Dynamics Of Urban Heat Island Research Articles

Effect of COVID-19 Lockdown on Urban Heat Island Dynamics in Prague, Czechia

Urban heat islands (UHI) are a well-known phenomenon adversely affecting human health and urban environments. The worldwide COVID-19 lockdown in 2020 provided a unique opportunity to investigate the effects of decreased emission of air pollution and anthropogenic heat flux (AHF) on UHI. Although studies have suggested that reduced AHF during lockdown decreased atmospheric UHI (AUHI) and surface UHI (SUHI), these results contain inherent uncertainties due to unaccounted weather variability and urban-rural dynamics. Our study comprehensively analyzes the impact of the COVID-19 lockdown on AUHI and SUHI in Prague, Czechia. By selecting days with similar weather conditions, we examined changes in mean SUHI using MODIS satellite images and in AUHI based on air temperature from Prague weather stations for the Lockdown period during March–April 2020 versus a Reference period from March–April 2017–2019. Our results show that, in comparison to the Reference period, the Lockdown period was associated with a 15% (0.1 °C) reduction of SUHI in urbanized areas of Prague and a 0.7 °C decline in AUHI in the city center. Additionally, the observed decreases in satellite-based aerosol optical depth and nitrogen dioxide by 12% and 29%, respectively, support our hypothesis that the weakened UHI effects were linked to reduction in anthropogenic activities during the lockdown. Revealing the largest decrease of mean SUHI magnitude around the periphery of Prague, which has predominantly rural land cover, our study emphasizes the need to consider the effects of urban-rural dynamics when attributing changes in SUHI to AHF. Our findings provide additional insights into the role of reduced anthropogenic activities in UHI dynamics during the COVID-19 lockdown and offer policymakers a comprehensive understanding of how the complex interaction between urban and rural microclimate dynamics influences the SUHI phenomenon.

Urban Heat Island Dynamics in an Urban–Rural Domain with Variable Porosity: Numerical Methodology and Simulation

Heat transfer and fluid dynamics modeling in porous media is a widely explored topic in physics and applied mathematics, and it involves advanced numerical methods to address its non-linear nature. One interesting application has been the urban-heat-island (UHI) numerical simulation. The UHI is a negative consequence of the increasing urbanization in cities, which is defined as the presence of warm temperatures inside the urban canopy in contrast to the colder surroundings. Furthermore, an interesting phenomena occurs within a UHI context when the city transitions from a heat island to a cold island, matching the increases and decreases of solar radiation over the span of a day, as well as the decrease in the UHI intensity as a result of wind action. The numerical study in this paper had, as its main goal, to reproduce this phenomenon. Therefore, the key elements proposed in this work were the following: A 2D horizontal urban–rural domain that had a variable porosity with a Gaussian distribution centered in the city center. A non-stationary Darcy–Forchheimer–Brinkman model to simulate the flow in porous media, combined with an air–soil heat transport model linked by a balancing equation for the surface energy that includes the evapotranspiration of plants. In regards to the numerical resolution of the model, a classical numerical methodology based on the finite elements of Lagrange P1 type combined with explicit and implicit time-marching schemes have been effective for high-quality numerical simulations. Several numerical tests were performed on a domain inspired by the metropolitan region of Guadalajara (Mexico), in which not only the temperature inversion was reproduced but also the simulation of the UHI transition by strong wind gusts.

Dynamics of Urban Heat Island and Anthropogenic Emissions in Bekasi before and during COVID-19 Pandemic using Landsat 8 and Sentinel-5P

The rise in temperature in urban areas resulting in UHI formation is thought to be significantly driven by anthropogenic emissions due to human activities. During the COVID-19 pandemic, the Indonesian government issued the Large-Scale Social Restrictions (PSBB) and Community Activities Restrictions Enforcement (PPKM) policy. Bekasi Regency is part of the Jabodetabek megapolitan that applied strict PSBB and PPKM treatment during the pandemic. The decreasing industrial activity and traffic volume are expected to reduce air pollutants and thermal radiation. The research method uses processed satellite imagery from Sentinel 5P to get anthropogenic emissions concentrations (NO2 and SO2) and Landsat 8 to get land surface temperature (LST). The results showed that Bekasi had a slight decrease in the concentration of anthropogenic emissions during COVID-19 pandemic 2020, then increased during COVID-19 pandemic 2021. The areas affected by urban heat islands increased steadily during the COVID-19 pandemic. Therefore, when the concentration of anthropogenic emissions rises, the UHI ascends.

