The urban heat island (UHI) effect is a phenomenon that results in cities being warmer than the surrounding rural areas, due to a large amount of impervious surfaces. The purpose of this study is to evaluate the effectiveness of green roofs to mitigate the effects of solar energy on a building in the southern United States. In order to test the green roofs, temperatures were monitored inside and on top of unconditioned model buildings with green and with traditional roofs. Over the course of the study, the data collected showed that green roofs provided a significant benefit for the buildings by reducing daily high temperatures during summer and daily low temperatures during winter, while also reducing temperature fluctuation. The findings of this study suggest that a green roof will reduce indoor temperature and rooftop temperature, while providing several other benefits for city inhabitants such as reduced air temperature.

Numerous research studies have been conducted on the modification of weather and local climate by the urban environment. In studying the urban environment effects, researchers have investigated the urban heat island (UHI), anthropogenic cloud condensation nuclei, anthropogenic heat emissions and other factors. Many of these studies used data sampling networks, while other studies relied solely on computer modeling. This research has taken an approach between the sampling network studies (which were often limited in spatial density) and the pure computer model studies (which lacked the benefits of observational data) to investigate the Tampa Bay Region UHI. The research utilized inexpensive commercially available temperature logging sensors within a 525 km² study area. One hundred temperature logging sensors, deployed within the study area, generated in excess of 250,000 time and temperature data points for analysis. The large number of temperature sensors enabled the generation of detailed spatiotemporal maps of the Tampa Bay Region UHI. Analysis of the data revealed a significant relationship between the percentage of impervious surface in the study area and the intensity of the local UHI delta temperatures. In addition, the analysis identified the existence of micro UHIs within residential areas. These micro UHIs affected readings within the residential areas. In conjunction with the investigation of the relationship between the percentage of impervious surface and the generation of a UHI, wind speed's role as a moderating factor was also investigated. It was found that increases in wind speed are correlated with a lessoning of the observed UHI. Wind speeds above approximately 2 ms-1 exhibit a significant negative relationship to the development of a UHI. The results of this study add to the field of UHI research in subtropical environments.

Different environments exhibit varying temperatures, where generally areas with high amounts of vegetation, and consequently significant shading, tend to be cooler than regions dominated by dark buildings and black roofs. As a result, urban areas are generally expected to have higher temperatures in comparison to rural areas or forests. This phenomenon, known as urban heat island effect, can be visualized as a dome-shaped area of hot air that concentrates pollution and can influence the precipitation patterns of a region. This study aimed to examine the urban heat island effect in Linköping from 1984 to 2023, with a focus on analyzing the correlation between the prevalence of impermeable materials and changes in surface temperature using remote sensing and geographic information systems. The study also explored the potential for predicting surface temperatures in 2034 with spatial regression. The results indicated a close relationship between the extent of impermeable materials (indicative of urban land use) and the surface temperatures in Linköping over the study period. Both urban land use and areas with high surface temperatures increased from 1984 to 2023, independent of rising air temperatures. The geographic locations of high urban heat island values have remained largely unchanged over time, but their spatial distibution expanded from 1984 to 2023. The predictive analysis has demonstrated the possibility to predict surface temperatures in 2034, with emphasis on the pivotal role of the model and its explanatory variables. The final predictive model indicates a continuing upward trend in surface temperatures. This study has in summary added an extensive overview of the urban temperature changes in Linköping, identifying potential areas with particularly high surface temperatures historically and provided possible models for predicting trends in the future. / Olika miljöer uppvisar varierande temperaturer, där generellt områden med mycket vegetation, och därmed betydande skuggning, tenderar att vara svalare än regioner dominerade av mörka byggnader med svarta tak. Följaktligen förväntas urbana områden generellt ha högre temperaturer jämfört med landsbygdsområden eller skogsområden. Detta fenomen, känt som urban värmeöeffekt, kan förklaras som ett kupolformat område med förhöjda temperaturer som koncentrerar föroreningar, och som kan påverka regionala nederbördsmönster.  Denna studie syftade till att undersöka den urbana värmeöeffekten i Linköping från 1984 till 2023, med fokus på att analysera korrelationen mellan förekomsten av ogenomträngliga ytor och förändringar i yttemperatur med hjälp av fjärranalys och geografiska informationssystem. Landsat-satellitbilder har använts för att erhålla data för markanvändning/marktäcke, samt för markytans temperaturer under studieperioden. Studien undersökte också möjligheten att förutsäga yttemperaturer år 2034 med hjälp av två enkla prediktiva modeller i programvaran ArcGIS Pro: Multiskalig Geografiskt Viktad Regression (MGWR) och Forest-baserad Forecast.  Resultatet visade en nära relation mellan omfattningen av ogenomträngliga ytor (indikerade som urban markanvändning) och yttemperaturen i Linköping under studieperioden. Både urban markanvändning och områden med höga yttemperatur ökade från 1984 till 2023, oberoende av ökade lufttemperaturer. De geografiska positionerna för höga värmeövärden förblev i stort sett oförändrade över tid, men deras rumsliga fördelning expanderade från 1984 till 2023. Den prediktiva analysen visade att MGWR-modellen uppvisade begränsningar med de valda variablerna och dess samband till varandra. Däremot gav Forest-baserad Forecast-modellen ett mer tillförlitligt resultat, genom att utnyttja historiska yttemperaturer och data om markanvändning och marktäcke. Yttemperaturkartan för 2034 som generades av den senare modellen förutspår en ökning av områden med höga yttemperaturer (mellan 41 och 45 grader Celsius), och en bredare fördelning av temperaturer mellan 31 och 40 grader Celsius. Den prediktiva modellen indikerar en fortsatt uppåtgående trend i yttemperaturer. Sammanfattningsvis ger denna studie en omfattande översikt över urbana temperaturförändringar i Linköping, och identifierar potentiella områden med särskilt höga yttemperaturer historiskt och ger förslag för möjliga metoder för att förutsäga trender i framtiden.

