Features of the heat island in seoul and its surrounding cities

This study describes the characteristics of the heat island in Seoul, Korea and its surrounding cities based on automobile observations from June to August in 1982. The highest temperature anomaly region (e.g. urban) had the smallest standard deviation, while the lowest temperature anomaly areas (e.g. suburban, rural) had the largest standard deviations. Wind speed was the main limiting factor of the heat island intensity. The critical wind speed, which destroys the heat island, increased with city size and it was found 10 be 11.1 m s⁻¹ in Seoul. Statistical analyses revealed a close relationship between urban indices, such as surface impermeability and population and the heat island intensity. The maximum heat island intensity increased with urban population, however, and the slope of the regression line increased sharply from 1.46 to 3.43 at the point of around 300,000 inhabitants. There was a similar relationship between population and impermeable surface coverage. A relationship between maximum heat island intensity and ratio (%) of impermeable surface was clearly observed. Therefore, this points to a strong interrelationship between the heat island intensity, population, and impermeable surface coverage.     

On relationships between heat island and sky view factor in the cities of Tama River basin,Japan

This study aims at firstly identifying heat island phenomena, secondly relating heat island intensity to city size, and thirdly providing basic urban climatic information to city planners or ordinary citizens. Horizontal distributions of dry- and wet-bulb temperature were measured seasonally in small to medium sized cities by mobile observers. Also, at a fixed station, wind speed and wind direction in addition to temperature were observed.The cities selected for this were Tachikawa, Fuchu, Fussa, Higashimurayama and Akikawa, which are suburban cities in the W part of Tokyo. This area is part of the middle basin of Tama River. Observations were made both during the day and at night in winter (February and December), spring (March and May), summer (July and August) and autumn (October and November) over a period of maximum duration of 1.5 h. In all cities heat islands were observed to develop to some extent. Their intensities were largely dependent on weather conditions.Cities in Japan have been growing rapidly and randomly, and merging into neighbouring small cities or towns. This expansion is called sprawl. Due to these factors it is very difficult to determine a good indicator of city sizes, i.e. population or DID (Densely Inhabited District) population does not represent the effect of city size on heat island intensity. Sky view factors were determined using a fish-eye lens and a calculation chart.We therefore examined central urban area and sky view factor as a cause factor for heat islands. It is concluded that sky view factor is a very useful indicator of the effect of urbanization on heat island intensity.     

Influences of the city of Bucharest on weather and climate parameters

Estimates of the urban heat island are presented based upon ground level air temperature measurement in a few representative points in Bucharest (May–December 1994). The intensity of the effect is analysed versus synoptic mesoscale patterns. Other effects of the urban area on some atmospheric parameters, particularly on cloud systems and precipitation, are presented, too, using radar images.     

Complexity of the relationship between 2D/3D urban morphology and the land surface temperature: a multiscale perspective

Environmental Science and Pollution Research - Urban morphology is a crucial contributor to urban heat island (UHI) effects. However, few studies have explored the complex effect of 2D/3D urban...     

The effect of atmospheric thermal conditions and urban thermal pollution on all-cause and cardiovascular mortality in Bangladesh

This study assessed the effect of temperature and thermal atmospheric conditions on all-cause and cardiovascular mortality in Bangladesh. In particular, differences in the response to elevated temperatures between urban and rural areas were investigated. Generalized additive models (GAMs) for daily death counts, adjusted for trend, season, day of the month and age were separately fitted for urban and rural areas. Breakpoint models were applied for determining the increase in mortality above and below a threshold (equivalent) temperature. Generally, a 'V'-shaped (equivalent) temperature-mortality curve with increasing mortality at low and high temperatures was observed. Particularly, urban areas suffered from heat-related mortality with a steep increase above a specific threshold. This adverse heat effect may well increase with ongoing urbanization and the intensification of the urban heat island due to the densification of building structures. Moreover, rising temperatures due to climate change could aggravate thermal stress.     

