Urbanization is known to cause significant changes to the properties of local climate. The Urban Heat Island (UHI) has been shown to add an additional burden to the impacts of global warming, impose risks on human health, and indirectly worsen air and water qualities. Studies have shown that urban areas, compared to rural areas with less artificial buildup, experience higher local temperatures as a result of UHI. Hong Kong is one of the most densely populated cities in the world with a high proportion of her population residing in urbanized areas. The hot and humid sub-tropical monsoon climate echoed with densely packed high-rise buildings and a high traffic volume can give rise to severe local thermal discomfort. To fully characterize the spatial and temporal aspects of UHI within Hong Kong’s urban areas, this study deployed 58 small, durable and low-cost logging sensors to measure road-side temperature/humidity measurements at 15-minute time intervals. The data collection was conducted over 17 consecutive days in the summer (September) and repeated in the winter (January) at two typical urban locations: Mong Kok and Causeway Bay. By employing the geographic information system (GIS) and global positioning system (GPS) software, the sampled data were mapped against urban structures and land uses to investigate the urban microclimate and the role of various environmental factors at the sampling locations. Official meteorological conditions for the duration of study were obtained from the Hong Kong Observatory to validate the sensors and to explore microclimate variations by comparing official (urban and rural monitoring stations) and sampled readings. Temporal variations of urban temperature were examined for daily, weekly and seasonal differences. Spatial and temporal variations were examined using spatial interpolation and hotspot analysis, as well as in a 3D representation with building models for better visualization. This empirical study establishes the methodological feasibility and reliability of employing small and inexpensive logging sensors for widespread deployment in places with hot and humid subtropical climates. The validation outcome indicated that road-side and control measurements were strongly correlated (r>0.81) and their average difference was well within the ±1 C measurement accuracy claimed by the manufacturer. Significant microclimate variations within the urban area were observed and characterized by five environmental settings: major road, secondary road, public activity area, green park and tunnel. Temporal variations of UHI were evident for all time scales, with the daily highest UHI at around midnight and daily lowest at around noon to early afternoon which also exhibited urban cool island (UCI) effects. A UHI Threat Rating was introduced for better understanding of microclimate variations and easier appreciation of hotspots. A 3D-GIS building model enhanced spatial-temporal analysis of UHI over a near “real” and 3D environment. The study and its methodology set a sound foundation and provide essential framework for future studies on microclimate variation and UHI effects. Given that modern cities have mixed land uses and are increasingly vertical, this micro-level study helps address local issues on human comfort and brings in the broader picture of environmental health in an urban setting. / published_or_final_version / Geography / Doctoral / Doctor of Philosophy

The urban heat island effect is considered one of the main causes of global warming and is contributing to increasing temperatures in the urban United States. This phenomenon enhances the intensity of summer heat waves and the risk to public health due to increased exposure to extreme thermal conditions. Characteristics of spatial development patterns can significantly affect urban temperature because they are related to the arrangement of development and land surface materials, which are crucial elements needed to determine land surface temperature. While previous studies revealed that the effect of the urban heat island varies depending on different land use types and surface characteristics, few have considered the overall development patterns of urban form. I address this under-studied aspect of heat hazards by analyzing the relationship between spatial development pattern and urban heat island effect across a sample of 353 metropolitan regions of the U.S. Specifically, I employ a series of landscape metrics to measure urban development patterns using a national land cover dataset from the U.S. Geological Survey. Linear regression models are used to statistically isolate the effect of different spatial development patterns on increasing the urban heat island effect while controlling for multiple contextual variables including built-environment, environmental, and demographic characteristics. The result of this study showed that the daytime mean surface urban heat island effect (4.04˚F) is higher than that of nighttime (2.41˚F). Ecological context (i.e. Ecoregions) has proved to be a statistically significant modulator that helps to explain the spatial distribution of the urban heat island effect. Regarding the main research question of this study, the results indicate that specific categories of urban development pattern including density, continuity, and clustering are statistically associated with increasing the urban heat island effect. This initial evidence suggests that the overall development patterns are an important issue to consider when mitigating the adverse impacts related to the urban heat island effect. In addition, when contextual heat contributors are held constant, the intensity of the urban heat island effect can differ depending on the configuration of development in urban areas. This study can be used as a starting point for a comprehensive approach to both spatial land development and hazard-resistant planning by providing alternative ways of measuring and modeling spatial development patterns.

