Climatic and bioclimatic conditions at high-altitude meteorological stations in the Carpathian Mountains and the Sudetes in years 2005-2022

Abstract

The subject of the analysis were the climatic and bioclimatic conditions of the mountainous areas in Central Europe from 2005 to 2022. The study was conducted based on meteorological data from 4 stations located in 2 mountain ranges in Central Europe, which were obtained from the Ogimet database. The analysis examined the course of mean air temperature, winter days, precipitation, snow cover, wind speed, horizontal visibility, as well as the number of days with thunderstorms and fog. Subsequently, bioclimatic indices were analyzed based on the wind chill index (WCI) and the climate severity index by Osokin (So). The results confirm an increase in mean air temperature and a decrease in the number of winter days. The most significant change in mean annual air temperature was recorded at the Carphatian stations: Varful Omu (0.59 °C/10 years) and Łomnica (0.49 °C/10 years). The largest change in the WCI value was recorded at the Carpathian station Varful Omu (51 W/m 2 /10 years), while the So index was 1.4/10 years.

Full text

DOI:10.28974/idojaras.2024.3.2
309
IDŐJÁRÁS
Quarterly Journal of the HungaroMet Hungarian Meteorological Service
Vol. 128, No. 3, July – September, 2024, pp. 309–325
Climatic and bioclimatic conditions at high-altitude
meteorological stations in the Carpathian Mountains and
the Sudetes in years 2005–2022
Filip Miś
Adam Mickiewicz University
Doctoral School of Natural Sciences
Department of Meteorology and Climatology
Bogumiła Krygowskiego 10,
61-680 Poznań, Poland
*Author E-mail: filmis@amu.edu.pl
(Manuscript received in final form October 5, 2023)
Abstract— The subject of the analysis were the climatic and bioclimatic conditions of the
mountainous areas in Central Europe from 2005 to 2022. The study was conducted based
on meteorological data from 4 stations located in 2 mountain ranges in Central Europe,
which were obtained from the Ogimet database. The analysis examined the course of mean
air temperature, winter days, precipitation, snow cover, wind speed, horizontal visibility,
as well as the number of days with thunderstorms and fog. Subsequently, bioclimatic
indices were analyzed based on the wind chill index (WCI) and the climate severity index
by Osokin (So). The results confirm an increase in mean air temperature and a decrease in
the number of winter days. The most significant change in mean annual air temperature
was recorded at the Carphatian stations: Varful Omu (0.59 °C/10 years) and Łomnica
(0.49 °C/10 years). The largest change in the WCI value was recorded at the Carpathian
station Varful Omu (51 W/m2/10 years), while the So index was 1.4/10 years.
Key-words: bioclimate, mountain areas, Europe, climate changes
1. Introduction
Contemporary climate changes, characterized by a significant increase in air
temperatures resulting from human activities, no doubts are raised (IPCC, 2021).
These changes are observed both on global and regional scales. Mountainous
areas are particularly sensitive ecosystems in the context of climate change. Many

