  
Structural Problems ◽  
Thermal Data ◽  
Satellite Sensors ◽  
Urban Heat ◽  
Weather Stations

<p>The study of urban heat island (UHI) is of great importance in the context of climate change (CC). The literature on urban climate has highlighted the singular importance of night UHI phenomenon. It is during the night that the effects of UHI become most evident due to the low cooling capacity of urban construction materials and it is during nighttime that the accumulated heat and high temperatures can generate greater risks to health, leading to aggravate the negative impacts on people's health and comfort, especially in extreme events such as heat waves.</p><p>Traditional methods for obtaining nocturnal UHI have been directed either to extrapolation of data from weather stations. The lack of weather stations in urban landscapes makes it extremely difficult to obtain data to extrapolate and propose models at a detailed resolution scale.</p><p>The low spatial resolution of the air temperature information contrasts with the higher resolution of the thermal data of the land covers supplied by the satellite sensors. There is a high consensus that the temperature of the earth's surface (LST) plays a fundamental role in the generation of UHI, representing a determinant of surface radiation and energy exchange, as well as the control of the heat distribution between surface and atmosphere. However, the study of the nocturnal LST is still poorly developed due to structural problems related to the availability of detailed data on the LST at night. Most of the satellite sensors (Landsat, Aster, ...) allow to obtain daytime thermal images, but in a much more limited way nighttime thermal data. Only MODIS or Sentinel 3 provide abundant thermal night images, but the low resolution of these images (1 km / pixel) does not allow the construction of detailed models of the nocturnal UHI. For these reasons, estimating the nocturnal UHI remains a pending challenge.</p><p>This paper aims to develop a new methodology to determine nighttime LST using data from Landsat thermal bands and contrasting Landsat's very limited nighttime images with daytime ones. The contrast between the daytime and nighttime LST allows the construction of “cooling” models of the LST based on geographic characteristics and urban-spatial parameters, which could be extrapolated to different periods of time (during the same season).</p><p>However, the estimation of the LST from nighttime Landsat thermal bands is not a trivial question. The most used methodology to determine daytime LST is based on estimating the emissivity of the land from its degree of vegetation (NDVI threshold). But this method shows significant limitations at night. The NDVI overvalues vegetation when considering the canopy of trees. This overestimation may be correct during the day, when the shade of the trees limits the radiation incident on the ground. But it is critical at night.</p><p>For this reason, this paper seeks to develop a new methodology to estimate the degree of vegetation and soil moisture, and, based on it, determine the emissivity and, consequently, the nocturnal LST.</p><p>The case study is the Metropolitan Area of Barcelona (636 km<sup>2</sup>, 3.3 million inhabitants).</p>

Measuring night-time urban heat island. Still a pending issue

2020 ◽  
Author(s):  
Josep Roca ◽  
Blanca Arellano
Keyword(s):  
Urban Heat Island ◽  
Land Surface ◽  
Heat Waves ◽  
Heat Island ◽  
Night Time ◽  
Structural Problems ◽  
First Case ◽  
Urban Heat ◽  
Weather Stations ◽  
Land Covers