Characterizing Temporal Dynamics of Urban Heat Island in a Rapidly Expanding City: A 39 Years Study in Zhengzhou, China

Extreme heat wave weather phenomena have erupted worldwide in recent years. The urban heat island (UHI) effect has exacerbated urban heat waves with serious consequences for urban energy and residents’ health. Therefore, a better understanding of the dynamics of the UHI effect and the influencing factors is needed in the context of carbon neutrality and global warming. This study used long-term observation and statistical data to investigate the urban heat island intensity (UHII) over the past 39 years (1981–2019) and to analyze the temporal changes of the UHI effect and the relationship between the UHI effect and indicators of rapid urbanization in Zhengzhou, China. The results showed that Zhengzhou is warming 2.2-times faster than the global land warming trend of about +0.9 °C from 1981 to 2019. There is a clear phase characteristic of the heat island effect in Zhengzhou, and it offers a rapid upward trend after 2000 and a positive correlation with the urbanization process; it was found that the social and economic conditions of urban expansion in Zhengzhou have a significant relationship with UHII. We also found that the denser the urban built-up area, the more obvious the heat island effect. Compared with other countries, the influence of national policies on urban development is an indirect factor influencing the change of UHI specifically for Chinese cities. This research could provide a reference for understanding the temporal dynamics of UHI in an expanding large city for sustainable urban planning and mitigating urban warming and environmental problems.

Urban heat island dynamics in response to land use land cover change: a case of Jimma city, southwestern Ethiopia

Urban heat island dynamics in response to land use land cover change: a case of Jimma city, southwestern Ethiopia

Urban Heat Island Dynamics in Response to Land-Use/Land-Cover Change in the Coastal City of Mumbai

Urban Heat Island Dynamics in Response to Land-Use/Land-Cover Change in the Coastal City of Mumbai

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.

An Eleven Years Analysis of the Seasonal Dynamics of Urban Heat Island (UHI) Intensity (2004-2014)

An Eleven Years Analysis of the Seasonal Dynamics of Urban Heat Island (UHI) Intensity (2004-2014)

Temporal dynamics of urban heat island correlated with the socio-economic development over the past half-century in Seoul, Korea

Urban heat island (UHI), an iconic consequence of anthropogenic activities and climate condition, affects air pollution, energy use, and health. Therefore, better understanding of the temporal dynamics of UHI is required for sustainable urban planning to mitigate air pollution under a changing climate. Here, we present the evolution of UHI intensity (UHIi) and its controlling factors in the Seoul metropolitan area, Korea, over the last 56 years (1962–2017), which has experienced unique compressed economic growth and urban transformation under monsoon climate. The analysis demonstrated an inverted U-shape long-term variation of UHIi with the progress of urban transformation and economic climate which has not been reported in Asian cities before. Meanwhile, short-term variations in UHIi are related to both diurnal temperature range and duration after rainfall event unlike previous studies, and the UHIi was exacerbated by heat waves. Our findings suggest that the UHIi will exhibit different temporal dynamics with future changes in the monsoon climate, and heat waves in the urban area will be reinforced if current rapid urbanization continues without a shift toward sustainable and equitable development. Asian cities that are likely to face the similar urbanization trajectory and the implications are that urban (re)development strategy considers changes in rainfall magnitude and timing due to monsoon system variation under changing climate and plans to mitigate synergy between heat wave and UHI in this area.