310
scientists (Giorgi et al., 1997; Westerling et al., 2006) believe that the alterations
occurring in mountain ecosystems can serve as early warning systems for
recognizing future changes in lowland environments. Climate changes in
mountainous regions have been the subject of numerous studies (Beniston, 2006;
Żmudzka, 2009; Negi and Mukherjee, 2020). In his work, Beniston (2006)
demonstrated a rising trend in air temperatures at selected alpine meteorological
stations. The most significant increase in the analyzed stations was observed in
the 1990s, especially at the high-altitude Saentis station. Żmudzka (2009) showed
an increase in the average air temperature and a rise in the number of hot days,
along with a decrease in the number of cold days in the Polish Tatra Mountains
between 1966 and 2006. Negi and Mukherjee (2020), in their study on the impact
of climate change on Himalayan mountain ecosystems, confirmed an increase in
the average air temperature, resulting in an extended growing season at the foot
of the mountainous region. The subject of climate change in mountainous areas
has also been addressed by Głowicki (2008). In his work on extreme thermal
phenomena in the Sudetes, the author conducted a detailed analysis of extreme air
temperature values at four selected Sudeten meteorological stations. The results
showed an increase in air temperature in almost all months of the year. The highest
changes in maximum air temperature occurred in May (0.6 °C/10 years).
Additionally, the author demonstrated a decrease in the number of frosty and very
frosty days, along with an increase in the number of hot and very hot days. It is a
fact that mountainous areas are characterized by a harsh, challenging climate that
impacts human comfort and well-being.
The scientific discipline concerned with the impact of weather and climatic
conditions on living organisms, including humans, is known as bioclimatology. The
primary goal of bioclimatic research is to determine the direct influence of
atmospheric factors on living organisms and to assess living conditions from a
climate perspective (Kozłowska-Szczęsna et al., 2004). This field of study is gaining
increasing interest among researchers. A very popular focus of bioclimatic studies is
the identification of conditions leading to heat stress in living organisms. To achieve
this, researchers employ various bioclimatic indices to assess the degree of thermal
discomfort experienced by humans. One such index is the Humidex, which was
applied in the study by Charalampopoulos et al. (2006). It gauges the perceived heat
by considering the combined effects of fundamental elements such as temperature
and humidity. Another commonly used index in bioclimatic research is the UTCI
(universal thermal climate index). It evaluates human thermal loads by taking into
account several meteorological parameters, including wind speed, humidity, and
solar radiation. The UTCI index has been employed in numerous bioclimatic studies,
including those by Błażejczyk et al. (2021) and Miszuk (2021). In colder regions, the
wind chill index (WCI) is often utilized, which incorporates wind speed and air
temperature values. This index was adopted in the research conducted by Coronato
(1993), Przybylak and Araźny (2005), and Dogan et al. (2020). In the work of
Przybylak and Araźny (2005) concerning bioclimatic conditions on the Svalbard

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archipelago, conditions at three meteorological stations were compared. The most
severe conditions in terms of the WCI index were observed at the northernmost
station, Ny-Alesund, where the average annual value was 1028 W/m2, whereas at
Svalbard Lufthavn, it was 937 W/m2, and at the Hornsund station, it was 942 W/m2.
When analyzed by months, the most severe conditions were recorded in January,
while the mildest conditions were in July.
The objective of this study was to characterize and assess the climatic and
bioclimatic conditions at high-altitude meteorological stations in Central Europe,
specifically in the Sudetes and the Carpathian Mountains. Additionally, the study
aimed to determine the direction and rate of climatic changes over the investigated
multi-year period.
2. Study area, source material, and study methods
The analysis utilized data from four high-altitude meteorological stations located
in two mountain ranges in Central Europe (Fig. 1, Table 1). These stations are
situated in the Sudetes, a mountain range on the border of southern Poland and
northern Czech Republic. Two stations were used for the study, one at Śnieżka,
the highest peak in the Sudetes and the entire Czech Republic, and another station
at Serak in the Eastern Sudetes. The study also considered the Carpathian
Mountains, one of the longest and northernmost mountain ranges in Europe
associated with the Alpine orogenesis. Two meteorological stations were selected
for analysis, one at the summit of Łomnica in the Tatras and another in the
Southern Carpathians at Varful Omu (Makowski, 2006).
Fig. 1. Location of the stations.

