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To estimate the effect of vegetation stress and changes in biogenic volatile organic compound (BVOC) emissions on urban ozone (O3) levels we perform a systematic, observation-based analysis of the relationship between formaldehyde (HCHO) mixing ratios, meteorological parameters, measurement-based drought indicators and O3 over the central European city of Vienna, Austria. In addition, numerical models SURface EXternalisée (SURFEX), Model of Emissions of Gases and Aerosols from Nature (MEGAN) Vers.2.1 and 3 and MOdèle de Chimie A Grande Echelle (MOCAGE) are combined to estimate the soil moisture, the spatial distribution and drought response of isoprene emissions, and the resulting distribution of HCHO in the atmosphere. To analyse the effect of drought during spring and summer we contrast observations during dry and reference years. Our results show that the observed HCHO can be explained using the simulated isoprene emissions as well as observed and simulated vegetation drought responses. HCHO mixing ratios differ strongly between dry and reference seasons. Spring-time precipitation deficits facilitate reduced HCHO mixing ratios due to delayed and weakened plant growth. In consequence also O3 burdens are lowered due to reduced BVOC precursor emissions. These reductions occur despite radiation levels being higher than during the reference year, illustrating the strong potential of spring-time BVOC emissions to modulate urban O3 burdens. Conversely, during summer elevated O3 levels occur during local drought conditions. These are driven by advected isoprene originating from nearby forest areas, which are not affected by drought. Our results regarding elevated summer-time O3 burdens under vegetation heat and drought stress are in good agreement with previous work.

Imidazolium-based ionic liquids (ILs) have unique and tunable features with high potential in industrial use. However, the utilization of the ILs in industrial processes has recently arisen the question of their disposal and the effect on the environment. Therefore, in the present study, we investigated the effect of two commercial imidazolium-based ILs, 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) and 1-decyl-3-methylimidazolium chloride ([Dmim][Cl]) on the growth and chemical composition of widely grown vegetables - tomato and cucumber. Different concentrations (10, 100 or 1000 mg L−1) of [Bmim][Cl] and [Dmim][Cl] were applied to the soil on which tomato was cultivated. After the harvest of tomato fruits, the same soil was used to grow and analyze the growth and chemical composition of cucumber. ILs significantly reduced shoot biomass and yield of tomato and significantly changed concentrations of N, K, Ca, Fe and Mn in the leaves, whereas concentrations of P, Cu and Zn were at the level of respected controls. The number of fruits of cucumber, grown on the soil previously treated with ILs, was significantly reduced along with yield, and mineral composition of leaves was significantly altered, with the exception to Cu. [Dmim][Cl] in general affected both tomato and cucumber more than [Bmim][Cl]. The application of IL with a longer alkyl substituent ([Dmim][Cl]) increased the temperature inside the tomato canopy and accelerated the senescence of plants.

Knowing the solar radiation fluxes inside an urban canyon is of interest for different purposes: e.g. urban climatology and studies of human thermal comfort and gaining relevance for future renewable energy generation in an urban environment using photovoltaic systems. For the latter, mainly rooftops are of interest, but studies started to extend towards the solar resources on building facades. However, the reflected solar radiation from the ground is either neglected or estimated using simplifications that lead to overestimation. SEBEpv (Solar Energy on Building Envelope – photovoltaic) is a new tool attempting to provide better estimates for the radiation reflected from the ground onto facades. It is primarily intended for the urban environment where the ground-view is very limited. SEBEpv delivers 3D results based on digital surface models of the environment. Furthermore, an optional PV model was added in order to address the simplified of estimation of reflected radiation when modelling photovoltaic (PV) yields. SEBEpv delivers quite good estimates for the solar radiation compared to the measurements. The simulated irradiance shows an RMSE of 28.7 W/m2 compared to the measured irradiance and has a bias close to zero. This is about half the RMSE shown by the predecessor tool SEBE. The measured total irradiation over two years shows a bias of about 7%, which is likely to be a result of the limited angular resolution of the shading algorithm. Overall, SEBEpv seems to be a promising tool, accounting for reflected radiation in urban environments.

Since May 2017 and August 2018, two ground-based MAX-DOAS (multi-axis differential optical absorption spectroscopy) instruments have been continuously recording daytime spectral UV–visible measurements in the northwest (University of Natural Resources and Life Sciences (BOKU) site) and south (Arsenal site), respectively, of the Vienna city center (Austria). In this study, vertical aerosol extinction (AE) profiles, aerosol optical depth (AOD), and near-surface AE are retrieved from MAX-DOAS measurements recorded on cloud-free days applying the Bremen Optimal estimation REtrieval for Aerosols and trace gaseS (BOREAS) algorithm. Measurements of atmospheric profiles of pressure and temperature obtained from routinely performed sonde ascents are used to calculate box-air-mass factors and weighting functions for different seasons. The performance of BOREAS was evaluated against co-located ceilometer, sun photometer, and in situ instrument observations covering all four seasons. The results show that the vertical AE profiles retrieved from the BOKU UV–visible MAX-DOAS observations are in very good agreement with data from the co-located ceilometer, reaching correlation coefficients (R) of 0.936–0.996 (UV) and 0.918–0.999 (visible) during the fall, winter, and spring seasons. Moreover, AE extracted using the lowest part of MAX-DOAS vertical profiles (up to 100 m above ground) is highly consistent with near-surface ceilometer AE (R>0.865 and linear regression slopes of 0.815–1.21) during the fall, winter, and spring seasons. A strong correlation is also found for the BOREAS-based AODs when compared to the AERONET ones. Notably, the highest correlation coefficients (R=0.953 and R=0.939 for UV and visible, respectively) were identified for the fall season. While high correlation coefficients are generally found for the fall, winter, and spring seasons, the results are less reliable for measurements taken during summer. For the first time, the spatial variability of AOD and near-surface AE over the urban environment of Vienna is assessed by analyzing the retrieved and evaluated BOREAS aerosol profiling products in terms of different azimuth angles of the two MAX-DOAS instruments and for different seasons. We found that the relative differences of averaged AOD between different azimuth angles are 7–13 %, depending on the season. Larger relative differences of up to 32 % are found for near-surface AE in the different azimuthal directions. This study revealed the strong capability of BOREAS to retrieve AE profiles, AOD, and near-surface AE over urban environments and demonstrated its use for identifying the spatial variability of aerosols in addition to the temporal variation.