Bibliography: p. 133-144. / x, 170 p. : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis investigates the impact on residential energy use for climate control or urban design variables, such as building density, spacing and orientation. Energy use for heating/cooling is predicted in a range of urban configurations that are compatible with the following objectives: wind shelter and solar access in winter and urban ventilation and shading in summer. / Thesis (Ph.D.)--University of Adelaide, Dept. of Architecture, 1997?

abstract: Metropolitan Phoenix, Arizona, is one of the most rapidly urbanizing areas in the U.S., which has resulted in an urban heat island (UHI) of substantial size and intensity. Several detrimental biophysical and social impacts arising from the large UHI has posed, and continues to pose, a challenge to stakeholders actively engaging in discussion and policy formulation for a sustainable desert city. There is a need to mitigate some of its detrimental effects through sustainable methods, such as through the application of low-water, desert-adapted low-water use trees within residential yards (i.e. urban xeriscaping). This has the potential to sustainably reduce urban temperatures and outdoor thermal discomfort in Phoenix, but evaluating its effectiveness has not been widely researched in this city or elsewhere. Hence, this dissertation first evaluated peer-reviewed literature on UHI research within metropolitan Phoenix and discerned several major themes and factors that drove existing research trajectories. Subsequently, the nocturnal cooling influence of an urban green-space was examined through direct observations and simulations from a microscale climate model (ENVI-Met 3.1) with an improved vegetation parameterization scheme. A distinct park cool island (PCI) of 0.7-3.6 °C was documented from traverse and model data with larger magnitudes closer to the surface. A key factor in the spatial expansion of PCI was advection of cooler air towards adjacent urban surfaces, especially at 0-1 m heights. Modeled results also possessed varying but reasonable accuracy in simulating temperature data, although some systematic errors remained. Finally, ENVI-Met generated xeriscaping scenarios in two residential areas with different surface vegetation cover (mesic vs. xeric), and examined resulting impacts on near-surface temperatures and outdoor thermal comfort. Desert-adapted low-water use shade trees may have strong UHI mitigation potential in xeric residential areas, with greater cooling occurring at (i.) microscales (~2.5 °C) vs. local-scales (~1.1 °C), and during (ii.) nocturnal (0500 h) vs. daytime periods (1700 h) under high xeriscaping scenarios. Conversely, net warming from increased xeriscaping occurred over mesic residential neighborhoods over all spatial scales and temporal periods. These varying results therefore must be considered by stakeholders when considering residential xeriscaping as a UHI mitigation method. / Dissertation/Thesis / Ph.D. Geography 2011

The winter urban heat island (UHI) has been suggested to reduce snowfall downwind of city centers due to localized energy and moisture flux variations, but previous research lacks spatial detail since it is primarily based on sparse surface observations. This project utilizes high-resolution radar data for twelve snow-only events, occurring from 1995-2008 and passing over the Minneapolis – St. Paul (MSP) urban area, to quantify the change in radar reflectivity values downwind of the city. Results show that five of the twelve snowfall events evaluated for the MSP urban area did not significantly decrease in summed decibel (dBZ) values downwind of the city center, and four of these events occurred on a day with a zero to positive urban-rural temperature gradient. Analysis of related atmospheric variables on these days suggest that atmospheric instability and convergence may play a critical role in urban snowfall modification.