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Tab. 1. List of meteorological stations
Station
name
Mountain
range
Altitude
[m a.s.l.] Coordinates
Łomnica Carphatians 2632 49°20N 20°21E
Serak Sudetes 1370 50°18N 17°11E
Śnieżka Sudetes 1602 50°73N 15°73E
Varful Omu Carphatians 2503 44°81N 14°98E
In this study, daily meteorological data were acquired from the OGIMET
dataset (https://www.ogimet.com/home.phtml.en). The research encompasses a
multi-year period spanning from 2005 to 2022, with a rigorous station selection
process based on data completeness criteria. The analysis hinged on daily data,
encompassing parameters such as air temperature (average, minimum,
maximum), mean wind speed, relative humidity, total precipitation, snow cover
depth, horizontal visibility, and the count of days with thunderstorms and fog.
From these datasets, fundamental climatic characteristics were computed,
including the annual mean air temperature, winter mean air temperature, number
of winter days (cold and very cold), annual precipitation totals, count of snow-
covered days, and maximum snow depth during the season. Additionally, for each
examined year, the average wind speed, horizontal visibility, and the annual count
of days with thunderstorms and fog were determined. The winter period was
defined as a three-month interval from December of the previous year to February
of the following year, with winter days categorized as cold (tmax ≤ -10.0 °C) or
very cold (tmax < -10.0 °C). Subsequently, bioclimatic conditions were analyzed
using selected indices on both annual and winter scales. Two indices were
considered: the wind chill index (WCI) (Table 2) and the Osokin climate severity
index (So) (Table 3), the latter being exclusively applied during the winter period
(Kozłowska-Szczęsna et al., 1997, from Gregorczuk, 1976; Osokin, 1968). The
calculation of the WCI utilized the following formula:
WCI = (10 v-2 + 10.45 - v) * (33 - t) 1.163, (1)
where: is the – air temperature (°C) and v is the wind speed (m/s). The resulting
value of the WCI indicates the sensation experienced by a person dressed in
clothing with a thermal insulation value of 4.0 clo (clo is the unit of thermal
insulation that is comfortable for a person).

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Table 2. WCI scale
Source: Gregorczuk (1976) and Kozłowska-Szczęsna et al. (1997).
The Osokin climate severity index (So) is computed using the following
formula:
So = (1 - 0.06 t) (1 + 0.20 v) (1 + 0.0006 Hk) F At , (2)
where t is the air temperature (°C), v is the wind speed (m/s), Hk is the absolute
elevation of the measurement station, F is the coefficient characterizing the
humidity of the air, and At is the daily air temperature amplitude. The values for
the humidity coefficient (F) are assigned as follows: relative humidity < 60% —
F = 0.90; 61–70% — F = 0.95; 71–80% — F = 1.0; 81–90% — F = 1.05; > 90%
— F = 1.10. Similarly, the daily air temperature amplitude (At) is assigned values
as follows: air temperature < 4.0 °C — At = 0.85; 4.1–6.0 °C — At = 0.90; 6.1–
8.0 °C — At = 0.95; 8.1–10.0 °C — At = 1.00; 10.1–12.0 °C — At = 1.05; 12.1–
14.0 °C — At = 1.10; 14.1–16.0 °C — At = 1.15; 16.1–18.0 °C — At = 1.20; >
18.1 °C — At = 1.25.
WCI (Wm-2) Thermal sensation
≤ 58.2 extremely hot
58.3–116.3 hot
116.4–232.6 excessively warm
232.7–581,5 comfortably
581.6–930.4 cool
930.5–1628.2 cold
1628.3–2326.0 frosty
> 2326.0 extremely frosty

