**3. Results**

Regional climate change leads to a number of changes in the atmosphere and the sea, which potentially can be both positive and negative to socio-economic development. The most known consequence of climate change is warming, but this is not a single effect. Climate change is accompanied by changes in atmospheric circulation, the position of atmospheric fronts, trajectories of cyclones and anticyclones, atmospheric pressure, wind speed and direction, precipitation intensity and location, intensification of extreme weather events, and other processes and phenomena. In the sub-sections below, we try to describe the major natural features which are observed regularly during the past two decades at the Russian coast of the Black Sea, and we focus especially on the negative ones in relation to coastal tourism.

### *3.1. Warming of the Region and Extreme Events*

Warming of the air and the sea is an evident consequence of global and regional climate change in the Black Sea Region. Ginzburg et al. [35] showed that the air temperature in the Black Sea Region is rising with a rate of +0.053 ◦C/year for 1980–2020, which is three times faster than for the 1935–2017 time period. The highest rate of change of +0.06 ◦C/year is located along the coastal zone of the northeastern Black Sea. Since the late 1990s, the maximum monthly mean values of the near-surface air temperature during summer on average increased considerably, with an extreme value of 27.2 ◦C in 2010, when a blocking anticyclone stood over the central part of European Russia for 55 days since the end of June [36]. The above-mentioned analysis, as well as previous publications on regional climate change in the Black Sea Region mentioned in the review [37], showed air temperature trends for all 12 months of the year during a certain time period. In the present study, we are interested in what is happening during summertime, which is a tourist season. This is why we calculated the interannual variability of the air temperature for the summer season (June, July, August) for a 40 years-long time period from 1981–2020 (Figure 2).

**Figure 2.** Interannual variability of the near-surface air temperature over the northeastern Black Sea during summer from 1981–2020 based on the MERRA-2 M2IMNXASM\_5.12.4 Model.

> Figure 2 confirms that, on average, the air temperature during summer has been progressively warming over the past 40 years from around 21 ◦C in the early 1980s to around 24 ◦C in the 2010s. The transition between the period of a slight increase in the air temperature to a more stable period occurred between 2004 (21.3 ◦C) and 2012 (24.2 ◦C). The hottest summer, 25.5 ◦C, was registered in 2010 due to a long-standing blocking of an anticyclone over the central part of European Russia. Year-to-year variability of the air temperature varied from 0.5 to 2.5 ◦C from 1981 to 2011, but since 2012 the air temperature variability has become more stable and has not exceeded 1 ◦C.

> These data show that the air temperature, on average, gets warmer. The air temperature is becoming more comfortable for coastal tourism for a longer period of time, and the tourist season slowly expands for May and September. The same analysis for

May (Figure 3) showed that the air temperature rose from around 15 ◦C at the end of the 20th century to 16 ◦C in the first decade of the 21st century, and 17 ◦C in the 2010s. First, the average air temperature increase in May is lower than the same parameter for the average value for the summertime. Second, 17 ◦C does not seem to be comfortable for opening the tourist season. Third, the weather in May is very unstable, because from year to year the air temperature has varied from 15 to 19 ◦C over the past 10 years. Thus, it is evident that during the coming decades, May will not be a month from which the tourist season will start. At the same time, September shows to be a better candidate for expansion of the summer season because its average air temperature is 3–4 ◦C higher than in May, and it is already comparable with June (Figure 4). Since 2005, its average temperature almost yearly has been over 20 ◦C, which can be regarded as a psychological mark for summertime, and in 2015, 2017, and 2020 it was over 22 ◦C.

Global and regional warming is accompanied by extreme weather events such as heat and cold waves, draughts and frosts, heavy rains and snowfalls, etc. This effect is also observed in the eastern part of the Black Sea which was especially investigated for the period 1950–2015 based on daily air temperature data [38]. Kostianoy et al. [38] showed an increase in the amplitude of air temperature extremes with positive anomalies from 3.6 ◦C to 3.9 ◦C for phenomena exceeding one standard deviation (1 SD), and from 5.5 ◦C to 6 ◦C for phenomena exceeding 2 SD. At the same time, the amplitude of extreme events with negative anomalies remained practically unchanged: 3.9 ◦C and 7.2 ◦C, respectively. The number of extreme events with positive anomalies exceeding 1 SD increased from 10–14 to 28–32 events per year, and exceeding 2 SD—from 1–2 to 12–14 events per year. At the same time, the number of extreme events with negative anomalies exceeding 1 SD decreased from 22–24 to 8–10 events per year, and exceeding 2 SD—from 5–6 to 2–3 events per year. The average duration of extreme events with positive anomalies exceeding 1 SD increased from 2.5 to 3.5 days, but with negative anomalies, practically remained unchanged—3 days. The duration of extreme events with anomalies exceeding 2 SD increased from 1 to 2 days for positive anomalies events and remained the same (2 days) for negative anomalies [38].

**Figure 3.** Interannual variability of the near-surface air temperature over the northeastern Black Sea in May from 1981–2020 based on the MERRA-2 M2IMNXASM\_5.12.4 Model.

**Figure 4.** Interannual variability of the near-surface air temperature over the northeastern Black Sea in September from 1981–2020 based on the MERRA-2 M2IMNXASM\_5.12.4 Model.

It means that, on average, heat waves in the Eastern Black Sea became a bit stronger, their frequency doubled for anomalous events exceeding 1 SD and reached 28–32 events per year, while strong events exceeding 2 SD increased 10 times from 1–2 to 12–14 per year, and the duration of both types of extreme events increased as well.
