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Climatic sensitivity of the non-glaciated mountains cryosphere (Tatra Mts., Poland and Slovakia)
Global and Planetary Change 121 (2014) 1–8
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Climatic sensitivity of the non-glaciated mountains cryosphere (Tatra Mts., Poland and Slovakia) Bogdan Gądek Department of Geomorphology, University of Silesia, Sosnowiec, Poland
a r t i c l e
i n f o
Article history: Received 21 July 2013 Received in revised form 18 June 2014 Accepted 1 July 2014 Available online 5 July 2014 Keywords: mountain cryosphere snow cover lake ice glacierets sporadic permafrost the Tatra Mountains
a b s t r a c t This paper concerns the response of the conditioned by orography cryosphere of the non-glaciated mountains of mid-latitude to the climate impulses. It presents the relationships among the air temperature, precipitation, snow cover, lake ice cover, firn-ice patches (glacierets) and permafrost in the Tatras. The data from the warmest multiyear in the history of the local meteorological measurements and statistical models (multiple regression) have been used. The results indicate that all the components of the contemporary cryosphere are very sensitive to the changes in the air temperature in winter or snow precipitation/accumulation. Due to the diverse orographic conditions, interannual variability of seasonal and perennial, surface and subsurface ice deposits in the mountain areas may not be synchronous. However, the long-term trends of this variability reflect the changes in the global climate system. © 2014 Elsevier B.V. All rights reserved.
1. Introduction The Earth's coating containing ice extends from the upper troposphere to the lower boundary of permafrost. Dobrowolski (1923) called it the cryosphere (from Greek κρύος — ice, frost) (Barry et al., 2011). It is an integral part of the climate system. Changes in the ice mass occurring in the Earth's environment are related to the transfers of energy and humidity between the atmosphere, hydrosphere and lithosphere. The accompanying feedback, in turn, affects the atmospheric and oceanic circulation (Barry and Gan, 2011). The main components of the cryosphere include cloud ice, snow, glaciers, ice caps and ice fields, ice sheets, the ice cover of the seas, lakes and rivers, and ice in the ground. They are different in terms of the place of occurrence, the role in the natural environment and the sensitivity to climate change. According to what geological and geomorphological data indicate, the changes in Earth's cryosphere occur in cycles of variable length. The contemporary phase of these changes is evidenced by the results of terrestrial and remote sensing monitoring of the main components of the cryosphere (e.g. IPCC, 2007). The noted decline in the mass of ice in the Earth's environment is a continuation of the global changes which began about 20,000–18,000 years ago (e.g. Hughes, 1998). In many mountains glaciated during the Pleistocene, the climatic snow line (CSL) nowadays runs over the highest peaks, and the only traces of the past glaciers are of the geomorphological nature. The results of the international monitoring of glaciers (Haeberli, 1998), carried out
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http://dx.doi.org/10.1016/j.gloplacha.2014.07.001 0921-8181/© 2014 Elsevier B.V. All rights reserved.
since 1894, reflect a further moving upward of the CSL and the subsequent deglaciation of the mountain areas (e.g. Zemp et al., 2008). The retreat of glaciers, however, facilitated the development of the periglacial components of the cryosphere. In the natural environment of the several, glaciated in the past mountains of mid-latitude, ice presently occurs not only seasonally but also perennially, both on and below the surface of the terrain. The relief affects the local radiation balance, the air circulation and precipitation patterns (Barry, 2009) and may facilitate the concentrated accumulation of snow and/or cold, which may result in respectively firn-ice patches (glacierets) and patches of permafrost. Because of a low temperature of ice melting, the recession of the cryosphere components is usually considered as the result of global warming. However, in the mountain environment, the relief, as a stable component of the climate system, may locally suppress the impact of global warming on the rate of ice melting. Moreover, a decrease in the occurrence duration and thickness of snow cover may also happen in consequence of a decrease in snowfall (e.g. López-Moreno, 2005; López-Moreno and Vicente-Serrano, 2007; Żmudzka, 2011). This may result in the recession of glacierets simultaneous with the aggradation of permafrost — regardless of the changes in the air temperature (Gądek, 2008; Gądek and Leszkiewicz, 2012). The cryosphere is not merely a collection of the ice components of the natural environment but it is an open, dynamic and complex system, which is characterized by the mass circulation and the associated energy, and which both responds to external impulses and impacts upon the environment. However, in the literature there is a lack of comprehensive studies on the functioning of the cryosphere of non-glaciated mountains, even though the changes are due to the current weather conditions (Fig. 1).
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The climate is sufficiently severe for the middle periglacial belt to be present above the upper timberline (Rączkowska, 2007). Sporadic and discontinuous permafrost may occur above 1700 m a.s.l. (Dobiński, 2005), but caves where ice masses are permanent are located above 1200 m a.s.l. (Siarzewski, 1994). In the second half of the twentieth century and in the first decade of the twenty-first century in the Tatra Mountains there was registered a decrease in the number of days with snow cover and in the maximum thickness of the snow cover, shortening of the duration and a reduction of the thickness of the lakes' ice cover, a considerable or total exchange of the glaciarets' mass, and degradation of the patches of permafrost. These changes were consistent with an increase in the air temperature in winter and summer seasons, and with a decrease in snowfall (Gądek, 2011). 3. Data and methods 3.1. Air temperature, precipitation and snow cover data
Fig. 1. The hierarchical model of relationships between climate and cryosphere in nonglaciated mountains.
The first such attempt has been made in this work. Its aim is to explore the statistical relationships among a long-term variability of the snow cover, lake ice, glacierets, permafrost, precipitation and the air temperature above the timberline in the Tatra Mountains for a better understanding of the processes that control the behavior of the contemporary mountain cryosphere. The study area belongs to the international network of biosphere reserves (UNESCO). It rises between the lower limit of sporadic permafrost (Dobiński, 2005) and CSL (Zasadni and Kłapyta, 2009) and is included in the group of important ice and snow regions in Europe (Voigt et al., 2010). The characteristics of the natural environment of the Tatra Mountains, the observational data on their variability since the Little Ice Age, and a well-developed infrastructure which has been providing a continuous service for climatologic research for decades — all of these predispose these mountains to the role of the reference area for monitoring global climate changes and their geoecological implications. 2. Regional setting The Tatra Mountains are the highest range in the Carpathians arc (Gerlach summit: 2655 m a.s.l.), and also the highest non-glaciated mountains between the European Alps, the Scandes and the Caucasus (Fig. 2). The cold periods of the Pleistocene caused several mountain glaciations (Baumgart-Kotarba and Kotarba, 2001; Lindner et al., 2003). The equilibrium line altitude (ELA; ≈ CSL) of Würmian glaciers during the period of their maximum range probably was about 1500 m a.s.l. (Makos and Nitychoruk, 2011). Currently, this altitude constitutes the upper timberline, while the contemporary CSL is located more than 1000 m above (Zasadni and Kłapyta, 2009). The orographic snow line at the northern side of the Tatras is delimited by firn-ice patches nourished by snow avalanches, down to 1530 m a.s.l. (e.g. Jania, 1997; Gądek, 2008). The present-day climate is transitional between maritime and continental influences. The mean annual air temperature (MAAT) at the northern and southern Tatras' foothills (ca. 850 m a.s.l.) is 6 °C and 8 °C respectively. In the highest summits (above 2600 m a.s.l.) MAAT is −4 °C (Hess, 1996). The mean total precipitation ranges from 1100 mm in the north foothills to 1900 mm in higher parts (Niedźwiedź, 1992) and the number of days with snow cover ranges from about 100 to 290 respectively (Hess, 1996). The ice cover on the lakes of the Tatras usually remains for 6 to 10 months. Sometimes, however, on the uppermost lakes (above 2000 m a.s.l.) it persisted throughout the year (e.g. Pacl and Wit-Jóźwikowa, 1974).
