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.

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.

A combination of the urban heat island effect and a rising temperature baseline resulting from global climate change inequitably impacts socially vulnerable populations residing in urban areas. This dissertation examines distributional inequity of exposure to urban heat by socially disadvantaged groups and minorities in the context of climate justice. Using Cutter’s hazards-of-place model, variables indicative of social vulnerability and biophysical vulnerability are statistically tested for their associations. Biophysical vulnerability is conceptualized utilizing a urban heat risk index calculated from summer 2010 LANDSAT imagery to measure land surface temperature , structural density through the normalized difference built-up index, and vegetation abundance through the normalized difference vegetation index. A cross-section of twenty geographically distributed metropolitan statistical areas (MSAs) in the U.S. are examined using census derived variables at the tract level. The results of bivariate correlation analysis, ordinary least squares regression, and spatial autoregression analysis indicate consistent and significant associations between greater social disadvantage and higher urban heat levels. Multilevel modeling is used to examine the relationship of MSA-level segregation with tract-level minority status and social disadvantage to higher levels of urban heat. Segregation has a significant but varied relationship with the variables, indicating that there are inconsistent associations with urban heat due to differing urban ecologies. Urban heat and social vulnerability present a varying landscape of thermal inequity in different urban areas, associated in many cases with residential segregation.

Urbanisation alters the hydrologic response of a catchment, resulting in increased runoff rates and volumes, and loss of infiltration and base flow. Quantification of uncertainties is important in hydrologic designs of urban infrastructure. Major sources of uncertainty in the Intensity Duration Frequency (IDF) relationships are due to insufficient quantity and quality of data leading to parameter uncertainty and, in the case of projections of future IDF relationships under climate change, uncertainty arising from use of multiple General Circulation Models (GCMs) and scenarios. The work presented in the thesis presents methodologies to quantify the uncertainties arising from parameters of the distribution fitted to data and the multiple GCMs using a Bayesian approach. High uncertainties in GEV parameters and return levels are observed at shorter durations for Bangalore City. Twenty six GCMs from the CMIP5 datasets, along with four RCP scenarios are considered for studying the effects of climate change. It is observed that the uncertainty in short duration rainfall return levels is high when compared to the longer durations. Further it is observed that parameter uncertainty is large compared to the model uncertainty. Disaggregation of precipitation extremes from larger time scales to smaller time scales when the extremes are modeled with the GPD is burdened with difficulties arising from varying thresholds for different durations. In this study, the scale invariance theory is used to develop a disaggregation model for precipitation extremes exceeding specified thresholds. A scaling relationship is developed for a range of thresholds obtained from a set of quantiles of non-zero precipitation of different durations. The disaggregation model is applied to precipitation datasets of Berlin City, Germany and Bangalore City, India. From both the applications, it is observed that the uncertainty in the scaling exponent has a considerable effect on uncertainty in scaled parameters and return levels of shorter durations. A Bayesian hierarchical model is used to obtain spatial distribution of return levels of precipitation extremes in urban areas and quantify the associated uncertainty. Applicability of the methodology is demonstrated with data from 19 telemetric rain gauge stations in Bangalore City, India. For this case study, it is inferred that the elevation and mean monsoon precipitation are the predominant covariates for annual maximum precipitation. For the monsoon maximum precipitation, it is observed that the geographic covariates dominate while for the summer maximum precipitation, elevation and mean summer precipitation are the predominant covariates. In this work, variation in the dependence structure of extreme precipitation within an urban area and its surrounding non-urban areas at various durations is studied. The Berlin City, Germany, with surrounding non-urban area is considered to demonstrate the methodology. For this case study, the hourly precipitation shows independence within the city even at small distances, whereas the daily precipitation shows a high degree of dependence. This dependence structure of the daily precipitation gets masked as more and more surrounding non-urban areas are included in the analysis. The geographical covariates are seen to be predominant within the city and the climatological covariates prevail when non-urban areas are added. These results suggest the importance of quantification of dependence structure of spatial precipitation at the sub-daily timescales, as well as the need to more precisely model spatial extremes within the urban areas. The work presented in this thesis thus contributes to quantification of uncertainty in precipitation extremes through developing methodologies for generating probabilistic future IDF relationships under climate change, spatial mapping of probabilistic return levels and modeling dependence structure of extreme precipitation in urban areas at fine resolutions.