Durability of snow cover and its long-term variability in the Western Sudetes Mountains (original) (raw)

Abstract

This paper presents the results of the analysis of the Western Sudetes' snow cover temporal and spatial changes, as well as it demonstrates the research on the long-term trends in the changes of snow cover durability. In order to conduct the study, the coefficient of snow cover durability (V) was used, which was defined as the quotient of the actual and the potential time of snow cover duration and expressed in percentage (1-100%). Moreover, the frequency of total disappearance of snow cover was established for the optimal winter season (December-March). Measurement data were obtained from 17 stations in the 1961-2015 period. The snow cover on the Western Sudetes' slopes with southern (S) macro-exposure lasts longer (has greater durability) than on the slopes in analogous altitude zones with northern (N) macro-exposure. At the altitudinal level of 600-700 m a.s.l., where the differences are the biggest, the average V values range from 60% at stations N to 75% in stations S. In the analysed area, excluding the upper ranges, slight negative trends in V changes have been noted. Snow cover persists for a shorter and shorter time. For the substantial majority of the stations, the trends in these changes are not statistically significant at the 0.05 level of statistical significance. They refer to the tendencies in other mountainous regions in Poland and Europe. Analogously, the stations with S macro-exposure, located at similar altitudes as stations with N macro-exposure, are characterised by two to three times lesser frequency of total disappearance of snow cover. Coefficient V is negatively correlated with the total disappearance of snow cover. At the stations with S macroexposure in the Western Sudetes, these correlations are usually strong or very strong, whereas at the stations with N macro-exposure, at similar altitudes, they are usually moderate or very weak.

Figures (14)

Table 1 Characteristics of weather stations

Table 1 Characteristics of weather stations

These were Sobik et al. (2014), as well as Urban et al. (2018), who pointed out to the fact that in the Karkonosze Mountains the essential differences in precipitation at similar altitudes exist not in the east-west direction, but between the southern of northern sides of the mountains. Also, they emphasised the increase in winter precipitation in the upper river catchment of the Kamienna and in the western part of the Polish Karkonosze. This should be accounted for by the The big denivelation of over 1250 m (from the station Jelenia Gora, located in a valley, to the highest peak Sniezka) and the great variety of the topography of the area, as well as the exposure of the station cause the noticeable spatial variety of V value. This variety results from many factors, as in the case of snowiness and severity index of winters (Urban et al. 2018), including altitude and orographic deformation of the flow field of air masses that shape precip- itation and air temperature. In consequence of this deforma- tion, there emerges the distinct contrast between the snowiness in the river catchment of the Elbe (S, SW and W macro- exposures) compared with the Odra river catchment (NE and N macro-exposures). The areas with SW and W exposures are characterised by the longer period of retention and bigger depth of snow cover. This result corresponds with the previous study on the thermal and precipitation variety of the Karkonosze Mountains (Sobik et al. 2014) or of the Karkonosze and the Izera Mountains (Urban et al. 2018). This contrast stands out especially in the altitude range of 500-900 m a.s.l. (Fig. 2). In the upper ridges, the differences are becoming less distinguishable due to the snow blowing alternately from one to the other side of the range.

These were Sobik et al. (2014), as well as Urban et al. (2018), who pointed out to the fact that in the Karkonosze Mountains the essential differences in precipitation at similar altitudes exist not in the east-west direction, but between the southern of northern sides of the mountains. Also, they emphasised the increase in winter precipitation in the upper river catchment of the Kamienna and in the western part of the Polish Karkonosze. This should be accounted for by the The big denivelation of over 1250 m (from the station Jelenia Gora, located in a valley, to the highest peak Sniezka) and the great variety of the topography of the area, as well as the exposure of the station cause the noticeable spatial variety of V value. This variety results from many factors, as in the case of snowiness and severity index of winters (Urban et al. 2018), including altitude and orographic deformation of the flow field of air masses that shape precip- itation and air temperature. In consequence of this deforma- tion, there emerges the distinct contrast between the snowiness in the river catchment of the Elbe (S, SW and W macro- exposures) compared with the Odra river catchment (NE and N macro-exposures). The areas with SW and W exposures are characterised by the longer period of retention and bigger depth of snow cover. This result corresponds with the previous study on the thermal and precipitation variety of the Karkonosze Mountains (Sobik et al. 2014) or of the Karkonosze and the Izera Mountains (Urban et al. 2018). This contrast stands out especially in the altitude range of 500-900 m a.s.l. (Fig. 2). In the upper ridges, the differences are becoming less distinguishable due to the snow blowing alternately from one to the other side of the range.