Daily values of the air temperature, precipitation and snow depth from the synoptic station located at the top of Kasprowy Wierch Mountain (WMO id: 12650) were applied. This meteorological station is the highest in Poland (1991 m a.s.l.) and the only one in the alpine zone of the Tatras (Fig. 2). The data were derived from the Global Historical Climatology Network accessible from the NOAA website. They included the hydrological years (October–September) of 1998–2010. The daily air temperature values were the bases for the calculation of the mean annual, winter and summer half-year air temperature (MAAT, MWAT and MSAT respectively), mean values of the winter (December– February), spring (March–May), summer (June–August), autumn (September–November) temperature and totals of positive degree days (PDD) in subsequent years. The daily precipitation totals were used to determine total annual and semi-annual precipitation, and total precipitation in the time of the increased snow cover (snowfall) and during the melt. However, the daily snow depth values were used to calculate the number of days with snow cover of ≥1 cm, as well as the seasonal maximum and total of the daily snow depth. 3.2. Lake ice cover, glacieret and permafrost data All the data refers to the hydrological years of 1998–2010. The analysis was focused on the duration and seasonal maximum thickness of the ice cover of Morskie Oko Lake (the data from the Institute of Meteorology and Water Management). This is the largest lake in the Tatras. It is located at an altitude of 1395 m a.s.l., it has the area of about 349,400 m2 and the capacity of approximately 9,935,000 m3 (Choiński et al., 2010). Photogrammetric methods were used to acquire data about the area and front altitude of the Medeny glacieret at the end of the ablation seasons. Each year stereoscopic images of the glacieret were taken with a non-metric camera, then they were calibrated with the method of direct linear transformation (Abdel-Aziz and Karara, 1971) and digitized using a digital analytical autograph. The Medeny glacieret is the largest, contemporary, perennial ice form in the Tatras, occurring on the surface of the area. It is located at an altitude of 2050 m a.s.l., at the place of N exposure (Fig. 2). The temperature of the active layer and permafrost in the Tatra Mountains are not monitored, and the measurement of the ground surface temperature (GST) in these areas have started only recently. Therefore the results of the statistical modeling of average GST values in consecutive years, winter and summer half-year (MAGST, MWGST and MSGST respectively) in the Medena kotlina were used for that purpose (Gądek and Leszkiewicz, 2012). This is the only place in the Carpathian Mountains where the permafrost existence has been evidenced not only with geophysical methods (GST, GPR, electromagnetic and DC resistivity measurement), but also outcrop of buried massive ice
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Fig. 2. Location of the investigation areas: I — Kasprowy Wierch Mt. (photo by W. Kaszkin), II — Morskie Oko Lake (photo by R.J. Kaczka), III — the Medena kotlina Valley (IIIa — the Medeny glacieret, IIIb — outcrop of buried massive ice).
have been found, and its development monitored together with morphodynamics of the slope (Gądek and Grabiec, 2008; Gądek et al., 2009).
the dependent variable with making allowance for the number of used independent variables. 4. Results
3.3. Statistical methods In order to examine the sensitivity of the individual elements of the Tatras' cryosphere to the changes in the air temperature and precipitation, the methods of descriptive statistics, correlation and multiple regression are applied. Firstly, minimum and maximum values, arithmetic means with standard errors and standard deviations of all the data on temperature, precipitation and cryosphere were determined. The year-on-year changes in the variables have been calculated, and their distribution tested. Then, the analyzed data were standardized and put through the cross-correlation (Pearson and Spearman) together with checking its statistical significance with the t test. Basing on the disclosed correlations (the level of significance α ≤ 0.05) the equation of multiple linear regression has been developed (with the method of least squares) to describe the relationship between the variability of individual cryosphere components and the air temperature or/and precipitation. In each case, there have been calculated: the coefficient of correlation (r), the level of statistical significance (p), and the adjusted coefficient of determination (adj r2), which indicates to what degree the statistical model (regression equation) explains the variability of
The changes in the air temperature, precipitation, snow cover, lake ice, glacieret and GST at the permafrost site registered in the mountains in the years of 1998–2010, are illustrated in Fig. 3, whereas the correlation between these components of the climate and cryosphere are presented in Figs. 4 and 5. 4.1. Variability of the climate and cryosphere components 4.1.1. Variability of the climate components In the analyzed period, MAAT at Kasprowy Wierch varied from − 0.63 °C (in 2004) to 1.06 °C (in 2007). The values of arithmetic mean (± standard error) and standard deviation were respectively: −0.03 (±0.13) °C and 0.46 °C. In 2004, extremely low values of MSAT and the amount of the PDD were recorded, whereas the coldest spring, summer and autumn occurred in 1998, the coldest winter — in 2010. The coldest winter half-year was in 2005 and 2006. In 2007, the winter half-year was unusually warm (both winter and spring), while the summer was only about 0.2 °C cooler than the warmest summer in 2002. The warmest summer half-year, however, was in 2000, when the
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Fig. 3. Variability of the climate and cryosphere components in the Tatra Mountains.
largest amount of the PDD and the average temperature of the autumn. In 2004 and 2007, the greatest changes in the year-on-year air temperature were noted. In the first case, the values of MSAT, summer temperature and total PDD decreased respectively by 1.28 °C d, 2.06 °C d and 202.5 °C d, while in the second case the values of MAAT and MSAT increased respectively by 2.26 °C and 2.7 °C (Fig. 3a–b). The total annual precipitation in the period of the analyzed 13 years was changing from 1373 mm (in 2003) to 2340 mm (in 2001). The arithmetic mean and standard deviation were as follows: 1756 (±74.21) mm and 267 mm. In the year 2003, precipitation was particularly low during the development of the snow cover. However, the lowest amounts of precipitation in the winter and summer half-year were reported in 2006 and 1999 respectively. In the winter half-year of 2006 an exceptionally large year-on-year change in total precipitation (a decline by 239 mm), while the biggest change of total snowfall occurred in 1999 (an increase by 466 mm). However, in the summer half-year of 2001 an extreme increase in precipitation was registered. The total was up to 740 mm higher than in the previous year. The highest precipitation in the winter half-year, including snowfall, occurred in 1998 (Fig. 3c–d).