<p>The study of urban heat island (UHI) is of great relevance in the context of climate change (CC) and global warming. Cities accumulate heat in urban land covers as well as in built infrastructures, representing true islands of heat in relation to their rural environment, less urbanized. The literature on urban climate has highlighted the singular importance of night UHI phenomenon. It is during the night that the effects of UHI become more apparent, due to the low cooling capacity of urban construction materials and is during nighttime that temperatures can cause higher health risks, leading to the aggravation of negative impacts on people’s health and comfort in extreme events such as heat waves becoming more and more frequent and lasting longer. However, the study of nocturnal UHIs is still poorly developed, due to the structural problems regarding the availability of land surface and air temperature data for night time.</p><p>Traditional methods for obtaining nocturnal UHI have been directed either to extrapolation of data from weather stations, or obtaining air temperatures through urban transects. In the first case, the lack of weather stations in urban landscapes makes it extremely difficult to obtain data to extrapolate and propose models at a detailed resolution scale. In the second case, there is a manifest difficulty in obtaining data simultaneously and significantly representative of urban and rural zones. Another used methodology for measuring the nocturnal UHI is remote sensing from MODIS images, but the greatest limitation about this method is the low resolution, therefore it is clear the need for open source databases with better or higher resolution to quantify the night surface temperature.</p><p>This paper aims to develop a model for nocturnal UHI analysing several areas of Alta and Baja California as well as in the Mediterranean Coast, using data from the Landsat thermal bands (with an spatial resolution of 30 square meters per pixel) and contrasting Landsat's very limited nighttime images with daytime ones. The contrast allows the construction of “cooling” models of the LST based on geographical characteristics (longitude, latitude, distance to the sea, DTM, slope, orientation, etc.) and urban-spatial parameters (land uses and land covers), which are likely to be extrapolated to different time periods.</p>

scholarly journals Satellite Remote Sensing of Surface Urban Heat Islands: Progress, Challenges, and Perspectives

2018 ◽  
Vol 11 (1) ◽  
pp. 48 ◽  
Author(s):  
Decheng Zhou ◽  
Jingfeng Xiao ◽  
Stefania Bonafoni ◽  
Christian Berger ◽  
Kaveh Deilami ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Urban Heat Island ◽  
Land Surface ◽  
Time Of Day ◽  
Thematic Mapper ◽  
Urban Heat Islands ◽  
Heat Island ◽  
Annual Variations ◽  
Satellite Sensors ◽  
Urban Heat

The surface urban heat island (SUHI), which represents the difference of land surface temperature (LST) in urban relativity to neighboring non-urban surfaces, is usually measured using satellite LST data. Over the last few decades, advancements of remote sensing along with spatial science have considerably increased the number and quality of SUHI studies that form the major body of the urban heat island (UHI) literature. This paper provides a systematic review of satellite-based SUHI studies, from their origin in 1972 to the present. We find an exponentially increasing trend of SUHI research since 2005, with clear preferences for geographic areas, time of day, seasons, research foci, and platforms/sensors. The most frequently studied region and time period of research are China and summer daytime, respectively. Nearly two-thirds of the studies focus on the SUHI/LST variability at a local scale. The Landsat Thematic Mapper (TM)/Enhanced Thematic Mapper (ETM+)/Thermal Infrared Sensor (TIRS) and Terra/Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) are the two most commonly-used satellite sensors and account for about 78% of the total publications. We systematically reviewed the main satellite/sensors, methods, key findings, and challenges of the SUHI research. Previous studies confirm that the large spatial (local to global scales) and temporal (diurnal, seasonal, and inter-annual) variations of SUHI are contributed by a variety of factors such as impervious surface area, vegetation cover, landscape structure, albedo, and climate. However, applications of SUHI research are largely impeded by a series of data and methodological limitations. Lastly, we propose key potential directions and opportunities for future efforts. Besides improving the quality and quantity of LST data, more attention should be focused on understudied regions/cities, methods to examine SUHI intensity, inter-annual variability and long-term trends of SUHI, scaling issues of SUHI, the relationship between surface and subsurface UHIs, and the integration of remote sensing with field observations and numeric modeling.

scholarly journals Mitigating the Urban Heat Island Effect in Megacity Tehran

2014 ◽  
Vol 2014 ◽  
pp. 1-19 ◽  
Author(s):  
Sahar Sodoudi ◽  
Parisa Shahmohamadi ◽  
Ken Vollack ◽  
Ulrich Cubasch ◽  
A. I. Che-Ani
Keyword(s):  
Urban Heat Island ◽  
Rural Areas ◽  
Heat Waves ◽  
Mitigation Strategies ◽  
Cooling Effect ◽  
Heat Island ◽  
Microscale Model ◽  
Negative Effect ◽  
Urban Heat ◽  
Surrounding Areas