Area Delineation and Spatial-Temporal Dynamics of Urban Heat Island in Lanzhou City, China Using Remote Sensing Imagery

One of the key impacts of rapid urbanization on the environment is the effect of urban heat island (UHI). By using the Landsat TM/ETM+ thermal infrared remote sensing data of 1993, 2001 and 2011 to retrieve the land surface temperature (LST) of Lanzhou City, and by adopting object-oriented fractal net evolution approach (FNEA) to make image segmentation of the LST, the UHI elements were extracted. The G* index spatial aggregation analysis was made to calculate the urban heat island ratio index (URI), and the landscape metrics were used to quantify the changes of the spatial pattern of the UHI from the aspects of quantity, shape and structure. The impervious surface distribution and vegetation coverage were extracted by a constrained linear spectral mixture model to explore the relationships of the impervious surface distribution and vegetation coverage with the UHI. The information of urban built-up area was extracted by using UBI (NDBI-NDVI) index, and the effects of urban expansion on city thermal environment were quantitatively analyzed, with the URI and the LST grade maps built. In recent 20 years, the UHI effect in Lanzhou City was strengthened, with the URI increased by 1.4 times. The urban expansion had a spatiotemporal consistency with the UHI expansion. The patch number and density of the UHI landscape were increased, the patch shape and the whole landscape tended to be complex, the landscape became more fragmented, and the landscape connectivity was decreased. The heat island strength had a negative linear correlation with the urban vegetation coverage, and a positive logarithmic correlation with the urban impervious surface coverage.

Volcanic Ash and the Respiratory Immune System - Possible Mechanisms behind Reported Infections

Ash plumes erupting from volcanoes can cause a range of health effects following exposure either to the initial emissions or to deposited material that becomes resuspended days, months, or years later. Researchers from the United States, Iceland, and Australia now report in EHP evidence that exposure to volcanic ash may both foster bacterial growth in the respiratory system and weaken the ability of the immune system to limit that growth, possibly contributing to respiratory infections that have been documented in relation to past eruptions.1 Each year eruptions occur at about 50–70 above-sea locations; eruptions have been documented for about 550 volcanoes in all, and roughly 1,300 have been active at some point in the past 10,000 years.2 Some of this activity generates ash plumes that affect potentially millions of people. Volcanic ash can contain significant quantities of respirable particles of rock, minerals, and volcanic glass, and eruptions also emit hazardous gases such as sulfur dioxide, hydrogen sulfide, hydrochloric acid, and hydrofluoric acid.3 The 20 March 2010 eruption of the Icelandic volcano Eyjafjallajokull (pronounced, roughly, AY-yah-FYET-lah-YOH-kuhl), another larger eruption on 14 April 2010, and ongoing volcanic activity through late May 2011 ejected numerous major ash plumes that spread far and wide. For the current study, the researchers primarily used one sample of this ash that was collected on the ground 15 April 2010 at a location 58 km from the volcano. The ash was composed of a complex mixture of aluminosilicate volcanic glass and minerals including iron, titanium, manganese, zinc, strontium, and barium. The researchers used a ubiquitous and potent opportunistic human bacterium, Pseudomonas aeruginosa,4 to test for possible interaction between ash and this sample infectious agent in primary human airway epithelial cells, primary rat alveolar epithelial cells, and primary human and rat alveolar macrophages. Iron-rich ash from the Eyjafjallajokull eruption spread over thousands of square kilometers. A high-power scanning electron microscopy image shows a smooth-surfaced alveolar macrophage in the process of engulfing (“phagocytizing”) ash particles collected by the authors. The authors conclude that reports of increased respiratory infections following eruptions may reflect an ability of volcanic ash to spur the growth of bacteria as well as interfere with innate immunity. They found a statistically significant increase in growth of the cultured bacteria after ash exposure, possibly due in part to bioavailable iron in the ash. They treated the cultured bacteria with antimicrobial peptides, some with and some without ash included. Bacterial growth was inhibited by the peptides as expected, but less so when ash was included. There was some evidence that ash exposure might impede functions of macrophages including autophagy, bacterial killing ability, and inflammatory responses, but those results didn’t reach statistical significance. However, unlike particles found in cigarette smoke and diesel exhaust, the ash did not kill human airway epithelial cells or rat alveolar epithelial cells nor did it disrupt epithelial cell barrier integrity.1 The study results are “very significant, given there are no current risk assessments or therapeutic interventions in place for avoiding potential respiratory infections following exposure to ash, especially for sensitive groups such as asthmatics, infants, and the elderly,” says Kelly BeruBe, director of the Lung and Particle Research Group at Cardiff University in Wales. But BeruBe cautions that numerous limitations of the study make it premature to apply the findings to real-world human exposures. For instance, the ash sample tested was a mixture of coarse and fine particles collected on the ground rather than from the air at a height typical of inhalation. She says this makes it impossible to determine if the effects were caused by the fine particles in this mixture (a size that has been identified in a wealth of studies as especially harmful). In addition, the cultured human cells tested came from only two people and thus aren’t representative of many important variables such as age, health status, risk behaviors, and area of geographic residence. The study also did not address any possible confounding effects of coexposure to toxic gases emitted during eruptions. Volcanic ash can vary substantially depending on factors such as the geochemistry of the individual volcano, the phase of and distance from the eruption, and the degree of posteruption weathering the ash has undergone. Even for the one sample in this study, the published information was too limited to allow accurate analysis of all its mineralogical characteristics, making the study results “problematic for comparisons with other volcano ash,” says Tim Jones, a senior lecturer in environmental geology at Cardiff University. Nonetheless, he says, “This is certainly a step forward in our understanding of the bioreactivity of volcanic ash.”