4.1.2. Variability of the cryosphere components The number of days with the snow cover on Kasprowy Wierch Mountain ranged from 199 (in 2009) to 268 (in 1999). The maximum thickness of the snow cover was changing at that time from 140 cm to 325 cm reaching extreme values in two consecutive winter seasons in 2001 and 2000. In the same seasons the minimum and maximum totals of daily snow cover thickness were recorded (Fig. 3e). They amounted to 10,840 cm d and 30,693 cm d respectively. The mean thirteen-year-old value of the total of the seasonal snow cover thickness was 21,259.5 (±1608.5) cm d, and the standard deviation was equal to 5799.5 cm d. The ice cover of Morskie Oko Lake was formed in the months of November–December, and disappeared in the months of April–May. The duration of the total icing ranged from 112 days (in 2001) to 172 days (in 2006). The maximum seasonal thickness of the ice at the monitored site varied from 40 cm (in 2000) to 114 cm (in 2008). The mean values of these parameters of the ice cover amounted to 140 (±5) days and 60.38 (±5.88) cm whereas the standard deviations — 19 days and 21.19 cm. The biggest year-on-year changes in the number of days with the ice cover were registered in 2007 (a decrease by
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Fig. 4. The relationships between interannual variability of the Tatra Mountains cryosphere components, their climatic sensitivity and results of statistical modeling (standardized data).
49 days) and 1999 (an increase by 43 days), and in the maximum thickness of the ice in 2008 (an increase by 50 cm) and 2010 (a decrease by 41 cm) (Fig. 3f). The area of the Medeny glacieret in autumn seasons varied from 12,400 m2 (in 2003) to 28,100 m2 (in 2009). The arithmetic mean and standard deviation were 21,500 (±1200) m2 and 4300 m2 respectively. By 2003 the glacieret had been in clear recession, then quickly reached the size equal to that of the end of the 90s of the twentieth century. The biggest changes in its area took place in 1999 (it decreased by 9000 m2) and 2004 (increased by 8900 m2). The year 2004 saw a record-breaking change in the position of the front of the glacieret. Its range increased then by 88 m (Fig. 3g). The results of statistical modeling indicate that in the Medena kotlina at the site of permafrost occurrence MAGST varied from −0.58 °C (in 2004) to 0.27 °C (2001 and 2007). The arithmetic mean
and standard deviation were −0.27 (±0.07)°C and 0.25 °C respectively. MWGST ranged from − 4.9 °C (in 2006) to − 3.3 °C (in 2007). The change of the average GST in the two winter half-years was record high, whereas the minimum and maximum MSGST amounted to 3.13 °C (in 2004) and 4.47 °C (in 2000). Both of these values were extremely different from the average GST of the previous summer half-year (Fig. 3h). 4.2. Climatic sensitivity of the cryosphere components 4.2.1. Snow cover The most comprehensive index of how snowy the winter is — the total thickness of the seasonal snow cover — depends on the duration of the snow cover and its daily thickness. In the analyzed period, the value of this ratio depended mainly on the thickness of the snow
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total of its daily thickness). This relationship is demonstrated by the equation: δAreaGlac ¼ 0:45 δDMax
Sn −0:54
δΣPDD ðr ¼ 0:81; pb0:008Þ
ð3Þ
where: AreaGlac — the area of the glacieret, DMax Sn — the seasonal maximum of the snow cover thickness, ΣPDD — the total of positive degree days. Model (3) explained 58% (adj r2) of the variability of the described variable (Fig. 4i).
Fig. 5. The relationships between interannual variability of seasonal and perennial components of the Tatra Mountains cryosphere (standardized data).
cover (Fig. 4a). The number of days with the snow cover was of lesser importance. Interannual changes in the total thickness of the seasonal snow cover on Kasprowy Wierch were primarily associated with the changes in the amount of snowfall. Moreover, statistically significant was also the effect of rainfall during the snow-melt period and the air temperature in the winter (Fig. 4b). This correlation is illustrated by the linear regression:
4.2.4. Permafrost In the Medena kotlina, at the site of permafrost occurrence, MAGST was more influenced by the temperature of the ground in the winter half-year than in the summer half-year (Fig. 4j–k). It was the result of the higher absolute values and greater variability of MWGST (Fig. 3h). It is also reflected by the correlation of the variability of MAGST and the air temperature in the both half-years with the total thickness of the seasonal snow cover on Kasprowy Wierch: δMAGST ¼ 0:949 δMWAT−0:08 δΣDSnow þ 0:539 δMSAT ðr ¼ 0:94; pb0:005Þ
ð4Þ
where: MWAT — the mean winter half-year air temperature, MSAT — the mean summer half-year air temperature, ΣDSnow — the total thickness of the seasonal snow cover. This linear regression equation explained 83% (adj r2) of the variability of this variable (Fig. 4l).