We investigate terrain effects on short-wave radiation measurements at Kanzelhohe Observatory (KSO), a mountainous radiation monitoring site in the Austrian Southern Alps, using three-dimensional (3-D) radiative transfer (RT) modeling and observations. The magnitude of terrain effects on global radiation is experimentally assessed through the comparison of 10-min measurement segments ex−/including terrain reflected radiation. The reflected component is ex−/included in global solar irradiance (GLO) measurements through a horizon shaped metal frame raised/lowered in 10-min intervals. Additionally we assess terrain influence in 3-D RT model simulations performed with an updated version of GRIMALDI, allowing for digital elevation model inclusion. The DEM used for terrain representation is the one arc second Shuttle Radar Topography Mission (SRTM) digital elevation model. For GRIMALDI simulations we consider an area averaged albedo of 0.30 for summer and 0.36 for winter (0.30 for forests and 0.90 for fresh snow), respectively. The influence of the horizon and surface albedo on a grid cell of interest (KSO location) is derived through comparison of the solar irradiance incident on a domain grid cell surface (SI-GCS) with SI-GCS reduced for the reflected component. Applying a 2σ threshold for the significance of terrain effects in GLO measurements, we find no significant influence of the surrounding during summertime. Also during wintertime, we find for the vast majority of observational increments no significant influence of the surrounding. Above a 2σ threshold, exceedances are small, on average 0.2 W m−2. Differences between 3-D RT model simulations including and excluding terrain effects are small during winter conditions, i.e. always below 1% and never exceeding 1 W m−2. Slightly larger differences are found for 3-D RT simulations including/excluding the reflected component during summertime, reaching at solar noon up to 6.1 W m−2. Both observations and model simulations indicate that KSO is well suited for radiation monitoring as terrain effects are small (close to negligible considering instrument specifications) throughout the year.

Within the project VINDOBONA (VIenna horizontal aNd vertical Distribution OBservations Of Nitrogen dioxide and Aerosols), a method was developed to retrieve the spatial distribution of trace gases using data from three ground based MAX-DOAS instruments and was applied on the example of NO2. At three different locations in Vienna (Austria) MAX-DOAS instruments were installed performing measurements in the visible and UV spectral range. Currently, each instrument is set up to determine the column densities in different azimuthal directions and low elevation angles within approximately a horizontal plane. The different lines of sight of the three instruments intersect horizontally and can be used to estimate the horizontal spatial distribution of trace gases. With the knowledge of vertical profiles, even the vertical distribution can be estimated using this method. The intersections of the different lines of sight define segments along the slant columns for which the mass concentrations can be estimated. Knowledge about the vertical profiles for a chosen trace gas can be used to correct the retrieved trace gas concentration to specific altitudes above ground. Such corrections are also required since the three instruments were set up at different heights above ground, at different altitudes relative to sea level and with different elevation angles of the lowest viewing direction. One open issue for the retrieval process is the terrain in Vienna in combination with the prevailing wind condition that impacts the horizontal and vertical trace gas distribution and make the retrieval challenging.

Visibility and visual contrast depend on several factors such as aerosol concentration, fog attenuation and humidity as well as gas characteristics. Usually, visibility is determined by observers or by visiometers. Routine web cam photographs of Vienna have been performed for 2 years from the meteorological measurement platform situated on the roof of one of the buildings of University of Natural resources and Life Sciences overlooking the whole city of Vienna. Photographs are taken every 30 minutes in 6 different azimuthal directions. In the following study, we used routine web cam photographs digitalization to study the correlation between the ratio of some RGB channels as well as intensity fluctuations and the aerosol optical depth and on site particulate matter measurements. We first selected only photographs taken on clear sky daysFor ground truth data, we used CIMEL sun photometer data of aerosol optical depth and liquid water content, relative humidity from routine measurements from our measurement platform as well as in situ measurements of particulate matter (PM10) performed by the air quality monitoring network of the city of Vienna.First, the correlation between the contrast in a horizontal line and the aerosol amounts in the atmosphere and particulate matter concentration as a function of time of the day and azimuthal direction was investigated. We then examined the correlation between the blue to red ratio in a vertical and horizontal line with the aerosol amounts and particulate matter concentration in the atmosphere.Results obtained showed at some azimuth angles and time of the day correlation coefficient R squared of up to 0.85 between horizontal line contrast and in situ PM 10 and between vertical line blue to red ratio and CIMEL aerosol optical depths measurements.