Nonetheless, in the wide slope zone 600—700 m, the vari- ability of coefficient V varies significantly. This is especially noticeable in the zone 600—700 m (Harrachov, Vysoké nad Jizerou), where the stations with macro-exposure S are

Nonetheless, in the wide slope zone 600—700 m, the vari- ability of coefficient V varies significantly. This is especially noticeable in the zone 600—700 m (Harrachov, Vysoké nad Jizerou), where the stations with macro-exposure S are

Table 2 The coefficient of snow cover durability and its standard deviation (4), coefficient of variability (Vz) and frequency (N) of seasons with stable and unstable snow cover

Table 2 The coefficient of snow cover durability and its standard deviation (4), coefficient of variability (Vz) and frequency (N) of seasons with stable and unstable snow cover

The calculated trends of V changes are negative for most of the analysed stations in the Western Sudetes (Table 3). This means that the values of V successively decreased, indicating at the same time, that the time of retention shortened in suc- cessive winters. This result is confirmed by the previous study on snow cover in Sniezka in the period 1901-2000 (Glowicki 2005) or in the Polish Sudetes and their foreland in 1951— 2007 (Urban 2015, 2016). The pace of decrease fell within the range from ca. — 0.6% points (pp)/decade in station Desnd—Sous to ca. — 2.7 pp/decade in Swieradow Zdrdj sta- tion or even —3.1 pp/decade in station Horni MarSov. The average pace of the drop of coefficient V for all stations for which its trends of changes were determined was — 1.43 pp/ decade (Table 3). The trend of V change is statistically signif- icant at the p=0.05 significance level merely for one out of eight stations which were selected for the analysis of snow conditions (Table 3). A slight decreasing trend in the charac- teristics of snow cover was observed in most of Polish area in the second half of the twentieth century. The changes in snow cover relate to the changes in the atmospheric circulation and especially with the increased frequency of the advection of air masses from the western sector (Falarz 2004). The more fre- quent occurrence of winters with a relatively low V coefficient might be related to the changes in atmospheric circulation

The calculated trends of V changes are negative for most of the analysed stations in the Western Sudetes (Table 3). This means that the values of V successively decreased, indicating at the same time, that the time of retention shortened in suc- cessive winters. This result is confirmed by the previous study on snow cover in Sniezka in the period 1901-2000 (Glowicki 2005) or in the Polish Sudetes and their foreland in 1951— 2007 (Urban 2015, 2016). The pace of decrease fell within the range from ca. — 0.6% points (pp)/decade in station Desnd—Sous to ca. — 2.7 pp/decade in Swieradow Zdrdj sta- tion or even —3.1 pp/decade in station Horni MarSov. The average pace of the drop of coefficient V for all stations for which its trends of changes were determined was — 1.43 pp/ decade (Table 3). The trend of V change is statistically signif- icant at the p=0.05 significance level merely for one out of eight stations which were selected for the analysis of snow conditions (Table 3). A slight decreasing trend in the charac- teristics of snow cover was observed in most of Polish area in the second half of the twentieth century. The changes in snow cover relate to the changes in the atmospheric circulation and especially with the increased frequency of the advection of air masses from the western sector (Falarz 2004). The more fre- quent occurrence of winters with a relatively low V coefficient might be related to the changes in atmospheric circulation

Table 3. Change trend magnitude, correlation coefficient (R) and the statistical significance of the coefficient of snow cover durability * Significant statistically at the 0.05 significance level types over the Northern Atlantic. The growth of zonal cyclon- ic circulation from the south-western direction in last decades of the twentieth century was proved by Migala (2005) and Migala et al. (2016). This circulation generates in Western and Mid-Europe a vast atmospheric front with increased cloudiness and brings warming and precipitation in the cold season (Urban et al. 2018).

Table 3. Change trend magnitude, correlation coefficient (R) and the statistical significance of the coefficient of snow cover durability * Significant statistically at the 0.05 significance level types over the Northern Atlantic. The growth of zonal cyclon- ic circulation from the south-western direction in last decades of the twentieth century was proved by Migala (2005) and Migala et al. (2016). This circulation generates in Western and Mid-Europe a vast atmospheric front with increased cloudiness and brings warming and precipitation in the cold season (Urban et al. 2018).