Numerical simulation of the urban boundary layer over the complex terrain of Hong Kong

Due to the complexity of the underlying surface, urban boundary layers may exhibit very different wind-temperature field structures compared with rural areas. In this study, an urban boundary layer model with a resolution of 500 m is applied to Hong Kong, a place characterized by complex topography with high mountains and dense urban developments. Five surface land use types are considered; grass and shrub land, trees, water, old urban areas and new town developments. The urban boundary layer model is embedded into the National Center for Atmospheric Research (NCAR) Mesoscale Model, version 5 (MM5). The initial and boundary conditions are obtained from the National Centers for Environmental Prediction (NCEP)/NCAR reanalysis dataset. The modeling approach therefore takes into account both the mesoscale background field and the urban underlying surface. The model is applied to the simulation of a pollution episode in Hong Kong. Results show good agreement with meteorological data for the surface winds and temperature. The model successfully simulates the urban heat island and the occurrence of a sea–land breeze circulation, and their impact on air pollutant transport and dispersion.     

Water transformation in the media of biofilters controlled by Rhodococcus fascians in treating an ethyl acetate-contaminated airstream

Biofilters do not provide much water for bacteria to grow. To use them efficiently and properly, it is essential to understand the kinetics of water transformation and to control moisture levels. This study aims to clarify whether the metabolism of microorganisms will improve the water-holding capacity of media or will intensify drying. This experiment was conducted in duplicate, that is, both with and without bacterial inoculation. Both the constant water content mode and the declining water content mode show that microbial growth in a log phase will enhance drying. In contrast, the bacteria growing in a logarithmic decline phase will improve water-holding capacity. Basically, water evaporation can result from the latent heat obtained from microbial respiration or from the physical temperature difference between the unsaturated air and the wet media. Two ways that biofilters can gain water are from water incorporated into bacteria cells and from water obtained from the oxidation of volatile organic compounds (VOCs).     

Water Transformation in the Media of Biofilters Controlled by Rhodococcus fascians in Treating an Ethyl Acetate-Contaminated Airstream

Abstract

Biofilters do not provide much water for bacteria to grow. To use them efficiently and properly, it is essential to understand the kinetics of water transformation and to control moisture levels. This study aims to clarify whether the metabolism of microorganisms will improve the water-holding capacity of media or will intensify drying. This experiment was conducted in duplicate, that is, both with and without bacterial inoculation. Both the constant water content mode and the declining water content mode show that microbial growth in a log phase will enhance drying. In contrast, the bacteria growing in a logarithmic decline phase will improve water-holding capacity. Basically, water evaporation can result from the latent heat obtained from microbial respiration or from the physical temperature difference between the unsaturated air and the wet media. Two ways that biofilters can gain water are from water incorporated into bacteria cells and from water obtained from the oxidation of volatile organic compounds (VOCs).     

An urban bias in air temperature fluctuations at the Klementinum,Prague, The Czech Republic

The intensification of an urban heat island, and its influence on the seasonal and annual air temperature measurements of the Prague-Klementinum station, is studied through a comparison with rural stations. Urban warming in the period from 1922 to 1995 was most conspicuous in winter and in spring (0.06°C 10 yr⁻¹), and the smallest and least significant in summer (0.01°C 10 yr⁻¹). Since the 1960s, a stagnation in the development of the urban heat island has appeared. The degree of urban warming prior to 1922 can only be roughly determined because of the lack of a suitable set of homogeneous reference stations. The results of this study are compared with other studies analogous in character.     

The energy balance of central Mexico City during the dry season

The first measurements of the energy balance fluxes of a dry, densely built-up, central city site are presented. Direct observation of the net radiation, sensible and latent heat flux densities above roof-top in the old city district of Mexico City allow the heat storage flux density to be found by residual. The most important finding is that during daytime, when evaporation is very small (<4% of net radiation), and therefore sensible heat uses dominate (Bowen ratio >8), the uptake of heat by the buildings and substrate is so large (58%) that convective heating of the atmosphere is reduced to a smaller role than expected (38%). The nocturnal release of heat from storage is equal to or larger than the net radiation and sufficient to maintain an upward convective heat flux throughout most nights. It is important to see if this pattern is repeated at other central city, or dry urban sites, or whether it is only found in districts dominated by massive stone structures. These findings have implications for the height of the urban mixing layer and the magnitude of the urban heat island.     