ΣDSnow ¼ 0:50 δPSnow −0:53 δPMelt −0:27 δMWAT ðr ¼ 0:88; pb0:006Þ ð1Þ
where: ΣDSnow — the total thickness of the seasonal snow cover, PSnow — snowfall, PMelt — rainfall during the melt period, MWAT — the mean winter half-year air temperature. This above equation explains 68% (adj r2) of the variability in that component of the Tatra cryosphere (Fig. 4c). 4.2.2. Lake ice cover In the analyzed 13-year-long period, the duration of the ice cover on Morskie Oko Lake was not associated/correlated with the maximum thickness of the ice on the measuring site (Fig. 4d). The number of days with the ice cover and its interannual variation depended primarily on the air temperature in winter (Fig. 4e, Eq. (2)). Also important was the impact of the thickness and duration of the snow cover expressed as the total thickness of the seasonal snow cover on Kasprowy Wierch: δNLI ¼ −0:82 δMWAT þ 0:04 δΣDSnow
ðr ¼ 0:85; pb0:003Þ
ð2Þ
where: NLI — the number of days with the lake ice cover, MWAT — the mean winter half-year air temperature, ΣDSnow — the total thickness of the seasonal snow cover. Thus, the development of the lake ice cover was also affected by rainfall and snowfall during the melt period (Eq. (1)), however, the values of the correlation coefficients did not reveal this regularity. The equation of linear regression (Eq. (2)) explained 65% (adj r2) of annual changes in the duration of the ice cover on Morskie Oko Lake (Fig. 4f). 4.2.3. Glacieret The changes in the area and front position of the Medeny glacieret, although correlated (r = 0.79; p b 0.05) were not always synchronous (Fig. 4g). In both cases the most significant were the totals of snowfall and positive degree days in the successive balance years. The changes in the area of the glacieret were far more dependent on snowfall (Fig. 4h) — especially those that had the greatest influence on the seasonal maximum of the snow cover thickness (the maximum thickness of the snow cover on Kasprowy Wierch was more important than the
4.2.5. General regularities All the components of the Tatra cryosphere indicated high sensitivity to climatic impulses. Their responses, however, varied and depended on the type of the impulse (see Section 4.2). In general, the abundance of snowfall in the winter half-year was reflected in the thickness of the snow cover and the size of the glacierets nourished by snow avalanches. The air temperature in winter and spring seasons, in turn, had a leading influence on the duration of the seasonal ice cover of the lakes and the change of permafrost under the thin snow cover. The development of the seasonal and perennial components of the cryosphere was correlated with each other (Fig. 5) and in the analyzed 13-year-long period depended primarily on meteorological conditions in the successive winter half-years. 5. Discussion The climate and cryosphere of the Tatras is characterized by high, long-term variability. The trend in the variability in the last six decades has testified to the increasing air temperature and the decreasing amount of ice in the natural environment of the region (Gądek, 2011). It was consistent with the global changes in the Earth's climate and cryosphere (e.g. IPCC, 2007; Kang et al., 2010; Dercsen et al., 2012). As presented in this paper changes of the ice deposits in the Tatra Mountains were recorded in the multi-year period which was the warmest in the functioning of the weather station at Kasprowy Wierch (Gądek and Leszkiewicz, 2012). However, all the components of the Tatra cryosphere (seasonal and perennial, surface and subsurface) were the most sensitive to the changes in the climatic conditions in the winter half-year. According to the data, the variability of the snow cover on Kasprowy Wierch is best reflected by the variability of snowfall. The air temperature has a greater influence on the snow cover on the lower-located areas, where also higher is the importance of zonal advection (Falarz, 2007). The decrease in the sensitivity of the long-term variability of the snow cover to climate changes along with the area altitude was also indicated by Beniston (1997). In this context interesting are the results of the studies on climatic conditioning the variability of the snow
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cover in the vertical profile of the Polish Tatra Mountains in the second half of the twentieth century (Falarz, 2002). At that time a correlation of the total daily thickness of the snow cover with the snowfall and air temperature was observed exclusively at the foothills of the Tatra Mountains and at the timberline, whereas at Kasprowy Wierch only snowfall was of statistical significance. The influence of the changes in the quality and abundance of precipitation (snow/rain) together with MWAT on the development of the snow cover on Kasprowy Wierch in the first decade of the twenty-first century was revealed by the equation of regression [Eq. (1)]. It may testify to the increasing importance of the contemporary changes in the air temperature for the formation of the snow cover of the Tatras. The development of the ice phenomena in Morskie Oko Lake showed a statistically significant and strong association primarily with MWAT at Kasprowy Wierch. Choiński et al. (2010) showed the dependence of the development of this lake ice cover upon the air temperature in winter and spring seasons at the foothills of the Tatra Mountains. Moreover, Choiński (2007) found that the location of the place where the lake ice cover reaches its maximum thickness is variable. This weakens the statistical relationship between the duration of the ice cover and its maximum thickness measured in only one, randomly chosen place. The variability of both of these features in the last 40-year period, however, has indicated a consistent, downward trend (e.g. Pociask-Karteczka and Choiński, 2012). It is the outcome of an increase in the air temperature in the winter half-year, which may result in a year-on-year decreasing of the thickness of so-called black ice (congelation ice) and/or acceleration of melting of the ice over during spring periods. These processes, however, are complicated by the snow cover since it: a) reduces the heat transfer between the ground and the atmosphere, b) contributes to the lowering of the ice cover under the hydrostatic water level, which in turn leads to a rapid growth of so-called white ice (slush/snow ice). Eq. (2) suggests that the decrease in the thickness of the snow cover in the Tatra Mountains strengthens the impact of climate warming on the thickness and duration of the lake ice cover. The presented fluctuations of the Medeny glacieret indicate a rapid circulation of its mass in recent years. They have been associated with concentrated snow accumulation and great ablation of snow/ice several hundred meters below the snow line. In this context, the velocity of such perennial firn-ice deposits does not really matter. In the analyzed period the Medeny glacieret reached the greatest size in 2009, whereas during the autumn of 2003 it was the smallest in nearly 180 years of its observations (Gądek and Grabiec, 2008). However, the main cause of this recession was not an extreme summer heat wave, which at that time brought enormous adverse social, economic and environmental effects in the western part of Europe (e.g. De Bono et al., 2004), but a very little amount of snow in as many as three consecutive winter seasons of 2001–2003 (Fig. 3c–e). This is also reflected in the Eq. (3), which points out that fluctuations of the glacieret in the years of 1998–2010 were more related to the variability of snow conditions (avalanche feeding) than to the variability of the air temperature, which in turn explains the frequent asynchrony of the changes in the size of the glacierets in the Tatra Mountains (Gądek, 2008). A dominant influence of the snow accumulation on the mass balance and dimensions of contemporary glacierets in the mountains of southern Europe was indicated by, inter alia, Hughes (2008) and Pecci et al. (2008). However the recession of the contemporary glacierets in this region is also linked to climate warming (e.g. Grunewald and Scheithauer, 2010; Gachev, 2011; Serrano et al., 2011). In this respect, of particular interest are the research results of Fujita et al. (2010). According to them, the correlations between the interannual variability of the glacierets ablation and summer temperature may be reduced by the variability of wind speed. The variability of permafrost in the Tatra Mountains is not monitored. Its existence, documented primarily by geophysical surveys (e.g. Mościcki and Kędzia, 2001; Dobiński et al., 2008; Gądek et al.,