The bulk of synoptic weather type research related to urban climate focuses on human health impacts; however, recent studies have begun to quantify urban heat island (UHI) magnitudes by weather type, or air mass classification. This study presents an analysis of UHI intensity through synoptic-scale air mass persistence during the spring season for four UHI-prone United States cities. Historical daily weather types for Birmingham, Alabama; Charlotte, North Carolina; Louisville, Kentucky; and St. Louis, Missouri were extracted from the Spatial Synoptic Classification database for 40 years from 1980 through 2019. Daily minimum surface air temperature data were downloaded from the Global Historical Climate Network to compute UHI. The historical daily weather type data were converted into a record of persistence, or the length of consecutive days that a synoptic weather type was in place at each location. A descriptive climatology of SSC weather types and UHI at each location was constructed before UHI magnitudes were segregated by day of persistence and examined for differences in intensity. Climatologically, the four urban areas experienced an increase in warm weather types at the expense of cool weather types throughout the study period. Specifically, the persistence of moist tropical weather types increased at a statistically significant rate at Birmingham, Charlotte, and Louisville, consistent with the theorized northward migration of the mid-latitude jet stream. Also evident is a statistically significant increase in UHI frequency and intensity at Birmingham, Charlotte, and Louisville during the study period. Results show that the moisture character of a weather type is an important differentiating factor in UHI intensification, as the mean UHI was found to increase with the persistence of dry weather types and decrease with the persistence of moist weather types, presumably reflecting differences in radiational heating and cooling with atmospheric moisture content. The most intense UHIs and the largest UHI magnitude increase by day of persistence are associated with dry weather types, which have become more frequent since 1980. The findings suggest that larger magnitude UHIs may become more common in the future should dry weather type persistence continue to increase. Higher urban temperatures put human health at risk due to a well-linked relationship between heat and mortality and morbidity rates. The effects of heat are cumulative; the more common persistent, oppressive days become, the larger the impact. / Master of Science / Most of the research related to variation in the warmth of an urban area relative to the surrounding rural area, or the urban heat island (UHI) effect, under varying air mass conditions (temperature and humidity) has focused on human health impacts. This study examines UHI intensity through regional-scale air mass persistence during the spring season in four UHI-prone United States cities. Historical daily air mass conditions in the form of weather types for Birmingham, Alabama; Charlotte, North Carolina; Louisville, Kentucky; and St. Louis, Missouri were downloaded from the Spatial Synoptic Classification database for the 40 years from 1980 to 2019. UHI values for each urban location were calculated using daily minimum air temperature data from the Global Historical Climate Network. A descriptive climatology of weather types and UHI magnitude at each of the four urban locations established long-term means and trends before analysis of UHI intensity through varying weather type residence times, or persistence. Time series analyses align with previous indications of an increasing persistence of weather types and an increase in the frequency of warm weather types at the expense of cool weather types during the spring season. An increase in both UHI frequency and intensity occurred through the study period at Birmingham, Charlotte, and Louisville. The mean intensity of the UHI was found to increase with the persistence of weather types of low humidity and to decrease with the persistence of moist weather types. The largest mean UHI and the largest UHI magnitude increase by day of persistence are associated with low humidity weather types, which have become more frequent since 1980. The impacts of heat are cumulative; persistently elevated temperatures are detrimental to human health.