Climate change threatens to exacerbate existing problems in urban areas arising from the urban heat island. Furthermore, expansion of urban areas and rising urban populations will increase the numbers of people exposed to hazards in these vulnerable areas. We therefore urgently need study of these environments and in-depth assessment of potential climate adaptation measures.We present a study of heat wave impacts across the urban landscape of Vienna for different future development pathways and for both present and future climatic conditions. We have created two different urban development scenarios that estimate potential urban sprawl and optimized development concerning future building construction in Vienna and have built a digital representation of each within the Town Energy Balance (TEB) urban surface model. In addition, we select two heat waves of similar frequency of return representative for present and future conditions (following the RCP8.5 scenario) of the mid 21st century and use the Weather Research and Forecasting Model (WRF) to simulate both heat wave events. We then couple the two representations urban Vienna in TEB with the WRF heat wave simulations to estimate air temperature, surface temperatures and human thermal comfort during the heat waves. We then identify and apply a set of adaptation measures within TEB to try to identify potential solutions to the problems associated with the urban heat island.Global and regional climate change under the RCP8.5 scenario causes the future heat wave to be more severe showing an increase of daily maximum air temperature in Vienna by 7 K; the daily minimum air temperature will increase by 2-4 K. We find that changes caused by urban growth or densification mainly affect air temperature and human thermal comfort local to where new urbanisation takes place and does not occur significantly in the existing central districts.Exploring adaptation solutions, we find that 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 of 0.9 K for the minima and 0.2 K for the maxima. Local scale changes of different adaption 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, additional adaptation 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.We are now actively seeking to apply this set of tools to a wider set of cases in order to try to find effective solutions to projected warming resulting from climate change in urban areas.

Within the scope of the VINDOBONA (VIenna horizontal aNd vertical Distribution OBservations Of Nitrogen dioxide and Aerosols) project, spectral UV/vis measurements at selected viewing directions are performed with three MAX-DOAS (Multi AXis Differential Optical Absorption Spectroscopy) instruments, which are located in the northeast, northwest, and south of the city center of Vienna, Austria. The selection of viewing directions of the three instruments was chosen in a way to provide data for the retrieval of horizontal and vertical trace gas and aerosol distributions, in particular over the urban core.In the present work, the profile retrieval algorithm BOREAS (Bremen Optimal estimation REtrieval for Aerosols and trace gaseS) is used to retrieve aerosol and NO2 vertical profiles as well as accompanying parameters aerosol optical depth, tropospheric NO2 vertical columns (TVC NO2), and near-surface NO2 on days with cloudless conditions. The retrieval results are compared with co-located ceilometer, sun photometer, surface air quality, and TVC NO2 measurements, with the latter being obtained by applying the geometrical approximation and converting zenith-sky NO2 measurements.

While capabilities in urban climate modeling have substantially increased in recent decades, the interdependency of changes in environmental surface properties and human (dis)comfort have only recently received attention. The open-source solar long-wave environmental irradiance geometry (SOLWEIG) model is one of the state-of-the-art models frequently used for urban (micro-)climatic studies. Here, we present updated calculation schemes for SOLWEIG allowing the improved prediction of surface temperatures (wall and ground). We illustrate that parameterizations based on measurements of global radiation on a south-facing vertical plane obtain better results compared to those based on solar elevation. Due to the limited number of ground surface temperature parameterizations in SOLWEIG, we implement the two-layer force-restore method for calculating ground temperature for various soil conditions. To characterize changes in urban canyon air temperature (Tcan), we couple the calculation method as used in the Town Energy Balance (TEB) model. Comparison of model results and observations (obtained during field campaigns) indicates a good agreement between modeled and measured Tcan, with an explained variance of R2 = 0.99. Finally, we implement an energy balance model for vertically mounted PV modules to contrast different urban surface properties. Specifically, we consider (i) an environment comprising dark asphalt and a glass facade and (ii) an environment comprising bright concrete and a PV facade. The model results show a substantially decreased Tcan (by up to − 1.65°C) for the latter case, indicating the potential of partially reducing/mitigating urban heat island effects.

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.

Theoretical and Applied Climatology, 133, ISSN:0177-798X, ISSN:1434-4483

The greening of shotcrete walls represents a major challenge due to the extreme environmental conditions for plants and its technical implementation aiming to establish a sustainable vegetation layer. The objective of the study was to assess the performance of an innovative ‘Green Wall’ system (double-layered, integrated irrigation, filled with excavation material, application on vertical inclination) with respect to its microclimatic characteristics. The measurement campaign was conducted from June 2015 to September 2016 in Plon (Steinach am Brenner, Tyrol, Austria). Microclimatic parameters (air temperature, air humidity, short-wave radiation, substrate temperature and wall surface temperature) were investigated by sensors installed in different layers of the greenery system, as well as in a control area (bare concrete wall). Results indicated a pronounced insulation effect of the ‘Green Wall’ system during summer and wintertime. Analyses in July 2015 (30% vegetation cover) and July 2016 (100% vegetation cover) indicated that reductions of temperature fluctuations were predominately attributable to the substrate layers of the greenery system and less to the vegetation cover. Furthermore, reductions of albedo (reflectivity) and heat stress were achieved. In conclusion, the ‘Green Wall’ system is a promising technique with positive effects regarding temperature and radiation as well as human thermal sensation and therefore recommendable for use also in urban areas. In rural areas it helps to optimize landscape aesthetics, as even vertical slopes can be greened.