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2009), may seem questionable. However, the buried ice unveiled in the Medena kotlina (Gądek and Grabiec, 2008) is a form of permafrost (Van Everdigen, 1998), and recent thermo-karst forms (Gądek and Leszkiewicz, 2012) are indicative of its degradation. These phenomena are well matched by the results of: a) GST modeling, which indicate that in the last few decades, the ground temperature on the site in the Medena kotlina has increased (Gądek and Leszkiewicz, 2012) and b) observations of the largest in the Tatra Mountains, perennial ice cover in Ice Cave in Mount Ciemniak, which, in turn, suggest that it is currently losing more mass than it has lost in previous decades (Rachlewicz and Szczuciński, 2004). The results of geophysical and microclimate measurements in the Medena kotlina has not revealed deep ventilation of the substrate, which could have been the cause of the observed there anomalies of GST (Gądek, 2012). They rather testify to the dominant role of topoclimatic conditions and the substrate structure in the spatial variation of the ground temperature, which was proved by Raska et al. (2011) in Ceske Stredohori Mts. A long-term variability of MAGST at the site in the Medena kotlina in the last 13-year-long period was mainly related to the variability of the winter half-year temperature (Eq. (4)). However, and in the past six decades, of greater importance was the substantial increase in the air temperature in the summer half-year. The significance of MSAT was also growing when the thickness and duration of the snow cover was increasing (Gądek and Leszkiewicz, 2012). Particularly important in shaping of MAGST are physical characteristics of the ground: capacity and thermal conductivity (especially thermal offset). Eqs. (1)–(4) explain from 58% to 83% of the changes of the studied components of the Tatra Mountains cryosphere in recent years. Despite the clear overall regularities in the cryosphere–climate relationships (Fig. 5), it is not always possible to properly deduce seasonal changes in the entire mountain cryosphere solely from the data on the air temperature and precipitation recorded at one reference site or the observation of one of its components. It is reflected, inter alia, in the arising sometimes discrepancies in the periods of the occurrence of extreme values of the seasonal air temperature, snowfalls and size of the individual components of the cryosphere (Fig. 3), as well as in the results of the observations and numerical modeling of the cryosphere changes (Fig. 4). A complex nature of cryospheric variables necessitates employment of various measurement methods. The selection presented in this study and the integration of optimal parameters of the main components of the non-glaciated mountain cryosphere enabled the first holistic approach to its functioning in the conditions of the changing climate. 6. Conclusions 1. All the components of the contemporary cryosphere of the Tatra Mountains are very sensitive to changes in the factors which are influential in their formation, i.e. to the changes in the air temperature in the winter half-year or in the fall/accumulation of snow. At the same time the impact of the air temperature in the summer halfyear on perennial ice deposits has increased in recent decades. 2. Generally, along with the increase of the air temperature in the Tatra Mountains, the amount of solid precipitation, and the seasonal total, maximum thickness and duration of the snow cover are getting smaller. The reduction of the winter heat loss of the atmosphere substratum results in a decrease in the thickness and duration of the lakes ice cover and permafrost degradation, whereas a reduction of the avalanche feeding induces the recession of the glacierets. The snow cover thickness affects the heat exchange between the atmosphere and the substratum, formation of slush-lake ice, and stability of the snow cover on the slope. Its variability (orographically conditioned) may diversify in time and space the reactions of the other cryosphere components to the changes in the air temperature. 3. Due to the different orographic conditions, interannual variability of the seasonal and perennial, surface and subsurface deposits of ice in
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mountain areas may not be synchronous. However, the long-term trends in this variation reflect changes in the global climate system. Acknowledgments I am grateful to anonymous reviewers and Dr. Mariusz Grabiec for their helpful comments. The study was supported by the National Science Centre (grant 2011/03/B/ST10/06115) and the University of Silesia (grant 1S-0413-001-1-01-01). References Abdel-Aziz, A.Y.I., Karara, H.M., 1971. Direct linear transformation into object space coordinates in close-range photogrammetry. American Society of Photogrammetry Symposium on Close-Range Photogrammetry, Falls Church, Virginia, USA, pp. 1–18. Barry, R.G., 2009. Mountain Weather and Climate. Cambridge University Press, Cambridge. Barry, R., Gan, T.Y., 2011. The global cryosphere. Past, Present, and Future Cambridge University Press, Cambridge. Barry, R.G., Jania, J., Birkenmajer, K., 2011. Dobrowolski — the first cryospheric scientist — and the subsequent development of cryospheric science. Hist. Geo Space Sci. 2, 75–79. Baumgart-Kotarba, M., Kotarba, A., 2001. Deglaciation of the Sucha Woda and Pańszczyca valleys in the Polish High Tatras. Stud. Geomorphol. Carpatho-Balc. 35, 7–38. Beniston, M., 1997. Variations of snow cover depth and duration in the Swiss Alps over the last 50 years: links changes in large-scale climatic forcings. Clim. Chang. 36, 281–300. Choiński, A., 2007. Zjawiska lodowe na Morskim Oku w Tatrach. Folia Geogr. Ser. Geogr. Phys. 37–38, 65–77. Choiński, A., Kolendowicz, L., Pociask-Karteczka, J., Sobkowiak, L., 2010. Changes in lake ice cover on the Morskie Oko Lake in Poland (1971–2007). Adv. Clim. Chang. Res. 1 (2), 71–75. De Bono, A., Peduzzi, P., Kluser, S., Giuliani, G., 2004. Impacts of summer 2003 heat wave in Europe. Environment Alert Bulletin, 2. UNEP. Dercsen, C., Smith, S.L., Sharp, M., Brown, L., Howell, S., Copland, L., Mueller, D.R., Gauthier, Y., Fletcher, C.G., Tivy, A., Bernier, M., Bourgeois, J., Brown, R., Burn, C.R., Duguay, C., Kushner, P., Langlois, A., Lewkowicz, A.G., Royer, A., Walker, A., 2012. Variability and change in the Canadian cryosphere. Clim. Chang. http://dx.doi.org/10.1007/ s10584-012-0470-0. Dobiński, W., 2005. Permafrost of the Carpathian and Balkan Mountains, eastern and southeastern Europe. Permafr. Periglac. Process. 16, 395–398. Dobiński, W., Żogała, B., Wziętek, K., Litwin, L., 2008. Results of geophysical surveys on Kasprowy Wierch, the Tatra Mountains, Poland. In: Hauck, C., Kneisel, C. (Eds.), Applied Geophysics in Periglacial Environments. Cambridge University Press, Cambridge, pp. 126–136. Dobrowolski, B., 1923. Historja naturalna lodu. Kasa Pomocy im. Dr J. Mianowskiego, Warszawa. Falarz, M., 2002. Klimatyczne przyczyny zmian i wieloletniej zmienności występowania pokrywy śnieżnej w polskich Tatrach. Prz. Geogr. 74 (1), 83–106. Falarz, M., 2007. Snow cover variability in Poland in relation to the macro- and mesoscale atmospheric circulation in the twentieth century. Int. J. Climatol. 27, 2069–2081. Fujita, K., Hiyama, K., Iida, H., Ageta, Y., 2010. Self‐regulated fluctuations in the ablation of a snow patch over four decades. Water Resour. Res. 46, W11541. Gachev, E., 2011. Inter-annual size variations of Snezhnika glacieret (the Pirin Mountains, Bulgaria) in the last ten years. Stud. Geomorphol. Carpatho-Balc. 45, 7–19. Gądek, B., 2008. The problem of firn-ice patches in the Polish Tatras as an indicators of climatic fluctuations. Geogr. Pol. 81, 10–25. Gądek, B., 2011. Wieloletnia zmienność kriosfery Tatr. Czasopismo Geogr. 82 (4), 371–385. Gądek, B., 2012. Debris slopes ventilation in the periglacial zone of the Tatra Mountains (Poland and Slovakia): the indicators. Cold Reg. Sci. Technol. 74–75, 1–10. Gądek, B., Grabiec, M., 2008. Glacial ice and permafrost distribution in the Medena kotlina (Slovak Tatras): mapped with application of GPR and GST measurements. Stud. Geomorphol. Carpatho-Balc. 42, 5–22. Gądek, B., Leszkiewicz, J., 2012. Impact of climate warming on the ground surface temperature in the sporadic permafrost zone of the Tatra Mountains, Poland and Slovakia. Cold Reg. Sci. Technol. 79–80, 75–83.