Cities demonstrate higher nocturnal temperatures than surrounding rural areas, which is called “urban heat island” (UHI) effect. Climate change projections also indicate increase in the frequency and intensity of heat waves, which will intensify the UHI effect. As megacity Tehran is affected by severe heatwaves in summer, this study investigates its UHI characteristics and suggests some feasible mitigation strategies in order to reduce the air temperature and save energy. Temperature monitoring in Tehran shows clear evidence of the occurrence of the UHI effect, with a peak in July, where the urban area is circa 6 K warmer than the surrounding areas. The mobile measurements show a park cool island of 6-7 K in 2 central parks, which is also confirmed by satellite images. The effectiveness of three UHI mitigation strategies high albedo material (HAM), greenery on the surface and on the roofs (VEG), and a combination of them (HYBRID) has been studied using simulation with the microscale model ENVI-met. All three strategies show higher cooling effect in the daytime. The average nocturnal cooling effect of VEG and HYBRID (0.92, 1.10 K) is much higher than HAM (0.16 K), although high-density trees show a negative effect on nocturnal cooling.

Can climate adaptation solutions fix the urban heat island? An assessment of the thermal conditions during heat waves in Vienna impacted by climate change and urban development scenarios for the mid-21st-century

2020 ◽  
Author(s):  
Paul Hamer ◽  
Heidelinde Trimmel ◽  
Philipp Weihs ◽  
Stéphanie Faroux ◽  
Herbert Formayer ◽  
...  
Keyword(s):  
Climate Change ◽  
Urban Heat Island ◽  
Heat Wave ◽  
Air Temperature ◽  
Urban Areas ◽  
Climate Adaptation ◽  
Heat Waves ◽  
Heat Island ◽  
Human Thermal Comfort ◽  
Urban Heat

<p>Climate change threatens to exacerbate existing problems in urban areas arising from the urban heat island. Furthermore, expansion of urban areas and rising urban populations will increase the numbers of people exposed to hazards in these vulnerable areas. We therefore urgently need study of these environments and in-depth assessment of potential climate adaptation measures.</p><p>We present a study of heat wave impacts across the urban landscape of Vienna for different future development pathways and for both present and future climatic conditions. We have created two different urban development scenarios that estimate potential urban sprawl and optimized development concerning future building construction in Vienna and have built a digital representation of each within the Town Energy Balance (TEB) urban surface model. In addition, we select two heat waves of similar frequency of return representative for present and future conditions (following the RCP8.5 scenario) of the mid 21<sup>st</sup> century and use the Weather Research and Forecasting Model (WRF) to simulate both heat wave events. We then couple the two representations urban Vienna in TEB with the WRF heat wave simulations to estimate air temperature, surface temperatures and human thermal comfort during the heat waves. We then identify and apply a set of adaptation measures within TEB to try to identify potential solutions to the problems associated with the urban heat island.</p><p>Global and regional climate change under the RCP8.5 scenario causes the future heat wave to be more severe showing an increase of daily maximum air temperature in Vienna by 7 K; the daily minimum air temperature will increase by 2-4 K. We find that changes caused by urban growth or densification mainly affect air temperature and human thermal comfort local to where new urbanisation takes place and does not occur significantly in the existing central districts.</p><p>Exploring adaptation solutions, we find that a combination of near zero-energy standards and increasing albedo of building materials on the city scale accomplishes a maximum reduction of urban canyon temperature of 0.9 K for the minima and 0.2 K for the maxima. Local scale changes of different adaption measures show that insulation of buildings alone increases the maximum wall surface temperatures by more than 10 K or the maximum mean radiant temperature (MRT) in the canyon by 5 K.  Therefore, additional adaptation to reduce MRT within the urban canyons like tree shade are needed to complement the proposed measures.</p><p>This study concludes that the rising air temperatures expected by climate change puts an unprecedented heat burden on Viennese inhabitants, which cannot easily be reduced by measures concerning buildings within the city itself. Additionally, measures such as planting trees to provide shade, regional water sensitive planning and global reduction of greenhouse gas emissions in order to reduce temperature extremes are required.</p><p>We are now actively seeking to apply this set of tools to a wider set of cases in order to try to find effective solutions to projected warming resulting from climate change in urban areas.</p>

scholarly journals Analysis of Urban Heat Island and Heat Waves Using Sentinel-3 Images: a Study of Andalusian Cities in Spain