Urban heat island is a phenomenon of different temperatures in cities compared to temperatures in the surrounding landscape. The intensity of this phenomenon can be influenced by the presence of vegetation in cities. There is evaluated the effect of vegetation on microclimate in various parts of the city České Budějovice in this thesis. The assessment is based on the evaluation of multispectral Landsat satellite images and thermal images, which were taken in-situ using thermal camera, and their statistical processing. The results show statistically significant differences in surface temperatures in the different areas of the city with a different amount of vegetation. Surface temperatures are significantly lower in areas with a large amount of vegetation than in areas without vegetation. Equally, selected vegetation surfaces have lower temperatures compared to anthropogenic surfaces, at least about 9 ° C.

The urban heat island (UHI) is a problem that is likely to be exacerbated by ongoing climate change, but it is often claimed that urban trees can mitigate it and hence adapt our cities to climate change. Many researchers have attempted to quantify the cooling effects of trees using modelling approaches. However, the major disadvantage of most of the models is that they consider all vegetation to act as a single saturated layer and that their effect is merely proportional to its surface cover. Therefore, they fail to take into account potential differences between tree species and the effect of different environmental and growing conditions. To address this issue four different studies were conducted in Manchester, UK from February, 2010 to December, 2012. The studies compared the growth and cooling abilities of several commonly planted urban tree species, and investigated a single species planted in a range of growing conditions: investigating the effect of urban soil compaction and aeration and also the effect of urbanization and simulated climate change in the rooting zone. Overall, our studies showed that species selection and growing conditions can substantially alter the evapotranspirational cooling provided by urban trees. Fast growing species such as Pyrus calleryana, with their dense and wide canopy can provide cooling up to 2.2 kW tree-1, 3-4 times that of Sorbus arnoldiana, which have a thinner and narrower canopy and a moderate growth rate. P. calleryana was also investigated under three contrasting growth conditions: in cut-out pits in pavements; in grass verges; and in pits filled with Amsterdam soil. Trees in the less compacted Amsterdam soil had grown almost twice as fast as those in pavements and also had better leaf physiological performance. Together with a longer growing season, and better uptake of soil nutrients and moisture, trees grown in Amsterdam soil provided evapotranspirational cooling of up to 7kW, 5 times higher than those grown in pavements. Another experiment in which P. calleryana trees were planted in 3 standard planting techniques with non-compacted load bearing soils and with or without permeable slabs showed that optimum cooling is not only dependent on preventing soil compaction but also on ensuring that the covering materials are permeable to oxygen. Trees in the open pits provided up-to 1 kW of cooling, compared to around 350 and 650 W by the small and large covered pits respectively. Our final experiment showed that urbanization can increase tree growth by 20-30%; however, despite being under more water stressed conditions trees grown in simulated climate change plots had 40% higher sap flux density, and hence cooling potential. The study suggested that at least with P. calleryana, transpirational cooling benefit might be enhanced in places like Manchester with increased soil temperature in future, but potentially at the expense of photosynthesis and carbon gain. Together these studies show that evaporative cooling of trees depends strongly on both species and growing conditions. If incorporated into regional and local energy exchange models our results can help us to quantify the magnitude and effectiveness of greenspaces in the city in adapting them to climate change.