Gądek, B., Rączkowska, Z., Żogała, B., 2009. Debris slope morphodynamics as an permafrost indicator in its sporadic occurrence zone, High Tatra Mts., Slovakia. Z. Geomorphol. 53 (2), 79–100. Grunewald, K., Scheithauer, J., 2010. Europe's southernmost glaciers: response and adaptation to climate change. J. Glaciol. 59 (195), 129–142. Haeberli, W., 1998. Historical evolution and operational aspects of worldwide glacier monitoring. UNESCO Stud. Rep. Hydrol. 56, 35–51. Hess, M., 1996. Klimat. In: Mirek, Z. (Ed.), Przyroda Tatrzańskiego Parku Narodowego. TPN, Kraków-Zakopane, pp. 53–69. Hughes, T.J., 1998. Ice Sheets. Oxford University Press, New York. Hughes, P.D., 2008. Response of a Montenegro glacier to extreme summer heat waves in 2003 and 2007. Geogr. Ann. 90A (4), 259–267. IPCC, 2007. Climate Change: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge. Jania, J., 1997. The problem of Holocene glacier and snow patches fluctuations in the Tatra Mountains: a short report. In: Frenzel, B., Boulton, G.S., Glaser, B., Huchriede, U. (Eds.), Glacial fluctuations during the Holocene. Jena, Gustav Fischer, Palaoklimaforschung, 24, pp. 85–93. Kang, S., Xu, Y., You, Q., Flugel, W.A., Pepin, P., Yao, T., 2010. Review of climate and cryospheric change in the Tibetan Plateau. Environ. Res. Lett. 5, 1–8. Lindner, L., Dzierżek, J., Marciniak, B., Nitychoruk, J., 2003. Outline of quaternary glaciations in the Tatra Mts.: their development, age and limits. Geol. Q. 44, 269–280. López-Moreno, J.I., 2005. Recent variations of snowpack depth in the Central Spanish Pyrenees. Arct. Antarct. Alp. Res. 37 (2), 253–260. López-Moreno, J.I., Vicente-Serrano, S.M., 2007. Atmospheric circulation influence on the interannual variability of snow pack in the Spanish Pyrenees during the second half of the 20th century. Nord. Hydrol. 38 (1), 33–44. Makos, M., Nitychoruk, J., 2011. Last Glacial Maximum climatic conditions in the Polish part of the High Tatra Mountains (Western Carpathians). Geol. Q. 55 (3), 253–268. Mościcki, J., Kędzia, S., 2001. Investigation of mountain permafrost in the Kozia Dolinka Valley, Tatra Mountains, Poland. Nor. Geogr. Tidsskr. 55, 235–240. Niedźwiedź, T., 1992. Climate of the Tatra Mountains. Mountain Research and Development 12, 131–146. Pacl, J., Wit-Jóźwikowa, K., 1974. Teplota vod. In: Konček, M. (Ed.), Klima Tatier, Veda, Bratislava, pp. 181–204. Pecci, M., D'Agata, C., Smiraglia, C., 2008. Ghiacciaio del Calderone (Apennines, Italy): the mass balance of a shrinking Mediterranean glacier. Geogr. Fis. Din. Quat. 31, 55–62. Pociask-Karteczka, J., Choiński, A., 2012. Recent trends in ice cover duration for Lake Morskie Oko (Tatra Mountains, East-Central Europe). Hydrol. Res. 43 (4), 500–506. Rachlewicz, G., Szczuciński, W., 2004. Seasonal and decadal ice mass balance change in the ice cave Jaskinia Lodowa w Ciemniaku, the Tatra Mountains, Poland. Theor. Appl. Karstol. 17, 11–18. Rączkowska, Z., 2007. Współczesna rzeźba peryglacjalna wysokich gór Europy. Polska Akademia Nauk, Instytut Geografii i Przestrzennego Zagospodarowania, Prace Geograficzne, 212, Warszawa. Raska, P., Kirchner, K., Raska, M., 2011. Winter microclimatic regime of low-altitude scree slopes and its relation to topography: case study from the Ceske Stredohori Mts. (N Czech Republic). Geogr. Fis. Din. Quat. 34, 235–246. Serrano, E., González-Trueba, J.J., Sanjosé, J.J., Del Río, L.M., 2011. Ice patch origin, evolution and dynamics in a temperate high mountain environment: the Jou Negro, Picos de Europa (NW Spain). Geogr. Ann. 93, 57–70. Siarzewski, W., 1994. Jaskinia Lodowa w Ciemniaku. In: Grodzicki, J. (Ed.), Jaskinie Tatrzańskiego Parku Narodowego, 5. PTPNoZ, TPN, Warszawa, pp. 142–153. Van Everdigen, R.O. (Ed.), 1998. Definitions, Multi-Language Glossary of Permafrost and Related Ground-Ice Terms. International Permafrost Association, the University of Calgary, Calgary. Voigt, T., Füssel, H.-M., Gärtner-Roer, I., Huggel, Ch., Marty, Ch., Zemp, M., 2010. Impacts of climate change on snow, ice, and permafrost in Europe: observed trends, future projections, and socio-economic relevance. ETC/ACC Technical Paper 2010/13. Zasadni, J., Kłapyta, P., 2009. An attempt to assess the modern and Little Ice Age climatic snowline altitude in the Tatra Mountains. Landf. Anal. 10, 124–133. Zemp, M., Paul, F., Hoelzle, M., Haeberli, W., 2008. Glacier fluctuations in the European Alps 1850–2000: an overview and spatio-temporal analysis of available data. In: Orlove, B., Wiegandt, E., Luckmann, B. (Eds.), The Darkening Peaks: Glacial Retreat in Scientific and Social Context. University of California Press, pp. 152–167. Żmudzka, E., 2011. Contemporary climate changes in the high mountain part of the Tatras. Misc. Geogr. 15, 93–102.
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Global and Planetary Change journal homepage: www.elsevier.com/locate/gloplacha
Climatic sensitivity of the non-glaciated mountains cryosphere (Tatra Mts., Poland and Slovakia) Bogdan Gądek Department of Geomorphology, University of Silesia, Sosnowiec, Poland
a r t i c l e
i n f o
Article history: Received 21 July 2013 Received in revised form 18 June 2014 Accepted 1 July 2014 Available online 5 July 2014 Keywords: mountain cryosphere snow cover lake ice glacierets sporadic permafrost the Tatra Mountains
a b s t r a c t This paper concerns the response of the conditioned by orography cryosphere of the non-glaciated mountains of mid-latitude to the climate impulses. It presents the relationships among the air temperature, precipitation, snow cover, lake ice cover, firn-ice patches (glacierets) and permafrost in the Tatras. The data from the warmest multiyear in the history of the local meteorological measurements and statistical models (multiple regression) have been used. The results indicate that all the components of the contemporary cryosphere are very sensitive to the changes in the air temperature in winter or snow precipitation/accumulation. Due to the diverse orographic conditions, interannual variability of seasonal and perennial, surface and subsurface ice deposits in the mountain areas may not be synchronous. However, the long-term trends of this variability reflect the changes in the global climate system. © 2014 Elsevier B.V. All rights reserved.