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Table 3. Osokin climate severity index scale
So Climatic severity
< 1.0 mild
1.0–2.0 low severe
2.01–3.0 moderately severe
3.01–4.0 severe
4.01–5.0 very severe
5.01–7.0 extremely severe
> 7.01 exceptionally severe
Source: Osokin (1968) and Kozłowska-Szczęsna et al. (1997).
For each of the parameters, the direction and rate of change over the multi-
year period under investigation were determined. Additionally, the statistical
significance of these changes was assessed using a t-student test at a significance
level of p < 0.05. All maps, charts, and calculations were generated using the R
programming language.
3. Results
3.1. Climatic conditions
The climate of the mentioned stations exhibits significant thermal variability.
There are notably lower average air temperatures in the Carpathian Mountains
compared to the Sudetes. The annual average air temperature at high-altitude
stations in the Carpathians was -2.5 °C at Łomnica and -1.4 °C at Varful Omu
(Fig. 2). The difference in the average air temperature between these stations is
due to the lower geographical latitude of Varful Omu. On the other hand, in the
Sudetes, the annual average air temperature on Śnieżka during the study period
was 1.7 °C, which is nearly 2 °C lower than at Serak (3.6 °C). The significantly
higher elevation of Śnieżka results in much harsher thermal conditions compared
to Serak. The lowest annual air temperature values ranged from -3.3 °C at
Łomnica in 2005 to 2.6 °C at Serak in 2013. In three out of four stations, the
warmest year occurred in 2014 at Łomnica (-1.3 °C), Śnieżka (2.7 °C), and Serak
(4.7 °C). On Varful Omu, the warmest year was recorded in 2018 (-0.2 °C). From
the analysis conducted, it can be concluded that there was an increase in the annual
average air temperature at all the considered stations during the study period. This
increase was most pronounced at Łomnica, with a rate of 0.49 °C/10 years, and at
Varful Omu, with a rate of 0.59 °C/10 years. These changes were statistically
significant only at the Carpathian stations.

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Fig. 2. The course of the average annual air temperature.
Particular attention should be given to the winter air temperature patterns.
Over the study period, there was a relatively large difference in thermal conditions
between the selected stations in Central Europe. The average winter air
temperature at Łomnica was -9.6 °C, while at Varful Omu, it was -9.1 °C (Fig. 3).
Noticeably milder winters were observed at Śnieżka (-5.6 °C) and Serak (-4.5 °C).
The coldest winter was recorded during the 2011/12 season at Łomnica, with an
average temperature of -13.4 °C. In the same season, the coldest winter at Varful
Omu was slightly milder with an average air temperature of -12.,3 °C. In the
Sudeten stations, the coldest winter occurred one year earlier during the
2009/10 season (-8.0 °C) at Śnieżka and (-7.8 °C) at Serak. The warmest winter
was recorded during the 2007/08 season at Łomnica (-7.8 °C) and Serak (-2.7 °C).
On Śnieżka and Varful Omu, the warmest winter occurred during the 2013/14
season, with average air temperatures of -3.2 °C and -6.9 °C, respectively. The
study revealed that the increase in average winter air temperature was more
pronounced than for the entire year. The most significant changes were observed
at Serak, with a rate of 0.63 °C/10 years, and at Varful Omu, with a rate of
0.73 °C/ 10 years. However, these changes were not statistically significant.

316
Fig. 3. The course of average air temperature in winter.
Frosty days were significantly more frequent than very frosty days, with an
average of 95 days at Serak and 106 days at Śnieżka (Fig. 4). At the higher-
altitude Carpathian stations, there were 139 frosty days at Varful Omu and 143 at
Łomnica. The highest number of these days was recorded in 2022 at Łomnica
(166 days) and 122 days at Serak. The highest number of frosty days at Varful
Omu was in 2008 (165 days), while on Śnieżka, it was in 2021 (133 days). The
lowest occurrence of these days was in 2014, with only 71 days at Serak and 85
days at Śnieżka. On average, the number of very frosty days during the study
period ranged from 5 days at Serak to 35 days at Łomnica. The most extreme
conditions in this regard were observed in 2005, with 48 very frosty days at Varful
Omu and 57 at Łomnica. The research showed an increase in the number of frosty
days at 3 out of 4 analyzed stations. The most significant changes in the number
of frosty days were observed at Śnieżka, with an increase of 7.1 days/10 years. A
decrease in the number of frosty days was observed at Varful Omu, with a
decrease of 3.5 days/10 years. In all the analyzed stations, a decrease in the
number of very frosty days was recorded. The most significant changes occurred
at Varful Omu, with a decrease of 7.2 days/10 years, and at Łomnica, with a
decrease of 6 days/ 10 years. However, these observed changes were not
statistically significant.