This study investigates the effects of ambient meteorology on the accuracy of radiation (R) measurements performed with pyranometers contained in various heating and ventilation systems (HV-systems). It focuses particularly on instrument offsets observed following precipitation events. To quantify pyranometer responses to precipitation, a series of controlled laboratory experiments as well as two targeted field campaigns were performed in 2016. The results indicate that precipitation (as simulated by spray tests or observed under ambient conditions) significantly affects the thermal environment of the instruments and thus their stability. Statistical analyses of laboratory experiments showed that precipitation triggers zero offsets of −4 W m−2 or more, independent of the HV-system. Similar offsets were observed in field experiments under ambient environmental conditions, indicating a clear exceedance of BSRN (Baseline Surface Radiation Network) targets following precipitation events. All pyranometers required substantial time to return to their initial signal states after the simulated precipitation events. Therefore, for BSRN-class measurements, the recommendation would be to flag the radiation measurements during a natural precipitation event and 90 min after it in nighttime conditions. Further daytime experiments show pyranometer offsets of 50 W m−2 or more in comparison to the reference system. As they show a substantially faster recovery, the recommendation would be to flag the radiation measurements within a natural precipitation event and 10 min after it in daytime conditions.

River morphology, field study. Riparian vegetation, field study. Stream water temperature, oberservations and predictions. Near stream microclimate, oberservations and predictions. Fish species and assemblages, sampling. Benthic invertebrate abundance and diversity, sampling. Initially only stream water observations, predictions of the river Pinka and corresponding input data for extreme heat wave events used in Trimmel et al. (2016b) are available for download. Other parts of the data set may be included later after they have been published.

Die Anforderungen an Verkehrsflachen im urbanen Bereich sind vielfaltig und steigen kontinuierlich. Von Bedeutung fur die Bewohner ist die Reduktion von urbanen Warmeinseln bzw. „Heat Islands”, welche aufgrund ihrer erhohten Temperatur das Stadtklima negativ beeinflussen. Auf Basis der Untersuchung wurde festgestellt, dass die Oberflachentemperatur und das allgemeine Temperaturniveau im innerstadtischen Bereich (dargestellt am Beispiel Wien) durch Ausfuhrung heller Verkehrsflachen deutlich reduziert und auch die Sichtbarkeit von Verkehrsteilnehmern bei gleicher Ausleuchtung in der Nacht wesentlich verbessert werden kann. Als effiziente Sanierungsmethode eignet sich hier das System Whitetopping besonders gut, da mit dieser Methode sowohl die Tragfahigkeit als auch die Helligkeitseigenschaften von urbanen Verkehrsflachen einfach und kostengunstig verbessert werden konnen. Das Ersetzen von Asphaltstrasen durch Strasen mit einem Betonbelag mit einer Albedo gleich 0,5 wurde zu einer Abnahme der taglichen Lufttemperatur im Sommer um ca. 1 °C fuhren. Auch die Modellsimulationen der Lufttemperatur uber eine 150 m × 150 m grose homogene Flache zeigen eine Abnahme der Temperatur um 1 °C uber Flachen in Whitetopping-Ausfuhrung verglichen zu Asphalt. Da Strasen einen Anteil von ca. 10 % der Gesamtflache einer Stadt in Anspruch nehmen, konnen hier effiziente und langfristige Masnahmen zur Verbesserung des Mikroklimas sowie der Erhohung der Verkehrssicherheit gesetzt werden.

In the present paper, the climate cooling potential of technical snow making on ski slopes is investigated with regard to radiative forcing. It is well-known, that snow shows a higher degree of reflection compared to other ground surfaces. During snow-poor winters, guaranteeing snow covered ski slopes by using snow making may therefore lead to an increase in the albedo of a mountainous region. Since increasing albedo engenders a negative radiative forcing, the cooling potential of snow production on ski slopes is of particular relevance in the context of the current climate debate. Investigations were however generally performed for flat surfaces. Several studies nevertheless demonstrated that the topography leads to a substantial decrease in the mean albedo of a given region. This is attributable to shading effects and to slope inclinations. The present study was therefore dedicated to the accurate simulation of the impact of the albedo increase of ski slopes on the mean albedo and on the resulting change in shortwave radiative budget of a chosen mountainous region. We used therefore a state of the art 3-dimensional radiative transfer model. The investigations were carried out for the skiing area Saalbach-Hinterglemm in Austria. Broadband snow albedo values between 0.61 and 0.62 in cloudless conditions and 0.64 and 0.65 in cloudy conditions for solar zenith angle (sza) between 30 and 80 degrees were used for the simulations. An uncertainty of ±0.17 was taken into account. First a sensitivity study was performed, that showed a substantial decrease in the mean albedo of the ski slopes as a function of slope inclination. A strong impact of topography and of surrounding trees on the mean albedo of the ski slopes of up to 40% and 14% respectively was found at high sza under clear sky conditions. Compared to snow free conditions an increase in albedo between 0.18 and 0.36 was observed, the higher values for smaller sza and assuming no trees in the surroundings. Only related to the ski slopes a radiative forcing between −7 and −35 W/m2 was obtained. If the long-term snow cover conditions were taken into account, snow making lead to a change in albedo, only, in March and April. The increase in albedo was just below 0.10 in April and 0.02 in March, resulting in a radiative forcing around −12 W/m2 and around −1.5 W/m2 respectively. Though, in order to analyze an eventual cooling effect on climate the whole carbon footprint related to the production of technical snow making shall be determined.

