Abstract. Global warming has already affected European rivers and their aquatic biota, and climate models predict an increase of temperature in central Europe over all seasons. We simulated the influence of expected changes in heat wave intensity during the 21st century on water temperatures of a heavily impacted pre-alpine Austrian river and analysed future mitigating effects of riparian vegetation shade on radiant and turbulent energy fluxes using the deterministic Heat Source model. Modelled stream water temperature increased less than 1.5 • C within the first half of the century. Until 2100, a more significant increase of around 3 • C in minimum, maximum and mean stream temperatures was predicted for a 20-year return period heat event. The result showed clearly that in a highly altered river system riparian vegetation was not able to fully mitigate the predicted temperature rise caused by climate change but would be able to reduce water temperature by 1 to 2 • C. The removal of riparian vegetation amplified stream temperature increases. Maximum stream temperatures could increase by more than 4 • C even in annual heat events. Such a dramatic water temperature shift of some degrees, especially in summer, would indicate a total shift of aquatic biodiversity. The results demonstrate that effective river restoration and mitigation require re-establishing riparian vegetation and emphasize the importance of land-water interfaces and their ecological functioning in aquatic environments.

-Stream water temperature limits the growth and survival of aquatic organisms; whereby riparian shading plays a key role in inhibiting river warming. This study explains the effects of riparian shading on summer water temperatures at a pre-alpine Austrian river, during heatwave and nonheatwave periods at low flow conditions. A vegetation-shading index was introduced for the quantification of riparian vegetation effects on water temperature. For maximum water temperatures, a downstream warming of 3.9°C was observed in unshaded areas, followed by a downstream cooling of 3.5°C in shaded reaches. Water temperature directly responded to air temperature and cloudiness. For an air temperature change of 2°C we modelled a water temperature change of 1.3°C for unshaded reaches, but lower changes for intensively shaded reaches. Similar daily variations at shaded reaches were up to 4°C lower than unshaded ones. This study gives clear evidence that for a medium-sized prealpine river, restoration practices should consider that discontinuity of riparian vegetation should be less than 6000 m; with more than 40% dense vegetation in order to minimize water temperature increases due to unshaded conditions. Keywords: riparian vegetation / vegetation-shading index / water temperature / river vegetation management / restorationRésumé -L'influence de la végétation rivulaire sur la température de l'eau pendant les conditions de faible débit dans une rivière de taille moyenne. La température de l'eau d'une rivière limite la croissance et la survie des organismes aquatiques ; de ce fait l'ombrage rivulaire joue un rôle clé dans la limitation du réchauffement des rivières. Cette étude analyse les effets de l'ombrage rivulaire sur les températures estivales de l'eau dans une rivière autrichienne préalpine, pendant les périodes de canicule et de non-canicule à faible débit. Un indice d'ombrage de la végétation a été introduit pour la quantification des effets de la végétation rivulaire sur la température de l'eau. Pour les températures maximales de l'eau, un réchauffement en aval de 3,9°C a été observé dans les zones non ombragées, suivi d'un refroidissement en aval de 3,5°C dans les zones ombragées. La température de l'eau a répondu directement à la température de l'air et à la nébulosité. Pour un changement de température de l'air de 2°C, nous avons modélisé un changement de température de l'eau de 1,3°C pour les zones non ombragées, mais des changements plus faibles pour les niveaux intensivement ombragés. Des variations quotidiennes semblables dans des zones ombragées étaient jusqu'à 4°C inférieures à celles non ombragées. Cette étude montre clairement que pour une rivière préalpine de taille moyenne, les pratiques de restauration devraient considérer que la discontinuité de la végétation riveraine doit être

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This paper examines the thermal properties of free-standing, ground-installed, south-facing crystalline and amorphous silicon photovoltaic modules, the remaining energy and the energy generation of the modules, in ideal and actual summer weather conditions. This work studies the algorithms in other studies used to describe the thermal processes occurring on the surface of photovoltaic modules. Using accurate devices and real, measured data, the deviations and the inaccuracies of theoretical approaches are investigated. The emphasis of the present study is to improve the simulation accuracy of the total emitted long-wave radiation at the module surface and to show the appropriate overall convection coefficient values for ground-mounted south-facing photovoltaic technologies. The innovative aspect of the present paper is an improved model resulting from an improved convective heat transfer and net long-wave radiation calculation. As a result of this research, algorithms describing the energy fluxes were developed. These algorithms have a 1-3% better accuracy of the net long-wave radiation calculations at the module surface. The rate of net energy exchange by convection at the module surface could be improved by 10-12% compared to the previous literature.

In this study we produce two urban development scenarios estimating potential urban sprawl and optimized development concerning building construction, and we simulate their influence on air temperature, surface temperatures and human thermal comfort. We select two heat waves representative for present and future conditions of the mid 21 st century and simulations are run with the Town Energy Balance Model (TEB) coupled online and offline to the Weather Research and Forecasting Model (WRF). Global and regional climate change under the RCP8.5 scenario causes an increase of daily maximum air temperature in Vienna by 7 K. The daily minimum air temperature will increase by 2-4 K. Changes caused by urban growth or densification mainly affect air temperature and human thermal comfort locally where new urbanisation takes place and does not occur significantly in the central districts. A combination of near zero-energy standards and increasing albedo of building materials on the city scale accomplishes a maximum reduction of urban canyon temperature achieved by changes in urban parameters of 0.9 K for the minima and 0.2 K for the maxima. Local scale changes of different adaptation measures show that insulation of buildings alone increases the maximum wall surface temperatures by more than 10 K or the maximum mean radiant temperature (MRT) in the canyon by 5 K. Therefore, measures to reduce MRT within the urban canyons like tree shade are needed to complement the proposed measures. This study concludes that the rising air temperatures expected by climate change puts an unprecedented heat burden on Viennese inhabitants, which cannot easily be reduced by measures concerning buildings within the city itself. Additionally, measures such as planting trees to provide shade, regional water sensitive planning and global reduction of greenhouse gas emissions in order to reduce temperature extremes are required.

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A simulation study reveals how open space design may mitigate local urban heat island effects.

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