317
Fig. 4. The course of the number of frosty and very frosty days.
In terms of precipitation, the analyzed stations had similar values, except for
the Łomnica station in the Carpathians. Over the study period, the average annual
precipitation totaled 1052 mm at Serak, 1058 mm at Varful Omu, and 1102 mm
at Śnieżka. A significantly higher amount of precipitation was recorded at
Łomnica, with 1965 mm (Table 4). The lowest annual precipitation total was
observed in 2011 at Varful Omu, with 752 mm, and in 2014 at Serak, with
825 mm. The highest annual precipitation total was recorded in 2017 at Varful
Omu, with 1400 mm, and at Łomnica, with 2397 mm. The longest duration of
snow cover was observed at Varful Omu, lasting 214 days, and at Łomnica,
lasting 251 days. The shortest duration of snow cover was on average 158 days at
Serak. The shortest snow cover occurred during the 2014/15 winter season at
Serak (133 days), while the longest was in the 2013/14 season (278 days) at
Łomnica. There was a considerable variation in the maximum snow cover
thickness over the study period. On average, the maximum snow cover thickness
ranged from 118 cm at Serak to 272 cm at Łomnica. The thinnest maximum snow
cover during the study period was in the 2013/14 season at Serak (42 cm), while
the thickest was in the 2008/09 season at Łomnica (407 cm).

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Table 4. Accumulated atmospheric precipitation [mm] (A), Number of days with snow
cover (B), Number of the days with maximum snow cover thickness [cm] (C). The color
blue indicates the lowest value of each parameter for the stations during the studied multi-
year period, while red represents the highest value.
Łomnica Serak Śnieżka Varful Omu
Year/Season A B C A B C A B C A B C
2005 | 2005/06 1575 245 258 1037 174 225 1213 188 152 1029 228 190
2006 | 2006/07 2027 224 403 1181 142 93 1177 162 237 791 221 182
2007 | 2007/08 2325 277 328 1098 186 82 1241 205 118 863 231 240
2008 | 2008/09 1791 273 407 1094 170 178 1006 188 99 1061 221 174
2009 | 2009/10 2308 248 222 1035 167 108 1180 183 79 1134 222 142
2010 | 2010/11 2039 262 94 1191 150 96 1301 178 99 1302 219 136
2011 | 2011/12 1399 243 260 868 154 164 836 155 50 752 200 110
2012 | 2012/13 1674 237 264 1007 158 120 1172 178 189 987 191 176
2013 | 2013/14 1726 278 205 1066 138 42 1277 178 152 1064 208 124
2014 | 2014/15 1934 230 213 945 133 89 825 155 85 1002 197 172
2015 | 2015/16 1845 237 208 856 154 94 956 153 112 876 215 236
2016 | 2016/17 1948 263 302 1124 174 66 1006 162 148 1226 237 110
2017 | 2017/18 2397 246 246 1028 155 98 1178 199 103 1400 228 219
2018 | 2018/19 1855 236 284 912 163 159 846 170 122 1188 210 146
2019 | 2019/20 2142 244 278 1191 135 92 1274 186 199 1056 195 72
2020 | 2020/21 2141 267 322 1256 164 104 1095 177 247 1130 230 196
2021 | 2021/22 2079 256 292 1092 178 101 1203 169 144 1251 214 223
2022 2157 1049 1043 183 942
Mean 1965 251 272 1057 158 118 1102 176 138 1058 214 170
Among the other meteorological elements, wind speed stands out as an
important factor influencing human thermal perception. Its average value was
21 km/h at Serak, 22 km/h at Łomnica, 28 km/h at Varful Omu, and a substantial
42 km/h at Śnieżka (Table 5). The highest average annual wind speed was
recorded in 2008, reaching 54 km/h at Śnieżka. Horizontal visibility exhibited
minor variations between the mentioned stations, except for the Łomnica station,
where the average annual horizontal visibility was 33 km. In the other stations,
horizontal visibility ranged from 19 to 20 km. A significant difference is observed
in the number of foggy days. The average annual number of foggy days ranged
from 266 days at Łomnica to 305 days at Śnieżka. In the most anomalous year at
Varful Omu, fog was present for almost 11 months, with 333 foggy days in 2009.