2021 ◽  
Author(s):  
David Hidalgo García
Keyword(s):  
Solar Radiation ◽  
Urban Heat Island ◽  
Heat Wave ◽  
Land Surface ◽  
Heat Waves ◽  
Economic Cost ◽  
Heat Island ◽  
Multivariate Relationships ◽  
Urban Heat ◽  
Wave Conditions

Abstract At present, understanding the synergies between the Surface Urban Heat Island (SUHI) phenomenon and extreme climatic events entailing high mortality, i.e., heat waves, is a great challenge that must be faced to improve the quality of life in urban zones. The implementation of new mitigation and resilience measures in cities would serve to lessen the effects of heat waves and the economic cost they entail. In this research, the Land Surface Temperature (LST) and the SUHI were determined through Sentinel-3A and 3B images of the eight capitals of Andalusia (southern Spain) during the months of July and August of years 2019 and 2020. The objective was to determine possible synergies or interaction between the LST and SUHI, as well as between SUHI and heat waves, in a region classified as highly vulnerable to the effects of climate change. For each Andalusian city, the atmospheric variables of ambient temperature, solar radiation, wind speed and direction were obtained from stations of the Spanish State Meteorological Agency (AEMET); the data were quantified and classified both in periods of normal environmental conditions and during heat waves. By means of Data Panel statistical analysis, the multivariate relationships were derived, determining which ones statistically influence the SUHI during heat wave periods. The results indicate that the LST and the mean SUHI obtained are statistically interacted and intensify under heat wave conditions. The greatest increases in daytime temperatures were seen for Sentinel-3A in cities by the coast (LST = 3.90 °C, SUHI = 1.44 °C) and for Sentinel-3B in cities located inland (LST = 2.85 °C, SUHI = 0.52 °C). The existence of statistically significant positive relationships above 99% (p < 0.000) between the SUHI and solar radiation, and between the SUHI and the direction of the wind, intensified in periods of heat wave, could be verified. An increase in the urban area affected by the SUHI under heat wave conditions is reported. Graphical Abstract

scholarly journals A review of studies involving the effect of land cover and land use on the urban heat island phenomenon, assessed by means of the MUKLIMO model

Geografie ◽  
2019 ◽  
Vol 124 (1) ◽  
pp. 83-101 ◽  
Author(s):  
Ján Feranec ◽  
Monika Kopecká ◽  
Daniel Szatmári ◽  
Juraj Holec ◽  
Pavel Šťastný ◽  
...  
Keyword(s):  
Land Use ◽  
Land Cover ◽  
Urban Heat Island ◽  
Urban Areas ◽  
Rural Landscape ◽  
Urban Heat Islands ◽  
Urban Landscapes ◽  
Heat Island ◽  
Atmospheric Conditions ◽  
Urban Heat

The urban heat island phenomenon occurs in urban areas. It is characterized by increased temperature of both the air and ground surface, compared to the surrounding rural landscape, and is a typical feature of the urban climate. As this phenomenon may affect quality of life in the cities, a variety of scientific studies have been carried out. The article provides a review and evaluation of selected published studies devoted to the issue of the urban heat island, from the point of view of the application of land cover and land use data in the 3-dimensional microscale urban model. Part of the review brings into focus the MUKLIMO model, which computes the atmospheric conditions in urban landscapes and predicts thermal and other climatic characteristics. Evaluated studies confirmed the correlation between the land cover/land use classes and occurrence of the urban heat islands, i.e. a higher percentage of impermeable surfaces within the urban heat island causes more intensive thermal manifestation. The urban heat island effect diminishes when there are less impermeable surfaces and a greater representation of urban greenery in land cover/land use classes.

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