Vorliegende transdisziplinare Studie untersuchte im Rahmen des ACRP Projektes BIO_CLIC die Wirkung der Ufervegetation auf das Wassertemperaturregime sowie die Interaktionen mit aquatischen Organismen von kleinen und mittelgrosen Flussen am Beispiel von Lafnitz und Pinka. Ziel ist es, relevante Zusammenhange zu analysieren und darzustellen, um daraus Managementmasnahmen und Anpassungsstrategien entwickeln zu konnen. Die beiden Flusse befinden sich im Sudosten Osterreichs, einer Region, die nach derzeitigem Wissensstand mit relativ starken Auswirkungen des Klimawandels zu rechnen hat. Es ist davon auszugehen, dass der Klimawandel die Wassertemperaturen nicht nur steigen lasst, sondern dass auch haufiger Hitzeperioden auftreten konnen. Im Zuge der vorliegenden Arbeit wurden die thermischen Habitate sowie die Ufervegetation erfasst und die longitudinale Verbreitung von Fischen sowie der benthischen Evertebraten-Fauna (gewasserbodenbewohnende wirbellose Lebensgemeinschaft) analysiert. Dabei stellt die Lafnitz, vor allem im Mittellauf, ein weitgehend naturnahes Gewasser dar, wahrend die Pinka starke anthropogene Beeintrachtigungen aufweist. Eine Synthese von Wassertemperatur und Ufervegetation mit der Fisch- und wirbellosen benthischen Fauna, in Form von „Fact Sheets“, zeigt sehr grose Unterschiede an sechs verschiedenen „Hot Spots“ und unterstreicht die Bedeutung abiotischer gewassertypspezifischer Parameter fur aquatische Lebensgemeinschaften. Die globale Erwarmung zeigt heute bereits Auswirkungen auf Fliesgewassersysteme und wird in Zukunft diese Okosysteme und ihre Leistungen noch starker beeinflussen. In naturnahen Flussabschnitten mit geringen menschlichen Belastungen betragt der Wassertemperaturunterschied zwischen den biozonotischen Zonen im Sommer zwischen 2 °C und 3 °C und ist somit oft ein trennender Faktor zwischen den Zonen. Hohere Wassertemperaturen zwingen die Zonosen zu Anpassungen oder zur Abwanderung in Abschnitte, wo geeignete Habitate vorhanden sind. Ein Anstieg der Wassertemperatur um 2 °C fuhrt daher zu einer Verschiebung der Artenzusammensetzung. Die Ufervegetation ist fur die aquatische Okologie unserer Fliesgewasser wichtig und hat durch die zukunftig zu erwartenden Auswirkungen des Klimawandels auf das thermische Regime eine besondere Bedeutung. Sie kann durch ihre beschattende Wirkung, besonders in Hitzephasen, die Erwarmung der Wassertemperatur um bis 2 °C verringern. Die Synthese unterstreicht, dass fur nachhaltige Flussrevitalisierungen, die Berucksichtigung der gewassertypspezifischen Ufervegetation sowie eine entsprechende aquatische Habitatausstattung unumganglich ist.

The Austrian RADiation monitoring network (ARAD) has been established to advance the national climate monitoring and to support satellite retrieval, atmospheric modeling and the development of solar energy techniques. Measurements cover the downward solar and thermal infrared radiation using instruments according to Baseline Surface Radiation Network (BSRN) standards. A unique feature of ARAD is its vertical dimension of five stations, covering an altitude range between about 200 m a.s.l (Vienna) and 3100 m a.s.l. (BSRN site Sonnblick). The paper outlines the aims and scopes of ARAD, its measurement and calibration standards, methods, strategies and station locations. ARAD network operation uses innovative data processing for quality assurance and quality control, utilizing manual and automated control algorithms. A combined uncertainty estimate for the broadband shortwave radiation fluxes at all five ARAD stations, using the methodology specified by the Guide to the Expression of Uncertainty in Measurement indicates that relative accuracies range from 1.5 to 2.9 % for large signals (global, direct: 1000 W m−2, diffuse: 500 W m−2) and from 1.7 to 23 % (or 0.9 to 11.5 W m−2) for small signals (50 W m−2) (expanded uncertainties corresponding to the 95 % confidence level). If the directional response error of the pyranometers and the temperature response of the instruments and the data acquisition system (DAQ) are corrected, this expanded uncertainty reduces to 1.4 to 2.8 % for large signals and to 1.7 to 5.2 % (or 0.9–2.6 W m−2) for small signals. Thus, for large signals of global and diffuse radiation, BSRN target accuracies are met or nearly met (missed by less than 0.2 percentage points, pps) for 70 % of the ARAD measurements after this correction. For small signals of direct radiation, BSRN targets are achieved at two sites and nearly met (also missed by less than 0.2 pps) at the other sites. For small signals of global and diffuse radiation, targets are achieved at all stations. Additional accuracy gains can be achieved in the future through additional measurements, corrections and a further upgrade of the DAQ. However, to improve the accuracy of measurements of direct solar radiation, improved instrument accuracy is needed. ARAD could serve as a useful example for establishing state-of-the-art radiation monitoring at the national level with a multiple-purpose approach. Instrumentation, guidelines and tools (such as the data quality control) developed within ARAD are intended to increase monitoring capabilities of global radiation and thus designed to allow straightforward adoption in other regions, without high development costs.

The interest in the assessment of performance loss rate (PLR) of Photovoltaic (PV) modules and arrays has been increasing as long as the global installed power expands and ages. Reliable performance metrics, statistical methods and filtering techniques exploiting continuous outdoor measurements are therefore needed, in order to foster solar bankability of PV systems. This work presents an improved estimation method to decrease the uncertainty associated to PLR assessment by (a) using the array generated power metric corrected to Standard Test Conditions (STC), namely P max , STC , to minimize seasonal oscillations, (b) applying a filtering technique to eliminate outliers and (c) performing linear interpolation on P max , STC monthly averages series. Estimated PLR and its uncertainty are assessed using three-years data from twenty-four grid-connected PV arrays representing nine different PV technologies and results are compared with two other widely-recognized performance metrics, namely: the Array Performance Ratio ( PR a ) and the Array Photovoltaic for Utility Systems Applications ( PVUSA a ). Results show (a) that adding spectral correction to irradiance and temperature correction reduces the uncertainty of 25% on average and (b) that the uncertainty associated to P max , STC metric is reduced to more than 60% on average with respect to the other investigated metrics for crystalline silicon-based technologies, while it is comparable in the case of thin-film technologies. Finally, two procedures estimating the first year PLR and the the first five months PLR are presented and discussed.