319
Fog occurred least frequently in 2006 at Łomnica, with 239 foggy days on record.
On average, the number of days with thunderstorm ranged from 24 days at Serak
to 47 days at Varful Omu. Thunderstorms were most frequent in 2010 at Varful
Omu (60 days) and least frequent at Serak in 2022 (13 days).
Table 5. Average wind speed [km/h] (A), Average horizontal visibility [km] (B), Number
of days with thunderstorm (C), Number of days with fog (D). The color blue indicates the
lowest value of each parameter for the stations during the studied multi-year period, while
red represents the highest value.
3.2. Bioclimatic conditions
Łomnica Serak Śnieżka Varful Omu
Year A B C D A B C D A B C D A B C D
2005 25 37 17 257 23 24 16 231 46 18 22 298 32 17 55 311
2006 23 36 22 239 23 19 16 254 51 18 29 282 34 15 50 314
2007 24 37 32 260 24 19 28 260 52 16 40 302 38 19 48 296
2008 28 35 24 270 23 19 22 269 54 16 22 315 32 18 45 308
2009 21 27 21 275 22 17 30 281 38 15 38 305 32 16 55 333
2010 23 29 23 278 21 14 26 283 37 13 26 311 32 17 60 322
2011 21 33 31 244 20 21 33 259 40 20 32 291 28 21 37 289
2012 23 33 30 262 22 20 36 272 41 19 31 310 28 24 43 265
2013 19 31 26 260 20 16 17 290 36 15 23 321 27 17 44 305
2014 19 31 22 286 20 18 34 291 37 18 34 327 27 21 43 307
2015 21 32 25 255 21 19 18 253 41 20 17 305 26 20 31 287
2016 21 30 34 288 19 18 21 283 37 19 22 314 26 18 49 326
2017 23 34 32 261 20 20 28 274 43 20 31 325 26 19 48 309
2018 19 34 43 269 22 22 27 261 38 24 26 292 24 19 48 302
2019 22 34 35 283 21 22 26 271 42 21 23 306 26 18 59 303
2020 21 38 28 260 21 25 21 256 41 23 26 285 24 22 41 289
2021 21 35 30 275 19 23 14 266 38 20 26 311 26 19 36 303
2022 22 38 24 277 19 25 13 270 41 22 22 293 25 20 50 305
Mean 22 33 28 266 21 20 24 268 42 19 27 305 28 19 47 304

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The values of the wind chill index (WCI) exhibited relatively consistent trends
over the study period (Fig. 5). All the years in the four stations were classified as
cold conditions. The highest average annual WCI value was 1226 W/m2 at
Śnieżka, while the lowest was 1000 W/m2 at Serak. The mildest conditions were
observed in 2014 at Serak (949 W/m2). On the other hand, the most severe
conditions were recorded in 2006 at Varful Omu, with an average WCI value of
1308 W/m2. All the analyzed stations showed a decrease in WCI values during the
study period, and these changes were statistically significant in all cases. The
observed changes amounted to 27 W/m2/10 years at both Śnieżka and Serak, and
48 W/m2/10 years at Łomnica. The most significant changes were observed at
Varful Omu, with a decrease of 51 W/m2/10 years.
Fig. 5. The course of the wind chill index over the study period.
Significantly higher wind chill index (WCI) values were recorded in the
Carpathians during the winter season (Fig. 6). These conditions were
predominantly cold, with a few seasons classified as frosty. The frosty winters
included the 2005/06, 2006/07, and 2011/12 seasons at Varful Omu, as well as
the 2011/12 season at Łomnica and Śnieżka. In an average winter season, the WCI
values ranged from 1333 W/m2 at Serak to 1569 W/m2 at Varful Omu. The most

