Extreme heat events are natural hazards affecting many regions of the world. This study uses an example of the six largest cities in Austria to demonstrate the potential of urban climate model simulations applied in prediction mode providing detailed information on thermal conditions. For this purpose, the urban climate model MUKLIMO_3 of the German Meteorological Service (DWD) coupled with the hydrostatic numerical weather prediction model, ALARO, is used to simulate the development of the urban heat island (UHI) in Austrian cities for the summer period of 2019 with a horizontal resolution of 100 m. In addition to the evaluation of UHI predicting skills, other relevant variables, such as humidity and wind characteristics on hourly basis, are also analysed in this paper. Model evaluation confirmed that the MUKLIMO_3 microscale model had the capacity to simulate the main thermal spatiotemporal patterns in urban areas; however, a strong dependence on the input data from the mesoscale model was found. Our results showed large benefit in prediction of maximum air temperatures in urban areas, while the relative humidity predictions of MUKLIMO_3 appear to be much less plausible and show large variety of model prediction skills. Urban climate model simulations using real atmospheric conditions can facilitate better quantification and understanding of day-to-day intra-urban variations in microclimate as well as provide a basis for evaluation of the microclimate prediction skills of mesoscale numerical models with urban extensions.

This article examines the positioning features of polycrystalline, monocrystalline, and amorphous silicon modules relative to the focus points of concentrator photovoltaic modules under real meteorological conditions using a dual tracking system. The performance of the photovoltaic modules mounted on a dual-axis tracking system was regarded as a function of module orientation where the modules were moved step by step up to a point where their inclination differed by 30° compared to the ideal focus point position of the reference concentrator photovoltaic module. The inclination difference relative to the ideal focus point position was determined by the perfect perpendicularity to the rays of the sun. Technology-specific results show the accuracy of a sun tracking photovoltaic system that is required to keep the loss in power yield below a defined level. The loss in power yield, determined as a function of the measurement results, also showed that the performance insensitivity thresholds of the monocrystalline, polycrystalline, and amorphous silicon modules depended on the direction of the alignment changes. The performance deviations showed clear azimuth dependence. Changing the tilt of the modules towards north and south showed little changes in results, but inclination changes towards northwest, southwest, southeast, and northeast produced results diverging more markedly from each other. These results may make the planning of solar tracking sensor investments easier and help with the estimate calculations of the total investment and operational costs and their return concerning monocrystalline, polycrystalline, and amorphous silicon photovoltaic systems. The results also provide guidance for the tracking error values of the solar tracking sensor.

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 (T_can), 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 T_can, 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 T_can (by up to − 1.65°C) for the latter case, indicating the potential of partially reducing/mitigating urban heat island effects.