Comparison between the atmospheric boundary layer in Paris and its rural suburbs during the ECLAP experiment

The ECLAP experiment has been performed during the winter of 1995 in order to study the influence of the urban area of Paris on the vertical structure and diurnal evolution of the atmospheric boundary layer, in situations favourable to intense urban heat island and pollution increase. One urban site and one rural site have been instrumented with sodars, lidars and surface measurements. Additional radiosondes, 100 m masts and Eiffel Tower data were also collected. This paper gives a general overview of this experiment, and presents results of the analysis of four selected days, characterized by various wind directions and temperature inversion strengths. This analysis, which consists in a comparison between data obtained in the two sites, has been focused on three parameters of importance to the ABL dynamics: the standard deviation of vertical velocity, the surface sensible heat flux, and the boundary layer height. The vertical component of turbulence is shown to be enhanced by the urban area, the amplitude of this effect strongly depending on the meteorological situation. The sensible heat flux in Paris is generally found larger than in the rural suburbs. The most frequent differences range from 25–65 W m^-2, corresponding to relative differences of 20–60%. The difference of unstable boundary layer height between both sites are most of the time less than 100 m. However, sodar and temperature data show that the urban influence is enhanced during night-time and transitions between stable and unstable regimes.     

Impact of anthropogenic heat on urban climate in Tokyo

This study quantifies the contribution through energy consumption, to the heat island phenomena and discussed how reductions in energy consumption could mitigate impacts on the urban thermal environment. Very detailed maps of anthropogenic heat in Tokyo were drawn with data from energy statistics and a very detailed digital geographic land use data set including the number of stories of building at each grid point. Animated computer graphics of the annual and diurnal variability in Tokyo's anthropogenic heat were also prepared with the same data sources. These outputs characterize scenarios of anthropogenic heat emission and can be applied to a numerical simulation model of the local climate. The anthropogenic heat flux in central Tokyo exceeded 400 W m⁻² in daytime, and the maximum value was 1590 W m⁻² in winter. The hot water supply in offices and hotels contributed 51% of this 1590 W m⁻². The anthropogenic heat flux from the household sector in the suburbs reached about 30 W m⁻² at night. Numerical simulations of urban climate in Tokyo were performed by referring to these maps. A heat island appeared evident in winter because of weakness of the sea breeze from Tokyo Bay. At 8 p.m., several peaks of high-temperature appeared, around Otemachi, Shinjuku and Ikebukuro; the areas with the largest anthropogenic heat fluxes. In summer the shortwave radiation was strong and the influence of anthropogenic heat was relatively small. In winter, on the other hand, the shortwave radiation was weak and the influence of anthropogenic heat was relatively large. The effects of reducing energy consumption, by 50% for hot water supply and 100% for space cooling, on near surface air temperature would be at most −0.5°C.     

Tracer Study In an Urban Valley

Results of a series of nighttime tracer experiments conducted during the Autumn of 1966 in the industrialized valley of Johnstown, Pa., are discussed. Quite atypical meteorology and dispersion occur within a classical drainage flow framework. An urban heat island effect is observed creating uniform temperature and wind structures within a layer of air flowing through the valley. Dispersion in the valley at night is comparable to that of neutral conditions over open country.     

Is the Water Footprint an Appropriate Tool for Forestry and Forest Products: The Fennoscandian Case

The water footprint by the Water Footprint Network (WF) is an ambitious tool for measuring human appropriation and promoting sustainable use of fresh water. Using recent case studies and examples from water-abundant Fennoscandia, we consider whether it is an appropriate tool for evaluating the water use of forestry and forest-based products. We show that aggregating catchment level water consumption over a product life cycle does not consider fresh water as a renewable resource and is inconsistent with the principles of the hydrologic cycle. Currently, the WF assumes that all evapotranspiration (ET) from forests is a human appropriation of water although ET from managed forests in Fennoscandia is indistinguishable from that of unmanaged forests. We suggest that ET should not be included in the water footprint of rain-fed forestry and forest-based products. Tools for sustainable water management should always contextualize water use and water impacts with local water availability and environmental sensitivity.     