321
severe conditions were observed in the 2011/12 season at Śnieżka (1726 W/m2)
and Varful Omu (1743 W/m2). In the 2016/17 season at Serak, the mildest
conditions were recorded, with a WCI value of 1277 W/m2. The analysis showed
a clear decrease in WCI values over the study period, ranging from
14 W/m2/10 years at Łomnica to 55 W/m2/10 years at Varful Omu. However,
these observed changes were not statistically significant.
Fig. 6. The course of the wind chill index in winter.
The climate severity index values by Osokin during the winter season were
classified as very severe, extremely severe, and predominantly exceptionally
severe (Fig. 7). The first two severity classes were exclusively recorded at the
Serak station, while the other stations exhibited predominantly exceptionally
sharp conditions. The average value of the climate severity index during the
winter season ranged from 5.4 at Serak to 11.4 at Varful Omu. At Łomnica and
Śnieżka, the values were 9.5 and 9.6, respectively. The mildest winter was
recorded in the 2016/17 season at Serak (4.9), while the most severe winter
occurred in the 2018/19 season at Varful Omu (16.1). The research indicated a
decrease in the climate severity index values at three of the analyzed stations,
except for Łomnica. These changes ranged from 0.1/10 years at Łomnica to

322
1.4/10 years at Varful Omu. However, these changes were not statistically
significant except for the Serak station.
Fig. 7. The course of the Osokin climate severity index in winter.
4. Summary and discussion
The average annual air temperature varied from -2.5 °C at the Carpathian Łomnica
station to 3.6 °C in the Sudetes at the Serak station. Meanwhile, on the highest peak
in the Sudetes, Śnieżka, the average annual air temperature was 1.7 °C. It is worth
noting that Urban and Tomczyński (2017) reported slightly different results in their
study on changes in the average air temperature at Śnieżka from 1881 to 2012. In
their study period, the average air temperature was 0.5 °C, with the highest values
occurring in 2006 and 2011 (2.3 °C). However, in the current study, it was shown
that 2014 was the warmest year at Śnieżka (2.7 °C). Particular attention should be
paid to the Łomnica and Serak stations, where the coldest and warmest years in the
study period were recorded. This occurred in 2005 at Łomnica, where -3.3 °C was
recorded, and in 2013 at Serak, with a value of 2.6 °C. All mountain stations
exhibited a significant increase in the average annual air temperature. The most
pronounced changes were observed in the Carpathians at Varful Omu