1. Introduction The Earth's coating containing ice extends from the upper troposphere to the lower boundary of permafrost. Dobrowolski (1923) called it the cryosphere (from Greek κρύος — ice, frost) (Barry et al., 2011). It is an integral part of the climate system. Changes in the ice mass occurring in the Earth's environment are related to the transfers of energy and humidity between the atmosphere, hydrosphere and lithosphere. The accompanying feedback, in turn, affects the atmospheric and oceanic circulation (Barry and Gan, 2011). The main components of the cryosphere include cloud ice, snow, glaciers, ice caps and ice fields, ice sheets, the ice cover of the seas, lakes and rivers, and ice in the ground. They are different in terms of the place of occurrence, the role in the natural environment and the sensitivity to climate change. According to what geological and geomorphological data indicate, the changes in Earth's cryosphere occur in cycles of variable length. The contemporary phase of these changes is evidenced by the results of terrestrial and remote sensing monitoring of the main components of the cryosphere (e.g. IPCC, 2007). The noted decline in the mass of ice in the Earth's environment is a continuation of the global changes which began about 20,000–18,000 years ago (e.g. Hughes, 1998). In many mountains glaciated during the Pleistocene, the climatic snow line (CSL) nowadays runs over the highest peaks, and the only traces of the past glaciers are of the geomorphological nature. The results of the international monitoring of glaciers (Haeberli, 1998), carried out
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since 1894, reflect a further moving upward of the CSL and the subsequent deglaciation of the mountain areas (e.g. Zemp et al., 2008). The retreat of glaciers, however, facilitated the development of the periglacial components of the cryosphere. In the natural environment of the several, glaciated in the past mountains of mid-latitude, ice presently occurs not only seasonally but also perennially, both on and below the surface of the terrain. The relief affects the local radiation balance, the air circulation and precipitation patterns (Barry, 2009) and may facilitate the concentrated accumulation of snow and/or cold, which may result in respectively firn-ice patches (glacierets) and patches of permafrost. Because of a low temperature of ice melting, the recession of the cryosphere components is usually considered as the result of global warming. However, in the mountain environment, the relief, as a stable component of the climate system, may locally suppress the impact of global warming on the rate of ice melting. Moreover, a decrease in the occurrence duration and thickness of snow cover may also happen in consequence of a decrease in snowfall (e.g. López-Moreno, 2005; López-Moreno and Vicente-Serrano, 2007; Żmudzka, 2011). This may result in the recession of glacierets simultaneous with the aggradation of permafrost — regardless of the changes in the air temperature (Gądek, 2008; Gądek and Leszkiewicz, 2012). The cryosphere is not merely a collection of the ice components of the natural environment but it is an open, dynamic and complex system, which is characterized by the mass circulation and the associated energy, and which both responds to external impulses and impacts upon the environment. However, in the literature there is a lack of comprehensive studies on the functioning of the cryosphere of non-glaciated mountains, even though the changes are due to the current weather conditions (Fig. 1).
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The climate is sufficiently severe for the middle periglacial belt to be present above the upper timberline (Rączkowska, 2007). Sporadic and discontinuous permafrost may occur above 1700 m a.s.l. (Dobiński, 2005), but caves where ice masses are permanent are located above 1200 m a.s.l. (Siarzewski, 1994). In the second half of the twentieth century and in the first decade of the twenty-first century in the Tatra Mountains there was registered a decrease in the number of days with snow cover and in the maximum thickness of the snow cover, shortening of the duration and a reduction of the thickness of the lakes' ice cover, a considerable or total exchange of the glaciarets' mass, and degradation of the patches of permafrost. These changes were consistent with an increase in the air temperature in winter and summer seasons, and with a decrease in snowfall (Gądek, 2011). 3. Data and methods 3.1. Air temperature, precipitation and snow cover data
Fig. 1. The hierarchical model of relationships between climate and cryosphere in nonglaciated mountains.
The first such attempt has been made in this work. Its aim is to explore the statistical relationships among a long-term variability of the snow cover, lake ice, glacierets, permafrost, precipitation and the air temperature above the timberline in the Tatra Mountains for a better understanding of the processes that control the behavior of the contemporary mountain cryosphere. The study area belongs to the international network of biosphere reserves (UNESCO). It rises between the lower limit of sporadic permafrost (Dobiński, 2005) and CSL (Zasadni and Kłapyta, 2009) and is included in the group of important ice and snow regions in Europe (Voigt et al., 2010). The characteristics of the natural environment of the Tatra Mountains, the observational data on their variability since the Little Ice Age, and a well-developed infrastructure which has been providing a continuous service for climatologic research for decades — all of these predispose these mountains to the role of the reference area for monitoring global climate changes and their geoecological implications. 2. Regional setting The Tatra Mountains are the highest range in the Carpathians arc (Gerlach summit: 2655 m a.s.l.), and also the highest non-glaciated mountains between the European Alps, the Scandes and the Caucasus (Fig. 2). The cold periods of the Pleistocene caused several mountain glaciations (Baumgart-Kotarba and Kotarba, 2001; Lindner et al., 2003). The equilibrium line altitude (ELA; ≈ CSL) of Würmian glaciers during the period of their maximum range probably was about 1500 m a.s.l. (Makos and Nitychoruk, 2011). Currently, this altitude constitutes the upper timberline, while the contemporary CSL is located more than 1000 m above (Zasadni and Kłapyta, 2009). The orographic snow line at the northern side of the Tatras is delimited by firn-ice patches nourished by snow avalanches, down to 1530 m a.s.l. (e.g. Jania, 1997; Gądek, 2008). The present-day climate is transitional between maritime and continental influences. The mean annual air temperature (MAAT) at the northern and southern Tatras' foothills (ca. 850 m a.s.l.) is 6 °C and 8 °C respectively. In the highest summits (above 2600 m a.s.l.) MAAT is −4 °C (Hess, 1996). The mean total precipitation ranges from 1100 mm in the north foothills to 1900 mm in higher parts (Niedźwiedź, 1992) and the number of days with snow cover ranges from about 100 to 290 respectively (Hess, 1996). The ice cover on the lakes of the Tatras usually remains for 6 to 10 months. Sometimes, however, on the uppermost lakes (above 2000 m a.s.l.) it persisted throughout the year (e.g. Pacl and Wit-Jóźwikowa, 1974).
