The aim of this study is assessment of thermal comfort conditions during heat waves in Ukraine in the years 1961-2015. The assessment is based on the thermal index Physiologically Equivalent Temperature. This study uses data from 29 meteorological stations across Ukraine. The research showed an increasing frequency of occurrence of heat waves (HWs) in the territory of Ukraine in the last decades. East and south Ukraine (except of coastal stations) experienced the most strenuous human-biometeorological conditions whilst HWs were recorded in the country. Lower mean PET values were found in Western region of the country. The obtained results suggest that the HW event of 2010 was the longest and the most strenuous HW in human-biometeorological terms since 1961.
Formulation of the problem. Studies of bioclimate of a territory are aimed at determining the favorable and adverse impacts of various climatic factors and their combinations on the human body. Complex urban morphology has a significant impact on microclimate and, accordingly, on thermal comfort of a person in such an environment. The height of buildings, street orientation, and distance between buildings alter the solar energy inlet, affect thermal regime, transform the wind speed and direction at the street level. Studies of the bioclimatic conditions of urban areas during the warm season are highly relevant as they provide an opportunity to evaluate human thermal sensations in the city, as well as the potential effectiveness of adaptation measures to heat stress (architectural measures and measures based on the use of green areas and water bodies). The purpose of the article. The aim of this research is to simulate the bioclimate of an urban environment to determine the human thermal load in summer months based on modern bioclimatic indices and software. Methods. For the purpose of this study, a part of the territory of the Osokorky residential area of Kyiv was selected. To get values of the main meteorological parameters of the researched area, a three-dimensional, prognostic, microscale model ENVI-met was used. ENVI-met pertains to the CFD-models (computation fluid dynamics model) and is designed for microscales with a horizontal resolution from 0.5 to 10 m and with a time step of 10 seconds as maximum. The PET calculation was performed using the RayMan model. Results. A clear hot summer day (04 August 2017) was chosen for the simulation. The simulation was performed from 6:00 EEST on 4 August till 6:00 EEST the next day (output interval – 1 hour). The simulation results show that the values of the main meteorological parameters (air temperature and humidity, wind characteristics) and physiologically equivalent temperature differ significantly within urban spaces, even across small areas. The amplitudes of PET value were maximum in the daytime and made 12°–15°C. The decrease in the amplitude of the air temperature within the researched area in the evening and night hours led to a notable decrease in the PET amplitude to 2°–3°C. The analysis of the simulated PET values for the researched area confirmed that the residents of the urban areas experience the most intense heat stress while staying in the open asphalted areas during the daytime. The duration of the period with comfortable conditions during the researched day was very short – from 22:00 EEST through midnight. The range of the daily course of PET values at different points of the researched area varied from 19.4° (at point No. 7) to 37.1°C (at point No. 5 located in the well courtyard). Based on the PET values simulated for the researched area and for CAWS Kyiv was found the significant differences between thermal comfort conditions within the complex urban spaces and at the weather station. Therefore, the values of bioclimatic indices simulated based on the weather station data can not be applied with any approximation to solve scientific and applied tasks that require information on the bioclimate at particular points in the urbanized environment. To solve such tasks, it is recommended to apply modern methods – ENVI-met and RayMan models. Scientific novelty and practical significance. For the first time in Ukraine, microclimate and thermal comfort conditions within the complex urban environment has been simulated using ENVI-met and RayMan models. The results of such simulation can be used to choose heat adaptation measures which would help to increase the comfort of the urban areas. The simulation of microclimate and thermal comfort conditions of some parts of the city territory is important stage of design of the buildings, in order to choose the optimal location for buildings and trees and to create the most comfortable conditions for people.
Studying the microclimate of cities is one of the areas of urban meteorology, which are actively developing recently. The research of microclimate and its dependence on building parameters is important not only for scientists but also for architects, engineers and urban planners. Because they can help make the urban environment more comfortable for living and minimize the negative impact of Urban Heat Island, which is especially important in the context of rapid urbanization and in the face of climate change, that is most often reflected in air temperatures increasing. For modern urbanmeteorological studies traditional methods (observation method and statistical methods) cannot remain basic, so they are replaced by numerical simulation tools. One of those tools is the Computational Fluid Dynamics (CFD), which are based on the use of numerical methods to simulate the interaction between the atmosphere and the urban surface. Such approaches are gaining in popularity because of such advantages as accurate modeling of urban geometry and the high-resolution description of airflow in it; the ability to simulate the microclimate in different conditions (weather, buildings, vegetation, water bodies, etc.); numerical simulation can provide information about any researched variable in the entire simulated area. This article describes the modern ENVI-met microclimate model as one of the most common numerical simulation tools. The model is based on the fundamental laws of fluid dynamics and thermodynamics and is able to reproduce the basic processes of interaction between the atmosphere, soil, vegetation and buildings. The model can be used to simulate microclimate conditions, bioclimatology, urban air pollution, and to identify optimal measures for urban adaptation to climate change. The paper provides an overview of studies published in peer-reviewed international journals (in the period from 1999 to the end of 2018) using the ENVI-met model, and also presents its main advantages and disadvantages. The simulation accuracy of the ENVI-met model is analyzed by comparing the simulated data with the measured one.
According to the WUDAPT protocol which is based on the concept of local climate (LCZ) zones T. Oke and I. Stewart the territory of Kyiv was analyzed and was highlighted by the LСZ in the administrative boundaries of the city and within the built-up area (BUA). A map of the local climate zones of the city has been created. The existence of significant differences in the ratio between LCZs within the administrative boundaries of the city and within the BUA is disclosed. It is shown that the areas of LСZ with built-up territories (LСZ-1 – LСZ-9) cover about 40% within the administrative boundaries of Kyiv and over 65 % in BUA, and green areas (LСZ-A, B, C, and D) and water bodies (LСZ-G) cover 32,6 % within the BUA, which is almost twice less than within the administrative boundaries of the city (59,0 %). The LCZ-A are characterized by the biggest differences (dense trees) – within the administrative boundaries of Kyiv it accounts for 32,6 % of the territory, and within the BUA it accounts only 6,7 %. Thus, it is shown that within the territories where the citizens live and work (BUA) about 2/3 of the area is built-up areas with man-made surfaces which are characterized by a much lower albedo (compared to natural) and low water permeability, and accordingly, they are favorable for the formation of microclimatic features. The obtained results are very important for the study of microclimatic conditions and climate of Kyiv, assessment of the thermal comfort conditions of the urban environment, development of measures of adaptation the city to heat, and for solving a number of other practical problems.
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