No abstract

In the past few decades, severe heat waves were representative of the weather conditions in various parts of the world. They had distinctly negative impacts on humans, plants, animals and different economic sectors. Particularly in cities, where most humans are living, their well‐being, efficiency and health were affected, which even caused a relatively high mortality rate. This is why a large interest still exists to analyse heat waves in the past by use of statistical methods. As an investigation on heat waves is not available for the territory of Ukraine up to now, a retrospective analysis was conducted. Its main aims were (1) to determine the frequency of heat wave episodes for this country and (2) to analyse their spatiotemporal distribution, duration and intensity. On the basis of 13 selected stations of the meteorological network of the Ukrainian Hydrometeorological Centre, daily values of maximum air temperature (Ta,max) in the summer months June to August were used to determine heat wave episodes according to the definition recommended by the IPCC. For all stations, complete and reliable Ta,max time series were available for the period 1951–2011. With respect to some stations, the Ta,max time series already started some years earlier, e.g. in 1936 for five stations and even in 1911 for four stations. However, the Ta,max time series of almost all stations had gaps in the summer months before 1951, particularly in the 1940s of the 20th century. As they could not be filled in a satisfying way, this limitation was considered in the data analysis. The results indicate that most of the heat wave episodes occurred at stations located in Eastern Ukraine. In contrast to other decades, the number of heat wave episodes was highest for almost all stations in the decade 2001–2010. The fewest heat wave episodes were determined for the two decades 1961 to 1980. The longest heat wave duration varied between 7 d in Henichesk (southern seashore) and 24 d in Lugansk (Eastern Ukraine). For many stations, the longest heat wave duration occurred in the first two decades of August 2010, i.e. in the period of the extremely severe heat wave in Western Russia. The intensity of heat waves was analysed by use of the cumulative Ta,max excess. The results show that heat waves of the longest duration mostly represented the strongest heat waves. The 24‐d heat wave 2010 in Lugansk was the strongest in the investigation period quantified by a cumulative Ta,max excess of 128 °C.

Increasing heat will be a significant problem for Central European cities in the future. Shading devices are discussed as a method to mitigate heat stress on citizens. To analyze the physical processes, which are characteristic of shading in terms of urban human-biometeorology, experimental investigations on the thermal effects of shading by a building and shading by tree canopies were conducted in Freiburg (Southwest Germany) during typical Central European summer weather. Urban human-biometeorology stands for the variables air temperatureTa, mean radiant temperatureTmrt, and physiologically equivalent temperature PET, that is the human-biometeorological concept to assess the thermal environment which was applied. The measuring setup consists of specific human-biometeorological stations, which enable the direct or indirect determination ofTa,Tmrt, and PET. With respect to both shading devices, theTareduction did not exceed 2°C, while PET as a measure for human heat stress was lowered by two thermal sensation steps according to the ASHRAE scale. AsTmrthas the role of a key variable for outdoor thermal comfort during Central European summer weather, all radiant flux densities relevant to the determination ofTmrtwere directly measured and analyzed in detail. The results show the crucial significance of the horizontal radiant flux densities forTmrtand consequently PET.

No abstract

The RayMan software is worldwide applied in investigations on different issues in human-biometeorology. However, only the simulated mean radiant temperature (T ) has been validated so far in a few case studies. They are based on T values, which were experimentally determined in urban environments by use of a globe thermometer or applying the six-directional method. This study analyses previous T validations in a comparative manner. Their results are extended by a recent validation of T in an urban micro-environment in Freiburg (southwest Germany), which can be regarded as relatively heterogeneous due to different shading intensities by tree crowns. In addition, a validation of the physiologically equivalent temperature (PET) simulated by RayMan is conducted for the first time. The validations are based on experimentally determined T and PET values, which were calculated from measured meteorological variables in the daytime of a clear-sky summer day. In total, the validation results show that RayMan is capable of simulating T satisfactorily under relatively homogeneous site conditions. However, the inaccuracy of simulated T is increasing with lower sun elevation and growing heterogeneity of the simulation site. As T represents the meteorological variable that mostly governs PET in the daytime of clear-sky summer days, the accuracy of simulated T is mainly responsible for the accuracy of simulated PET. The T validations result in some recommendations, which concern an update of physical principles applied in the RayMan software to simulate the short- and long-wave radiant flux densities, especially from vertical building walls and tree crowns.