Urbanization could have a negative impact on sustianble urban development due to the effect on human and ecosystem health. A possible strategy that can decrease temperature and create sustainable societies is through construction of parks in urban areas. The purpose of this study was to review and compare Malmö and Stuttgart municipalities work with the parks ecosystem services ability to regulate the temperature and local climate in order to achieve sustainable development. The result showed that the two municipalities had different methods for mitigation of Urban heat island (UHI) with ecosystem services. Malmö had an indirect approach regarding regulation of the temperature since there were no strategies. Stuttgart had a direct approach regarding regulation of the temperature since there were strategies for this. The study showed that it is important that parks are adjusted to manage the predicted climate changes in the future and thereby decrease the damage on the environment and human health.

The urban heat island, UHI, is a phenomenon that occurs in all cities. This phenomenon is an effect of us humans and the environments we have built. What happens in cities are that they re-emit the suns heat and other energies trapping them in this heat island.  The re-emitting happens through the pavement of the city, lack of greenery, roads and how the city is built and its geometry. Cities with skycrapers and of high density see a greater impact of the urban heat island where the wind flow is reduced and more heat is trapped and stored. The UHI is worst experienced in places with a very hot climate, such as the arid desert climate with extreme temperatures year round, like in the UAE and Dubai.  It is vital to tackle the UHI effect problem, because it puts people at danger. Many lives are shed each year due to heat strokes, that can be reduced if we take this problem into consideration when we design our cities. The UHI effect can be reduced by simple yet effective steps.

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Lors de la focalisation d’un laser femtoseconde ultra-intense [I>10¹⁶W/cm²] sur une cible solide, dès le début de l’impulsion le champ laser est suffisant pour totalement ioniser la surface de la cible. Le reste de l’impulsion est ensuite réfléchi dans la direction spéculaire par le plasma dense ainsi créé : c’est un miroir plasma. Le champ laser ultra-intense peut accélérer les électrons au sein du plasma à des vitesses relativistes. Certains sont éjectés vers le vide et ces miroirs plasmas sont ainsi des sources de faisceaux d’électrons énergétiques. De plus, ils rayonnent dans l’extrême ultra-violet (XUV) à chaque période laser, ce qui se traduit par de la génération d’harmoniques d’ordre élevé de la pulsation laser. L’objectif de cette thèse est de mieux comprendre l’interaction laser-plasma sur miroirs plasmas à l’aide de la caractérisation de ces deux observables physiques qui en sont issues : les faisceaux d’électrons relativistes et les faisceaux d’harmoniques d’ordre élevé. Une première partie traite de la mesure des faisceaux harmoniques. Du fait des conditions physiques extrêmes d’interaction, la détection ne peut se faire qu’à une distance macroscopique de la cible. Ainsi la caractérisation des propriétés angulaires de ces faisceaux (réalisée en fonction des conditions d’interaction au cours de travaux précédents) ne fournit que des informations partielles sur l’interaction en elle-même. La ptychographie, une technique de mesure par diffraction cohérente où une sonde est diffractée par un objet, est ici transposée à la génération d’harmoniques sur miroirs plasmas grâce à la micro-structuration optique du plasma à la surface de la cible. Les champs sources harmoniques sont ainsi reconstruits en amplitude et en phase spatiales directement dans le plan cible. Grâce à ces mesures dans différentes conditions d’interaction, des modèles théoriques analytiques d’interaction en régime non relativiste [I<10¹⁸W/cm²] et relativiste [I>10¹⁸W/cm²] développés précédemment sont validés expérimentalement. Une seconde partie de cette thèse est consacrée à l’étude expérimentale des propriétés angulaires et en énergie des faisceaux d’électrons relativistes issus des miroirs plasmas. Une étude théorique et numérique, permet de prouver que ces mesures sont la première observation claire de l’accélération d’électrons relativistes par laser dans le vide (VLA). Enfin, l’étude simultanée des efficacités de génération des faisceaux d’électrons et d’harmoniques montre une corrélation nette entre les deux processus en régime relativiste. / When focusing an ultra-intense femtosecond laser pulse [I>10¹⁶W/cm²] onto a solid target, this target is ionized at the very beginning of the laser pulse. The resulting dense plasma then reflects the laser in the specular direction: it is a plasma mirror. The ultra-intense laser field can accelerate electrons within the plasma at relativistic speeds. Some are ejected towards the vacuum and these plasma mirrors are therefore sources of relativistic electron beams. Moreover, at each optical cycle they radiate in the form of extreme ultraviolet light, resulting in the generation of high-order harmonics of the laser frequency (HHG). The objective of this PhD is to understand laser-plasma interaction though the characterization of high-order harmonics and relativistic electron beams generated from plasma mirrors. The first part deals with harmonic beam measurement. Due to the extreme physical conditions during the interaction, detection can only be performed at macroscopic distance from target. Thus, the characterization of the harmonic beams’ angular properties (carried out as a function of interaction conditions in previous works) only provides partial information on the interaction itself. A technique of coherent diffraction imaging, named ptychography, which consists of diffracting a probe onto an object, is transposed to HHG on plasma mirrors by optically micro-structuring the plasma on a target surface. Harmonic fields are then reconstructed spatially in amplitude and phase directly in the target plane. Thanks to this measurement in different interaction conditions, previously developed theoretical analytical models in non-relativistic regime [I<10¹⁸W/cm²] and relativistic regime [I>10¹⁸W/cm²] are experimentally validated. The second part of the PhD is dedicated to the experimental characterization of angular and spectral properties of relativistic electron beams. A theoretical and numerical study shows that this constitutes the first clear observation of vacuum laser acceleration (VLA). Finally, a simultaneous study of harmonic and electron signals highlights a strong correlation between both processes in the relativistic regime.

