Address by the President of the Republic of Uzbekistan Shavkat Mirziyoyev to Oliy Majlis on January 24, 2020, emphasizes that "... we should turn the tourism industry into a strategic sector of the economy." In order to address the task, the President of the Republic of Uzbekistan Shavkat Mirziyoyev held a meeting on tourism development, further popularization of physical education and sports affairs on January 28, 2020. It was noted at the meeting, that 6.7 million tourists visited Uzbekistan in 2019. The State Committee for Tourism Development of the Republic of Uzbekistan was tasked with increasing the foreign tourists’ traffic upto 7.5 million in 2020, and upto 10 million in 2022 and upto 12 million in 2025.

Uzbekistan objectively has all prerequisites for the intensive development of domestic and foreign tourism: features of its geographical position and topography, favorable climate, rich natural, historical, cultural and tourist-recreational potential. Acquaintance with the listed tourist potential usually takes place within natural and climatic conditions. In this case, the weather has a great impact on the physiological state of a person. First of all, it is its thermal comfort, which is a condition when as much heat is removed from a person as his body produces. Figuratively speaking, a person does not feel either cold or overheating.

To date, the number of works devoted to studies of bioclimatic conditions is insignificant. They are mainly carried out in some CIS countries (Garabatyrov, 2004; Andreev, 2011; Perevedentsev and Shumikhina, 2016). These studies give an evaluation of the bioclimatic conditions of various territories based on the analysis of a large number of biometeorological indices applied to tourism, medicine, urban planning, etc. In foreign countries, such studies are carried out by scientists from different countries of the world (Höppe, 1999; Matzarakis, 2014(a), 2014(b); Daneshvar et al., 2013; Çalişkan et al., 2013; Lin and Matzarakis, 2008; Akinbobola et al., 2017). The studies are based on the use of Physiological Equivalent Temperature (PET) proposed by P.R. Höppe (1999). The above studies assessed the bioclimatic conditions of several European countries, such as Greece and the countries of the Balkan Peninsula, Taiwan and Nigeria for tourism purposes. This method is especially extensively used in Iran and Turkey. In connection with the Olympic Games in Tokyo in 2020, the method was also applied to the conditions of Japan (Matzarakis, 2019).

In Uzbekistan a number of studies, carried out in the 60-80s of the last century under the guidance of B.A. Aizenstat (Aizenstat, 1973; Aizenstat and Lukina, 1982) are known. In the works, on the basis of classical biometeorological indices, bioclimatic conditions not only in some cities of Uzbekistan, but throughout the territory of Central Asia were studied. Taking into account ongoing global climate change and new available evaluation methods, there is currently an objective necessity to study the bioclimatic conditions of various territories of Uzbekistan.

The data of standard observations of air temperature and dew point at Samarkand (vn.m. - 666.0 m), Dagbit (vn.m. - 645.1 m), Tashkent-Observatory (vn.m. - 467.7 m) and Chimgan (vn.m. - 1670.0 m) meteorological stations for the period 2009-2018 was served as an information basis for the study. The evaluation of thermal comfort conditions is carried out on the base of the thermohygrometric coefficient of air aridity (K), which reflects the simultaneous influence of temperature and air humidity (Petrov and Abdullaev, 2010):

where Т is the air temperature in Kelvin, t_d is the dew point temperature, Δ is the dew point temperature deficit.

Being a dimensionless quantity, the coefficient shows how the water vapor far from the saturation state under its given content and under a given air temperature. In this case, an increase in temperature in the case of constant moisture content leads to an increase in air aridity. An increase in moisture content in the case of constant air temperature, in contrast, reduces aridity. It is completely obvious that the value of this quantity depends on many weather factors: amount and type of precipitation, state and type of underlying surface, amount and shape of clouds, etc. Based on the dependence of person’s thermal sensations on temperature and aridity coefficient, 6 zones of these sensations have been identified: 1 - very cold, 2 - cold, 3 - comfort, 4 - relative comfort, 5 - hot, 6 - very hot (Petrov and Akhmedova, 2019).

The annual distributions of long-term average thermal comfort conditions are obtained for all eight observation periods. As an example, nomograms of the distribution of thermal comfort conditions in the studied settlements for 11 a.m., 2 p.m. and 5 p.m local time are given (Fig. 1, 2).

An analysis of the results shows that at all points the bioclimatic conditions have a pronounced annual course. From the second half of October to the first half of April at all observation times in Samarkand, Dagbit and Tashkent, i.e. on the flat territory discomfort conditions “very cold” and “cold” are registered. During daytime observation periods, the thermal comfort zone includes periods from the second half of September to the first half of October and from April to the first half of May. In the remaining periods of the year (late spring - early autumn), according to long-term average evaluation, the conditions of zone 5 and 6 - “hot” and “very hot” —are practically not observed (Figs. 1, 2a).

Analysis of the literature references shows that the applied in the CIS countries methods for assessing bioclimatic conditions are based on a large set of biometeorological indices (Andreev, 2011). The authors cite more than 30 names of biometeorological indices. These indices are divided into seven groups: 1 - temperature and humidity indicators; 2 - temperature-wind (cold stress indices); 3 - temperature-humidity-wind (for shady areas); 4 - temperature-humidity-wind (taking into account solar radiation); 5 - indices of pathogenicity and climate variability; 6 - climate continental indices; 7 - indices characterizing the state of the atmosphere. Emphasizing a great scientific value of these studies results, it should be underlined that the information provided cannot be easily understood. In order to interpret the information, end user, in our case, a tourist, should possess certain knowledge in the field of biometeorology. The above make difficult to apply it for the tourism industry. Study results based on usage of Physiologically Equivalent Temperature (PET) are simple, informative, and understandable to everyone (Matzarakis, 2014(a), 2014(b); Daneshvar et al., 2013; Çalişkan et al., 2013; Lin and Matzarakis, 2008; Akinbobola et all, 2017). However, being a temperature-humidity index, PET only indirectly takes into account the effect of air humidity on thermal comfort. For example, in Europe, thermal comfort conditions are in the range of 18–23°C (Höppe, 1999; Matzarakis et al., 2014(a)). For Taiwan, this range is 26-30°C (Lin and Matzarakis, 2008), and in Nigeria it is 24-27°C (Akinbobola et al., 2017). According to estimates made on the basis of the thermohygrometric coefficient of air aridity, the conditions of thermal comfort can be observed even at sufficiently low temperatures (10-12°C), when the air contains high moisture. Our proposed methodology for assessing thermal comfort for a particular area based on the thermohygrometric coefficient of air aridity can be applied to any climatic conditions. Unlike foreign analogues, К makes it possible in a relatively simple way to simultaneously take into account the influence of temperature and air humidity on the conditions of thermal comfort of the human body. Thus, it is an objective characteristic of the weather and climate of the study area.

Based on the analysis of the obtained results, it is shown that the most favorable months in terms of thermal comfort conditions are April, May, September and October for the arrangement of tourist events in the flat-piedmont areas.

The revealed tendencies of annual and daily course of the coefficient, calculated long-term average monthly and daily characteristics of repeatability of thermal comfort conditions can be applied for organizing of tourist events.