How do variations in Urban Heat Islands in space and time influence household water use? The case of Phoenix, Arizona

This paper explores how urbanization, through its role in the evolution of Urban Heat Island (UHI), affects residential water consumption. Using longitudinal data and drawing on a mesoscale atmospheric model, we examine how variations in surface temperature at the census tract level have affected water use in single family residences in Phoenix, Arizona. Results show that each Fahrenheit rise in nighttime temperature increases water consumption by 1.4%. This temperature effect is found to vary significantly with lot size and pool size. The study provides insights into the links between urban form and water use, through the dynamics of UHI.

Spatial and Temporal Dynamics of Urban Heat Island and Their Relationship with Land Cover Changes in Urbanization Process: A Case Study in Suzhou, China

One of the significant environmental consequences of urbanization is the urban heat island (UHI). In this paper, Landsat TM images of 1986 and 2004 were utilized to study the spatial and temporal variations of heat island and their relationships with land cover changes in Suzhou, a Chinese city which experienced rapid urbanization in past decades. Land cover classifications were derived to quantify urban expansions and brightness temperatures were computed from the TM thermal data to express the urban thermal environment. The spatial distributions of surface temperature indicated that heat islands had been largely broadened and showed good agreements with urban expansion. Temperature statistics of main land cover types showed that built-up and bare land had higher surface temperatures than natural land covers, implying the warming effect caused by the urbanization with natural landscape being replaced by urban areas. In addition, the spatial detail distributions of surface temperature were compared with the distribution of land cover by means of GIS buffer analysis. Results show remarkable show good correspondence between heat island variations with urban area expansions.

Urban heat island dynamics in Montreal and Vancouver

Automobile traverses were used to gather time-series air temperature data in Montreal, Quebec and Vancouver, British Columbia on selected nights. Using urban-rural cooling rates, the roles of urban and rural surfaces in the growth and decay of the urban heat island were investigated. The heat island grew most rapidly following sunset because of much stronger rural cooling. The maximum heat island occurred 3–5 h after sunset in both cities, and in both summer and winter. Rural cooling followed Brunt's formula, but the urban area showed a linear drop in temperature with time. Hence it was possible to assign a rural thermal admittance, but not an urban one. The results suggest that nocturnal energy exchange in the city is complex.