The effect of contrails on global short-wave radiation (sum of direct and downward diffuse solar radiation) and on solar energy gain was investigated. The study was performed during days with high contrail persistence and focused on situations where the contrails were obstructing the sun. Measurements of cloudiness using a fish-eye camera, diffuse and direct short-wave measurements and measurements of the short circuit current of three different types of photovoltaic (PV) modules were performed at the Kanzelhöhe Observatory (1540 m a.s.l.) with a time resolution of 1 min over a period of 1 year. The results show that contrails moving between sun and observer/sensor may reduce the global radiation by up to 72%. An analysis of contrail persistence and the influence of contrails on global irradiance and solar energy gain is presented. The losses in solar energy gain that were recorded may be critical under specific circumstances.

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 non-heatwave 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 pre-alpine 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.

Riparian vegetation strongly influences the solar radiation input, especially into small- to medium-sized rivers. Solar radiation is one of the main impact factors concerning the river water temperature regime. Effects of different vegetation management strategies on incident solar radiation are to a large extent unknown. In this study, the stream vegetation model Shade-a-lator 6.2 is calibrated using experimental investigations. The Shade-a-lator 6.2 model is adapted for simulations of the influence of willow coppice riparian vegetation on incident solar radiation on rivers since they are characteristic species of riparian plant associations. The main objective is the simulation of riparian vegetation management scenarios based on the calibrated Shade-a-lator 6.2. Results show that plant configuration effectively influences the energy input into the river system. The Shade-a-lator 6.2 is a helpful instrument to take into account different riparian management strategies. Simulations showed that the largest solar radiation reduction occurred for an Austrian (Vienna) west to east orientated river with 10 m width at the time of highest sun elevation when the vegetation was homogeneously distributed along the whole river stretch, starting right next to the river, with a minimum vegetation height of 15 m and a minimum width of 2 m. Based on these conditions, a reduction of approximately 85% of global irradiance was obtained.

Within this study, the erythemal ultraviolet (UV) exposure received by different parts of the body during four different activities is determined. Optoelectronic devices were used to measure the erythemal UV exposure at 10 different positions of the body. The measuring devices were fixed on the forehead, on the shoulders, on the arms, on the chest, on the thighs and on the lower legs. The measurements were performed during the following activities of the test persons: walking, sitting, lying and sitting up. The measurements were performed on four clear sky days in the early afternoon at 1 s interval. One measurement sequence was taking 30-40 min. For the analysis of the measured UV exposures, the ambient UV is taken as a reference to remove the atmospheric fluctuations on the measured UV exposure. The strong dependence of the UV exposure on the activity and on the orientation of the test person is shown. Most of the body parts receive the highest exposure, when the test subject is sitting up or lying. The shoulders are most at risk when the test person is walking, whereas during the activities sitting up and lying the legs are most at risk.

The influence of expected changes in heat wave intensity during the 21st century on the temperatures of an pre-alpine river are simulated and the mitigating effects of riparian vegetation shade on the radiant and turbulent energy fluxes analysed. Minor stream water temperature increases are modelled within the first half of the century, but a more significant increase is predicted for the period 2071–2100. The magnitude of maximum, mean and minimum stream temperature rises for a 20 year return period heat event was estimated to be in the region of 3 °C. Additional riparian vegetation is not able to fully mitigate the expected temperature rise caused by climate change, but can reduce maximum, mean and minimum stream temperatures by 1 to 2° C. Removal of existing vegetation amplifies stream temperature increases. Maximum stream temperatures could increase by more than 4 °C even in yearly heat events.

Radiative transfer models (RTM) are used to calculate spectral and broadband irradiance, given a set of input parameters that are representative of the atmospheric state. While many studies exist on their accuracy, there is still a research gap in the assessment of their uncertainty, due to the nonlinear and not differentiable nature of the Radiative Transfer Equation, which is the core of a RTM. This study evaluates the uncertainty of both spectral and broadband irradiance calculated with the radiative transfer model SDISORT implemented in the tool UVSPEC within the range 280–2500 nm. A set of input values representing the atmospheric state at Kanzelhohe Observatory (Austria) site at 10:00 on April 25th, 2013 is taken as reference and a Monte Carlo technique is used to propagate the uncertainty of input parameters to the model output. Both the effects of single input parameter uncertainty and of their combination are evaluated, as well as the influence of the deviation of input values from the reference set. Results show that ozone column is an important source of uncertainty in the UV-B region, while the uncertainties of Angstrom aerosol turbidity coefficient and extraterrestrial spectrum affect the whole spectral range. Considering a reasonable variability range for all involved input parameters, the overall uncertainty of broadband global horizontal irradiance is between 2.9% and 5.9%. These values are higher, but still comparable, to typical uncertainty values of outdoor-deployed spectroradiometers.