Syftet med studien var att kartlägga urban heat island [UHI]- och klimatanpassningsåtgärder som London och Stockholm arbetat med för att reducera UHI-effekten i respektive stad. Eftersom London upplever en högre UHI-effekt har de därmed kommit längre i deras arbete, studien fokuserade därför även på att förstå vad som är bakgrunden till att Stockholm brister i sitt arbete. En semikvalitativ innehållsanalys användes för att besvara frågeställningarna. Tre statliga dokument från respektive stad analyserades genom kodning och kategorisering. Åtgärderna som hittades graderades utifrån typ av åtgärd (åtta olika kategorier) och nivå på åtgärd (planerad, pågående eller genomförd). Resultatet visade att London har ett mer utförligt och proaktivt arbete med att motverka UHI än Stockholm, dels för att de lyfte budget och investeringar för deras olika åtgärder. Projekten är även större och omfattar fler områden än Stockholm. Stockholm har därmed mycket att hämta från Londons UHI- och klimatanpassningsarbete. Trots att Stockholm hade fler åtgärder är det inte lika omfattande och utvecklade jämfört med London som hade större projekt, program och policys. Resultatet visade att fler åtgärder genomförts i London. Det framgick att attityden skiljer sig åt mellan städerna. Stockholm måste förstå allvaret och borde påskynda sitt arbete genom att lägga ner mer resurser och samarbeta med aktörer för att säkerställa att projekten uppfylls och underhålls. / The purpose of this study was to map the urban heat island [UHI] and climate adaptation measures that London and Stockholm are implementing to reduce the UHI effect. London experiences a higher UHI effect, and therefore are more advanced in their work in contrast to Stockholm. The study employed a semi-qualitative content analysis, in addition with three government documents from each city which were analysed through coding. The measures found were categorised according to type of measure (eight different categories) and level of measure (planned, ongoing or implemented). The results showed that London has a more comprehensive and proactive approach to tackling UHI than Stockholm, through raising budgets and investments for their various actions, larger projects, and projects that cover more areas than Stockholm. Stockholm can utilise the development of London's UHI and climate adaptation work to better fix their issue. Although Stockholm has more measures, these are not as extensive and developed compared to London, which has larger projects, programmes and policies, in addition with more active measures being implemented in London. From the analysis it was evident that attitudes differ between Stockholm and London. Stockholm needs to understand the seriousness and should accelerate its work by putting more resources and collaborating with stakeholders to ensure that projects are fulfilled and maintained.