0.0 to 0.7. In the stations with southern macro-exposure and at Sniezka Mt., they are significant statistically at the 0.05 significance level. The correlation coefficient is clearly dif- ferentiated depending on the macro-exposure and altitude (Table 5). Namely, the stations with southern macro- exposure (eg Bediichov, Harrachov, Horni MarSov) are characterised by the explicitly higher R values (0.7 + 0.5) than stations with northern macro-exposure (eg. Przesieka, Karpacz_2, Swieradéw Zdrdj), where R is in the range of 0.3 + 0.2. Thus, in the stations on the slopes of the Western Sudetes with southern macro-exposure, these features are usually strongly or very strongly correlated with each other, whereas in the stations with northern macro-exposure, the strength of the relationship is usually moderate or very weak. This is well illustrated by the correlations of the se- lected stations located at similar altitudes, but with opposite macro-exposures, i.e. Horni Mar8ov—Karpacz_2 and Harrachov—Przesieka (Fig. 8). In addition, the strongest correlation occurs in the middle parts of the slopes with macro-exposure S and SW. The weakest correlation (0.0 + 0.1) or even lack of it is shown by the stations with the lowest locations and northern macro-exposure, i.e. Hejnice and Jelenia Gora (Table 5). This is due to differ- ences (already mentioned in the study) in temperatures and winter precipitation in slope stations with opposite macro- exposures conditioned by the foehn effect and the altitude above sea level. with southern macro-exposure, there appeared more frequent foehn phenomena and the adiabatic warming of descending air on the leeward side of the orographic barrier. The advanc- ing frequency of the advection of polar and sea air masses from SW and W directions in the cold season in the Sudetes as well as their thermal and precipitation implications have already drawn attention of the researches in this field (Kwiatkowski 1972, 1975, 1979; Sobik et al. 2014; Urban et al. 2018). Although the correlation of the number of days with total disappearance of snow cover between Harrachov- Przesieka and Horni MarSov-Karpacz_2 stations is positive, it is clearly weaker than in the case of the V coefficients. The calculated correlation coefficient R for the common period 1983/1984—2010/2011 in the pairs of mentioned stations were 0.3.

0.0 to 0.7. In the stations with southern macro-exposure and at Sniezka Mt., they are significant statistically at the 0.05 significance level. The correlation coefficient is clearly dif- ferentiated depending on the macro-exposure and altitude (Table 5). Namely, the stations with southern macro- exposure (eg Bediichov, Harrachov, Horni MarSov) are characterised by the explicitly higher R values (0.7 + 0.5) than stations with northern macro-exposure (eg. Przesieka, Karpacz_2, Swieradéw Zdrdj), where R is in the range of 0.3 + 0.2. Thus, in the stations on the slopes of the Western Sudetes with southern macro-exposure, these features are usually strongly or very strongly correlated with each other, whereas in the stations with northern macro-exposure, the strength of the relationship is usually moderate or very weak. This is well illustrated by the correlations of the se- lected stations located at similar altitudes, but with opposite macro-exposures, i.e. Horni Mar8ov—Karpacz_2 and Harrachov—Przesieka (Fig. 8). In addition, the strongest correlation occurs in the middle parts of the slopes with macro-exposure S and SW. The weakest correlation (0.0 + 0.1) or even lack of it is shown by the stations with the lowest locations and northern macro-exposure, i.e. Hejnice and Jelenia Gora (Table 5). This is due to differ- ences (already mentioned in the study) in temperatures and winter precipitation in slope stations with opposite macro- exposures conditioned by the foehn effect and the altitude above sea level. with southern macro-exposure, there appeared more frequent foehn phenomena and the adiabatic warming of descending air on the leeward side of the orographic barrier. The advanc- ing frequency of the advection of polar and sea air masses from SW and W directions in the cold season in the Sudetes as well as their thermal and precipitation implications have already drawn attention of the researches in this field (Kwiatkowski 1972, 1975, 1979; Sobik et al. 2014; Urban et al. 2018). Although the correlation of the number of days with total disappearance of snow cover between Harrachov- Przesieka and Horni MarSov-Karpacz_2 stations is positive, it is clearly weaker than in the case of the V coefficients. The calculated correlation coefficient R for the common period 1983/1984—2010/2011 in the pairs of mentioned stations were 0.3.

Fig.6 The course of number of days with total disappearance of snow cover (A) at the stations: Harrachov—Przesieka (I) and Horni MarSov—Karpacz_2 (ID in the period December—March

Fig.6 The course of number of days with total disappearance of snow cover (A) at the stations: Harrachov—Przesieka (I) and Horni MarSov—Karpacz_2 (ID in the period December—March

In Karpacz_2 station in 1983/1984—2010/2011 winter seasor *Significant statistically at the 0.05 significance level Table 5 Pearson’s linear correlation values (R) and strength of the relationship between the snow cover durability coefficient and total snow disappearance in 1981/1982-2010/2011 winter season in the selected stations

In Karpacz_2 station in 1983/1984—2010/2011 winter seasor *Significant statistically at the 0.05 significance level Table 5 Pearson’s linear correlation values (R) and strength of the relationship between the snow cover durability coefficient and total snow disappearance in 1981/1982-2010/2011 winter season in the selected stations

Fig. 8 The relationship between snow cover durability coefficient (V) and total snow disappearance (A) in 1981/1982—2010/2011 winter seasons alongside their trend lines (black bold lines) and simple

Fig. 8 The relationship between snow cover durability coefficient (V) and total snow disappearance (A) in 1981/1982—2010/2011 winter seasons alongside their trend lines (black bold lines) and simple

regression equations in selected macro-exposure stations S (left column) and macro-exposure N (right column). Note: in Karpacz_2 station in 1983/1984—-2010/2011 winter seasons.

regression equations in selected macro-exposure stations S (left column) and macro-exposure N (right column). Note: in Karpacz_2 station in 1983/1984—-2010/2011 winter seasons.

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