The effects of clouds and surface albedo on spectral UV irradiance are investigated at the mountain observatory Hoher Sonnblick (47.05°N, 12.95°E, 3106 m a.s.l.) in the Central Austrian Alps. Spectral UV radiation in the presence of clouds is measured with a Bentham spectroradiometer along with detailed cloud observations. Ratios of measured to modeled clear sky UV intensities (cloud modification factors) are evaluated for over 9000 spectral UV measurements to quantitatively provide the dependency of cloud modification factors on total cloud amount, cloud type, wavelength, and effective surface albedo. Effective albedo can be altered through changes in snowline height and clouds below the station. Average albedo is increased by 0.28 ± 0.15 due to cloud cover ≥ 4/8 below the observatory, accounting for cloud modification factors in the range of 1.02–1.14 in 75% of the investigated cases. Compared to snow-free conditions, an irradiance enhancement of 1.22 at 305 nm arises from a mean albedo of 0.68 and clear sky conditions, corresponding to a snowline height of 1000 m. Enhancements through augmented albedo can be considerably stronger under the presence of cloudiness. Enhancements through clouds are most commonly found with clouds below the station, accounting for about 40% of all cases of enhancements, often occurring in the presence of cumulus clouds (Cu, Sc, Ac) with an unobstructed solar disk. Analysis of total sky images reveals that enhancements can also be observed when the solar disk is obstructed by clouds or the sky is overcast.

In this study ideas from extreme value theory are for the first time applied in the field of stratospheric ozone research, because statistical analysis showed that previously used concepts assuming a Gaussian distribution (e.g. fixed deviations from mean values) of total ozone data do not adequately address the structure of the extremes. We show that statistical extreme value methods are appropriate to identify ozone extremes and to describe the tails of the Arosa (Switzerland) total ozone time series. In order to accommodate the seasonal cycle in total ozone, a daily moving threshold was determined and used, with tools from extreme value theory, to analyse the frequency of days with extreme low (termed ELOs) and high (termed EHOs) total ozone at Arosa. The analysis shows that the Generalized Pareto Distribution (GPD) provides an appropriate model for the frequency distribution of total ozone above or below a mathematically well-defined threshold, thus providing a statistical description of ELOs and EHOs. The results show an increase in ELOs and a decrease in EHOs during the last decades. The fitted model represents the tails of the total ozone data set with high accuracy over the entire range (including absolute monthly minima and maxima), and enables a precise computation of the frequency distribution of ozone mini-holes (using constant thresholds). Analyzing the tails instead of a small fraction of days below constant thresholds provides deeper insight into the time series properties. Fingerprints of dynamical (e.g. ENSO, NAO) and chemical features (e.g. strong polar vortex ozone loss), and major volcanic eruptions, can be identified in the observed frequency of extreme events throughout the time series. Overall the new approach to analysis of extremes provides more information on time series properties and variability than previous approaches that use only monthly averages and/or mini-holes and mini-highs.

Several UV data products derived from satellite measurements, 1-D and 3-D radiative transfer modeling are compared with high-quality ground-based measurements. Data products include the UV index, erythemally weighted daily dose and spectrally resolved UV irradiances at 305, 310, 324 and 380 nm. The study focuses on the UV radiation climate in mountainous terrain under cloud-free conditions. The results show, that overall the 3-D- and the 1-D-model agree best with the measurements (average ratio 1.10 and 1.13, range 0.88-1.6). It is also found that snow and local topography have a rather minor impact on ground UV-irradiance, while altitude plays a significant role >5 %). Satellite-retrieved values significantly underestimate irradiance for most of our stations due to erroneous cloud correction (average ratio 0.89, range 0.6-1.35). However, if one compares the uncorrected (cloud-free) satellite-retrieved values to the measurements, the ratios are only slightly larger (average ratio 1.14, range 0.8 - 1.6) than for the 1-D- and 3-D-model. The main deficiencies arise in determining the correct surface height and albedo within the satellite-retrieval algorithm.

This work investigates the occurrence frequency of days with high erythemal UV doses at three stations in Switzerland and Austria (Davos, Hoher Sonnblick and Vienna) for the time period 1974-2003. While several earlier studies have reported on increases in erythemal UV dose up to 10% during the last decades, this study focuses on days with high erythema! UV dose, which is defined as a daily dose at least 15% higher than for 1950s clear-sky conditions (which represent preindustrial conditions with respect to anthropogenic chlorine). Furthermore, the influence of low column ozone, clear-sky/partly cloudy conditions and surface albedo on UV irradiance has been analyzed on annual and seasonal basis. The results of this study show that in the Central Alpine Region the number of days with high UV dose increased strongly in the early 1990s. A large fraction of all days with high UV dose occurring in the period 1974-2003 was found especially during the years 1994-2003, namely 40% at Davos, 54% at Hoher Sonnblick and 65% at Vienna. The importance of total ozone, clear-sky/partly cloudy conditions and surface albedo (e.g. in dependence of snow cover) varies strongly among the seasons. However, overall the interplay of low total ozone and clear-sky/partly cloudy conditions led to the largest fraction of days showing high erythemal UV dose. Furthermore, an analysis of the synoptic weather situation showed that days with high erythemal UV dose, low total ozone and high relative sunshine duration occur at all three stations more frequently during situations with low pressure gradients or southerly advection. (C) 2010 Elsevier B.V. All rights reserved.

The potential of hyperspectral imagery for the determination of drought risk zones, responsible for heterogeneous plant growth due to different soil compositions, was assessed at the field scale. The research was carried out in the Marchfeld region, an agricultural, flat area east of Vienna, Austria, during June 2005 by means of an airborne imaging spectrometer (HyMap). The inversion of a radiative transfer model by using a look-up-table (LUT) approach was performed to retrieve canopy parameters, indicators of plant growth, such as leaf area index (LAI), chlorophyll content and a soil reflectance factor (ALFA). To quantify ALFA with respect to its relationship to soil surface water content, the soil reflectance was measured at different levels of known soil water conditions. Finally, a cluster analysis was performed using the parameters estimated from the model inversion to explain plant growth variability, quantified by means of measured yield. The results were compared with a simple Normalized Differenced Vegetation Index (NDVI) approach to evaluate the contribution of hyperspectral data to vegetation monitoring. Areas characterizing different levels of drought risk could be determined by both methods with a similar performance.