Suppression of precipitation by dust particles originated in the Tibetan Plateau

Dust aerosols play an important role in modulating the hydrologic cycle. The Tibetan Plateau (TP) is little polluted by human activities as an ideal site to study the effect of dust aerosol on precipitation. In this study, observational data of dust storms and precipitation in the TP and its vicinities as well as CALIPSO satellite data were used to analyze the distributions and vertical structure of dust storms on the plateau. The results showed that dust storms occur with high frequency and raise dust particles into the troposphere from ground level to a height of 5–9 km to modulate the hydrologic cycle in the TP. There are significant negative correlations between dust aerosol and precipitation in the dust source regions during the period of both 40 and 200 years. It is found that the role of precipitation in suppressing dust storms could be unimportant, while dust aerosol may play an important role in suppressing precipitation in the hinterland of the TP. Our study provides a potential approach to better understand the climate changes in the TP.     

Tracer Study In an Urban Valley

Results of a series of nighttime tracer experiments conducted during the Autumn of 1966 in the industrialized valley of Johnstown, Pa., are discussed. Quite atypical meteorology and dispersion occur within a classical drainage flow framework. An urban heat island effect is observed creating uniform temperature and wind structures within a layer of air flowing through the valley. Dispersion in the valley at night is comparable to that of neutral conditions over open country.     

Positive effects of vegetation: urban heat island and green roofs

This paper attempts to evaluate the positive effects of vegetation with a multi-scale approach: an urban and a building scale.Monitoring the urban heat island in four areas of New York City, we have found an average of 2 °C difference of temperatures between the most and the least vegetated areas, ascribable to the substitution of vegetation with man-made building materials.At micro-scale, we have assessed the effect of surface albedo on climate through the use of a climatological model. Then, using the CO₂ equivalents as indicators of the impact on climate, we have compared the surface albedo, and the construction, replacement and use phase of a black, a white and a green roof. By our analyses, we found that both the white and the green roofs are less impactive than the black one; with the thermal resistance, the biological activity of plants and the surface albedo playing a crucial role.     

Integrated chemical species analysis with source-receptor modeling results to characterize the effects of terrain and monsoon on ambient aerosols in a basin

This study integrated estimated oxidation ratio of sulfur (SOR) and oxidation ratio of nitrogen (NOR) with source-receptor modeling results to identify the effects of terrain and monsoons on ambient aerosols in an urban area (north basin) and a rural area (south basin) of the Taichung Basin. The estimated results indicate that the conversion of sulfur mainly occurs in fine particles (PM_2.5), whereas the conversion of nitrogen occurs in approximately equal quantities of PM_2.5 and coarse particles (PM_2.5–10). The results show a direct relationship for PM_2.5 between the modeling results with SOR and NOR. The high PM_2.5 SOR, NOR, and secondary aerosol values all occurred in the upwind area during both monsoons; this shows that the photochemical reaction and the terrain effect on the pollutant transmission were significant in the basin. Additionally, the urban heat island effect on the urban area and the valley effect on the rural area were significant. The results show that secondary aerosol in PM_2.5–10 contributed approximately 10 % during both monsoons, and the difference in the contribution from secondary aerosol between both areas was small. Vehicle exhaust emissions and wind-borne dust were two crucial PM_2.5–10 contributors during both monsoons; their average contributions in both areas were higher than 34 and 32 %, respectively.     

Carbon savings resulting from the cooling effect of green areas: a case study in Beijing

Green areas cool the climate of a city, reduce the energy consumption caused by the urban heat island (UHI) effect, and bring along carbon savings. However, the calculation of carbon savings due to the cooling effect of green areas is still not well understood. We have used a Landsat Enhanced Thematic Mapper Plus (ETM+) image of Beijing, to identify the cooled areas, compute the possible energy used to maintain the temperature differences between cooled areas and their surrounding heated areas, and calculate the carbon savings owing to the avoidance of energy use. Results show that a total amount of 14315.37 tons carbon savings was achieved in the study area and the amount was related to the biomass, the size and the shape of green areas. These results demonstrate the importance of carbon savings resulting from green areas' cooling effect.