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(0.59 °C/10 years) and at Łomnica (0.49 °C/10 years). Previous studies also pointed
to a significant increase in air temperature on high-altitude stations. Micu and Micu
(2006) observed a temperature increase of 2.4 °C at the Varful Omu summit in the
period from 1961 to 2003. Similarly, changes at Śnieżka amounted to 0.1 °C/10 years
from 1881 to 2012 (Urban and Tomczyński, 2017).
During the winter season, the average air temperature ranged from -9.6 °C
at Łomnica to -9.1 °C at Varful Omu, with -4.5 °C recorded at Serak. Similar
results were obtained by Micu and Micu (2006), who, for the period from 1961 to
2003 at Varful Omu, reported a seasonal average air temperature of -9.2 °C. The
coldest winter was observed in the 2011/12 season at Łomnica (-13.4 °C), while
the warmest occurred in the 2007/08 season at Serak (-2.7 °C). The winter period
was characterized by a significant increase in the average air temperature, ranging
from 0.43 °C/10 years at Łomnica and 0.52 °C/10 years at Śnieżka to
0,73 °C/10 years at Varful Omu. A lower increase in the average air temperature
at Śnieżka during the period from 1881 to 2012 was noted by Głowicki (2008),
who reported an increase of 0.09 °C/10 years. Meanwhile, Tomczyk and Miś
(2023) identified an increase of 0.25 °C/10 years from 1966 to 2021.
The increase in the average air temperature significantly influenced the
frequency of winter days. The average number of frosty days ranged from 95 at
Serak to 143 at Łomnica. Meanwhile, the number of very frosty days varied from
5 at Serak to 35 at Łomnica. In most cases, there was an increase in the number
of frosty days and a decrease in very frosty days, except for Varful Omu, where a
significant decrease in the number of frosty days was observed during the study
period. On average, Śnieżka recorded 106 frosty days and 9 very frosty days.
Głowicki (2008) observed slightly higher frequencies of winter days at Śnieżka
for the period from 1951 to 2007. He recorded 129 frosty days and 12 very frosty
days, which showed a decreasing trend during the study period.
The lowest average annual precipitation in the study period was recorded at
the Sudeten station Serak (1057 mm), while the highest was observed at the
Carpathian station Łomnica (1965 mm). The snow cover lasted the shortest time
at the peak of Serak (158 days), while it persisted the longest at Łomnica
(251 days). Similar results were obtained by Szyga-Pluta and Mendel (2023) in
their study on meteorological conditions at Szrenica in the years 2018–2020. The
authors showed that during the study period, the snow cover at the Sudeten
measurement station lasted on average for 160 days per year. Among all the
stations studied, the thinnest snow cover was typically observed in the Eastern
Sudetes at Serak (118 cm), while the thickest cover was recorded at Łomnica
(272 cm). The lowest horizontal visibility was observed at Śnieżka and Varful
Omu (19 km), while the highest was recorded at Łomnica (33 km). Fog was least
frequently present at Łomnica (266 days per year), while it was most frequently
observed at Śnieżka (305 days per year). On the other hand, thunderstorms were
least frequently observed at Serak, occurring on average for 24 days per year.

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They were most frequently recorded at the Carpathian station Varful Omu, with
an average of 47 days per year.
The bioclimate of the studied high mountain peaks, as represented by the
wind chill index (WCI), was characterized by cold conditions. The mildest
conditions were observed in the Sudetes at the Serak peak (949 W/m2). On the
other hand, the harshest conditions were observed at Śnieżka (1226 W/m2). The
lowest average annual WCI value was recorded in 2014 (949 W/m2) at Serak,
while the highest was in 2006 at Varful Omu (1308 W/m2). Winter conditions
were significantly harsher, confirming the occurrence of cold and frosty winters
based on the wind chill index. Frosty winters were observed infrequently at Varful
Omu, Łomnica, and Śnieżka. The most severe average winter conditions were
observed at Varful Omu (1569 W/m2), while the mildest were recorded at Serak
(1333 W/m2). Both for the entire year and for the winter period, a decrease in WCI
values was observed, with the most significant changes noted at Varful Omu
(51 W/m2/10 years for annual values and 55 W/m2/10 years for winter values).
Błażejczyk et al. (2020), analyzing bioclimatic conditions based on the universal
thermal climate index, UTCI in the Northern Carpathians, found that the station
at Łomnica had the most severe conditions in the studied area. The average UTCI
value in the period from 1986 to 2015 was -15.7 °C, while the minimum daily
value of this index was as low as -73.5 °C. Next, an analysis of the Osokin climate
severity index was conducted for the winter period. The high mountain stations
under consideration exhibited conditions ranging from very severe to
exceptionally severe, with winters primarily classified as exceptionally severe.
The average value of the index during the winter period ranged from 5.4 at Serak
to 11.4 at Varful Omu. The most severe winter was recorded in the 2018/19 season
at Varful Omu, with a climate severity index value of 16,1. On the other hand, the
mildest winter was observed in the 2016/17 season at Serak, with a severity index
value of 4.9. In most of the studied stations, a decrease in the severity index value
was demonstrated, except for Łomnica. Changes ranged from 0.1/10 years at
Łomnica to 1.4/10 years at Varful Omu.
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