Since climate change increases and changes constantly, it contributes to higher average temperatures, ice melting and has a great impact on our ecosystem. This will then lead to a warmer climate, which means increased precipitation and milder winters. One of the reasons to climate change is urbanization, meaning people moving to the cities. To succeed in changing the climate, international cooperation and common goals are required. At the northern part of Brynäs, in the municipality of Gävle, work is currently in progress around the area where the factory of Läkerol was once standing. The area continues to be rebuilt and the outcome will eventually be called Godisfabriken. There, amongst other, a car park will be built for the newly built homes. The aim of this study is to compare metal roofs, grey concrete roofs and green roofs within the two aspects of stormwater management and temperature. Then analyse which alternative of these three roofs would be most advantageous for the car park of Godisfabriken.   The focused roofs are green, metal and concrete. A green roof is when it's completely or partly covered by a layer of vegetation and metal roofs are different sheet roofs with steel and aluminium-zinc. Grey roofs are made of concrete which works as both floor and ceiling. A building's roof affects which air temperature the surroundings has with its slope, vegetation and surrounding buildings. Another problem with urbanization and a warmer climate is stormwater management, which means rain and melted snow from roofs, parking areas and other hard surfaces.   The method includes a literature study and calculations. The literature study gave research on temperature for all roofs as well as stormwater management for green roofs. Calculations were made for stormwater management and temperature with its flow, absorption, reflectance and heat transfer.   The literature study and the calculations showed that green roofs have a high SRI value of 80 while the remaining roof is at around 40. The higher SRI, the lower surface temperatures on the material. This is proven in both methods when green roofs according to the literature study received a maximum surface temperature of 38 °C and 48 °C. According to the literature study green roofs can preserve more than 50 % of the rainwater. They also had a water flow rate of 1.97 l/s, which is less than half of what the metal roof got in the calculations. Since green roofs had both low air and surface temperatures, as well as longer drainage times and most absorbed water, green roofs are a more suitable choice than metal and grey concrete. / Eftersom klimatförändringarna förändras och konstant ökar bidrar det till en högre medeltemperatur, att isen smälter och att ekosystemet påverkas. Detta kommer då leda till ett varmare klimat vilket medför ökad nederbörd och mildare vintrar. En av orsakerna är urbanisering vilket betyder att människor flyttar till städer. För att lyckas förändra klimatet krävs internationellt samarbete och gemensamma mål.   Vid norra Brynäs i Gävle kommun pågår just nu arbete runt området där Läkerolfabriken en gång stod. Gamla Läkerolområdet kommer slutligen bli Godisfabriken. Där kommer det uppföras ett parkeringshus till det nybyggda bostäderna. Syftet med denna studie är att jämföra metalltak, gråa betongtak och gröna tak inom de två aspekterna dagvattenhantering och temperatur, därefter analysera vilket alternativ av dessa tre tak som skulle vara mest fördelaktigt för Godisfabrikens parkeringshus.   De fokuserade taken var grönt-, metall- och betong tak. Ett grönt tak är då taket är helt eller delvis täckt av ett lager vegetation. Metalltak är olika plåttak med stål och aluminium-zink, gråa tak syftar på betongbjälklag som fungerar både som golv och tak. En byggnads tak påverkar vilken lufttemperatur omgivningen har, även takets lutning samt växtlighet och byggnaderna runt om. Ett annat problem med urbanisering och varmare klimat är dagvattenhanteringen, vilket innebär regn- och smältvatten från bland annat tak, parkeringsytor och andra hårdgjorda ytor.   Metoden innefattar en litteraturstudie samt beräkningar. Litteraturstudien gav forskning om temperatur för samtliga tak samt dagvattenhantering för gröna tak. Beräkningar genomfördes för dagvattenhantering och temperatur med dess flöde, absorption, reflektans och värmeöverföring.   Litteraturstudien och beräkningarna visade att gröna tak har ett högt SRI (Solar Reflectance Index) värde på 80 medan resterande tak låg på runt 40. Ju högre SRI desto lägre yttemperaturer på materialet. Detta bevisas i båda metodvalen då gröna tak enligt litteraturstudie fick en maximal yttemperatur på 38 °C och 48 °C enligt beräkningarna. De hade även ett dagvattenflöde på 1,97 l/s, vilket är mindre än hälften av vad metalltaken på 4,93 l/s fick vid beräkningarna och kan enligt litteraturstudien bevara mer än 50 % av regnvattnet. Då gröna tak hade både låga luft- och yttemperaturer samt längre avrinningstid och mest absorberat vatten visar det att gröna tak är ett mer lämpligt val än metall- och gråa betongtak.

Indiana University-Purdue University Indianapolis (IUPUI) / Extreme Heat Events are the leading cause of weather-related mortalities in the continental United States. Recent publications have suggested that vulnerability to extreme heat is impacted by variations in environmental and socioeconomic conditions, even across small spatial units. This study evaluated the usefulness of socioeconomic variables and satellite-derived environmental measurements as predictors of heat-related vulnerability during the July 14-17, 1995 heat wave in Chicago, IL. Geospatial analysis and statistical processes were implemented to identify and rank characteristics of vulnerable populations. Results suggest population density, educational attainment, age, and financial indicators are among the best predictors of heat vulnerability. Proximity to and intensity of Urban Heat Islands also appears to influence neighborhood vulnerability levels. Identification and mapping of vulnerability variables can distinguish locations of increased vulnerability during extreme weather conditions. These vulnerability maps could be utilized by city officials to plan and implement aid programs to specific high risk neighborhoods before an extreme heat event, and resulting health implications, occur. Continued study and implementation of these variables could also assist in identifying vulnerable populations in other urban environments, improve utilization of location-specific heat warning systems and impact new building policies to decrease vulnerability variables across the country.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Architecture / Doctoral / Doctor of Philosophy