The homogeneous canopy reflectance model ACRM was used to simulate forest reflectance and was compared with hyperspectral data of the topographically complex experimental forest Rosalia of the University of Applied Life Sciences and Natural Resources (BOKU) in Austria. Forward and inverse modes of the ACRM model were validated. Ground truth data were taken (1) from experiments performed at 17 pure beech plots and (2) from model simulations performed for 21 pure beech plots using an ecosystem model. The validations were performed separately for these two types of reference data. The ground reflectance obtained from the HyMap data was compared with simulations performed with ACRM. In addition to the correction of the data to remove the atmospheric effects, corrections had to be applied to remove the effects of the complex topography of the area of Rosalia. The simulated reflectance showed an offset to the HyMap retrieved reflectance between +4% and +6% in the visible (extending from 400 nm to 700 nm), +28% to +30% in the near infrared (NIR) (extending from 700 nm to 1400 nm) +53% to +77% in the middle-infrared (MIR) (extending from 1400 nm to 3000 nm) using the modelled and the experimental ground truth, respectively. The correlation coefficient varied between 0.35 and 0.45 in the visible, 0.6 and 0.76 in the NIR and between 0.37 and 0.64 in the MIR. This correlation may be improved, if within canopy fluctuations of chlorophyll and water content were available. The leaf area index (LAI) was retrieved using the ACRM model. The estimated LAI was in good agreement with the LAI ground measurements and systematically higher by 0.1 compared to the simulated LAI. The correlation was 0.49 and 0.82, respectively. Altogether, the ACRM model showed a large offset to the HyMap retrieved reflectance in the NIR and MIR wavelength ranges. A precision around 33% to 74% may be expected after correction of the offset. The LAI may be determined with a precision between 0.32 and 0.5. The ACRM model is a useful tool to predict LAI. Care should be taken for the forward modelling of forest canopy reflectance.

Because of its biological effects, erythemal ultraviolet (UV-ERY) radiation (280-400 nm) is a significant part of solar radiation spectrum. In this study a statistical model for estimating daily UV-ERY radiation values was developed. It is based on ground measurements conducted at eight Austrian stations (from 2000 to 2002). As inputs the model requires daily global radiation, daily extraterrestrial radiation, information about the column of total ozone in the atmosphere and the altitude of a selected station. Subsequently the performance of the model was verified by an independent data set originating from measurements in Austria and Czech Republic stations. The verification showed satisfactory performance of the model: the coefficient of determination (R 2 ) varied from 0.97 to 0.99, the root mean square error (RMSE) varied from 9.3 % to 17.7 % and the mean bias error (MBE) varied from -2.5 % to 2.0 %. In addition, the results of the model at Hradec Kralove station were compared with equivalent UV-ERY data from the Solar Radiation Database (SoDa), which are available on the Internet. After successful verification, the model was implemented within the ArcInfo GIS framework in order to carry out a spatial assessment of a stratospheric ozone reduction episode. The event of July 2005 in the Czech Republic was used as a case study. On 30 July 2005 the total ozone amount dropped 12.5 % below the long-term mean, which led to UV-ERY radiation increment ranging from 214 to 391 J·m -2 ·day -1 .

Because sinkholes are an excellent natural laboratory for studying processes leading to the formation, maintenance, and dissipation of temperature inversions, an extended set of meteorological field experiments was conducted in limestone sinkholes of various sizes and shapes in the eastern Alps during the period from 17 October 2001 through 4 June 2002. The experiments were conducted in an area surrounding the Gruenloch Sinkhole, which in earlier years had recorded the lowest surface minimum temperature in Central Europe, −52.6°C. A dense array of surface temperature sensors and three automatic weather stations were operated continuously during the experimental period, and special experiments enhanced with tethersondes and other equipment were conducted from 2 to 4 June 2002. An overview of the experiments is presented and first results are given.

In this study the sensitivity of the erythemally effective radiation to uncertainties in operationally measured total ozone content of the atmosphere (TOC) was estimated. For this, daily operational TOC measurements from different instruments were applied covering the period from 1997 to 1999. Measurements were gained from space by Earth Probe Satellite, Earth Remote Sensing satellite/Global Ozone Monitoring Experiment and Operational Vertical Sounder and from the ground by Dobson and Brewer spectrophotometers for the locations of Hradec Kralove (Czech Republic, 50 degrees N), Nairobi (Kenya, 1 degrees S) and Springbok (Republic of South Africa, 30 degrees S). The values were used as input parameter to model calculations of erythemally effective irradiance and daily radiant exposure. The differences due to the use of TOC from different sources were analyzed with respect to the Ultraviolet Index (UVI). The UVI was introduced as a tool for sun protection and health care. Therefore, it is of special importance to know the restriction of accuracy. As a tool of health care, the maximum uncertainties are of interest and are described in using the 95%-percentile and the maximum differences. This study shows that differences, i.e. uncertainties (95%-percentile) are in the order of 1 UVI. Independently on the location, however, extreme differences may overstep 3 UVI. For the daily dose the 95%-percentile is around 7.5 UVI hours (UVIh) but differences higher than 20 UVIh were also found.