Daily values of the air temperature, precipitation and snow depth from the synoptic station located at the top of Kasprowy Wierch Mountain (WMO id: 12650) were applied. This meteorological station is the highest in Poland (1991 m a.s.l.) and the only one in the alpine zone of the Tatras (Fig. 2). The data were derived from the Global Historical Climatology Network accessible from the NOAA website. They included the hydrological years (October–September) of 1998–2010. The daily air temperature values were the bases for the calculation of the mean annual, winter and summer half-year air temperature (MAAT, MWAT and MSAT respectively), mean values of the winter (December– February), spring (March–May), summer (June–August), autumn (September–November) temperature and totals of positive degree days (PDD) in subsequent years. The daily precipitation totals were used to determine total annual and semi-annual precipitation, and total precipitation in the time of the increased snow cover (snowfall) and during the melt. However, the daily snow depth values were used to calculate the number of days with snow cover of ≥1 cm, as well as the seasonal maximum and total of the daily snow depth. 3.2. Lake ice cover, glacieret and permafrost data All the data refers to the hydrological years of 1998–2010. The analysis was focused on the duration and seasonal maximum thickness of the ice cover of Morskie Oko Lake (the data from the Institute of Meteorology and Water Management). This is the largest lake in the Tatras. It is located at an altitude of 1395 m a.s.l., it has the area of about 349,400 m2 and the capacity of approximately 9,935,000 m3 (Choiński et al., 2010). Photogrammetric methods were used to acquire data about the area and front altitude of the Medeny glacieret at the end of the ablation seasons. Each year stereoscopic images of the glacieret were taken with a non-metric camera, then they were calibrated with the method of direct linear transformation (Abdel-Aziz and Karara, 1971) and digitized using a digital analytical autograph. The Medeny glacieret is the largest, contemporary, perennial ice form in the Tatras, occurring on the surface of the area. It is located at an altitude of 2050 m a.s.l., at the place of N exposure (Fig. 2). The temperature of the active layer and permafrost in the Tatra Mountains are not monitored, and the measurement of the ground surface temperature (GST) in these areas have started only recently. Therefore the results of the statistical modeling of average GST values in consecutive years, winter and summer half-year (MAGST, MWGST and MSGST respectively) in the Medena kotlina were used for that purpose (Gądek and Leszkiewicz, 2012). This is the only place in the Carpathian Mountains where the permafrost existence has been evidenced not only with geophysical methods (GST, GPR, electromagnetic and DC resistivity measurement), but also outcrop of buried massive ice
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Fig. 2. Location of the investigation areas: I — Kasprowy Wierch Mt. (photo by W. Kaszkin), II — Morskie Oko Lake (photo by R.J. Kaczka), III — the Medena kotlina Valley (IIIa — the Medeny glacieret, IIIb — outcrop of buried massive ice).
have been found, and its development monitored together with morphodynamics of the slope (Gądek and Grabiec, 2008; Gądek et al., 2009).
the dependent variable with making allowance for the number of used independent variables. 4. Results
3.3. Statistical methods In order to examine the sensitivity of the individual elements of the Tatras' cryosphere to the changes in the air temperature and precipitation, the methods of descriptive statistics, correlation and multiple regression are applied. Firstly, minimum and maximum values, arithmetic means with standard errors and standard deviations of all the data on temperature, precipitation and cryosphere were determined. The year-on-year changes in the variables have been calculated, and their distribution tested. Then, the analyzed data were standardized and put through the cross-correlation (Pearson and Spearman) together with checking its statistical significance with the t test. Basing on the disclosed correlations (the level of significance α ≤ 0.05) the equation of multiple linear regression has been developed (with the method of least squares) to describe the relationship between the variability of individual cryosphere components and the air temperature or/and precipitation. In each case, there have been calculated: the coefficient of correlation (r), the level of statistical significance (p), and the adjusted coefficient of determination (adj r2), which indicates to what degree the statistical model (regression equation) explains the variability of
The changes in the air temperature, precipitation, snow cover, lake ice, glacieret and GST at the permafrost site registered in the mountains in the years of 1998–2010, are illustrated in Fig. 3, whereas the correlation between these components of the climate and cryosphere are presented in Figs. 4 and 5. 4.1. Variability of the climate and cryosphere components 4.1.1. Variability of the climate components In the analyzed period, MAAT at Kasprowy Wierch varied from − 0.63 °C (in 2004) to 1.06 °C (in 2007). The values of arithmetic mean (± standard error) and standard deviation were respectively: −0.03 (±0.13) °C and 0.46 °C. In 2004, extremely low values of MSAT and the amount of the PDD were recorded, whereas the coldest spring, summer and autumn occurred in 1998, the coldest winter — in 2010. The coldest winter half-year was in 2005 and 2006. In 2007, the winter half-year was unusually warm (both winter and spring), while the summer was only about 0.2 °C cooler than the warmest summer in 2002. The warmest summer half-year, however, was in 2000, when the
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Fig. 3. Variability of the climate and cryosphere components in the Tatra Mountains.
largest amount of the PDD and the average temperature of the autumn. In 2004 and 2007, the greatest changes in the year-on-year air temperature were noted. In the first case, the values of MSAT, summer temperature and total PDD decreased respectively by 1.28 °C d, 2.06 °C d and 202.5 °C d, while in the second case the values of MAAT and MSAT increased respectively by 2.26 °C and 2.7 °C (Fig. 3a–b). The total annual precipitation in the period of the analyzed 13 years was changing from 1373 mm (in 2003) to 2340 mm (in 2001). The arithmetic mean and standard deviation were as follows: 1756 (±74.21) mm and 267 mm. In the year 2003, precipitation was particularly low during the development of the snow cover. However, the lowest amounts of precipitation in the winter and summer half-year were reported in 2006 and 1999 respectively. In the winter half-year of 2006 an exceptionally large year-on-year change in total precipitation (a decline by 239 mm), while the biggest change of total snowfall occurred in 1999 (an increase by 466 mm). However, in the summer half-year of 2001 an extreme increase in precipitation was registered. The total was up to 740 mm higher than in the previous year. The highest precipitation in the winter half-year, including snowfall, occurred in 1998 (Fig. 3c–d).
4.1.2. Variability of the cryosphere components The number of days with the snow cover on Kasprowy Wierch Mountain ranged from 199 (in 2009) to 268 (in 1999). The maximum thickness of the snow cover was changing at that time from 140 cm to 325 cm reaching extreme values in two consecutive winter seasons in 2001 and 2000. In the same seasons the minimum and maximum totals of daily snow cover thickness were recorded (Fig. 3e). They amounted to 10,840 cm d and 30,693 cm d respectively. The mean thirteen-year-old value of the total of the seasonal snow cover thickness was 21,259.5 (±1608.5) cm d, and the standard deviation was equal to 5799.5 cm d. The ice cover of Morskie Oko Lake was formed in the months of November–December, and disappeared in the months of April–May. The duration of the total icing ranged from 112 days (in 2001) to 172 days (in 2006). The maximum seasonal thickness of the ice at the monitored site varied from 40 cm (in 2000) to 114 cm (in 2008). The mean values of these parameters of the ice cover amounted to 140 (±5) days and 60.38 (±5.88) cm whereas the standard deviations — 19 days and 21.19 cm. The biggest year-on-year changes in the number of days with the ice cover were registered in 2007 (a decrease by
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Fig. 4. The relationships between interannual variability of the Tatra Mountains cryosphere components, their climatic sensitivity and results of statistical modeling (standardized data).
49 days) and 1999 (an increase by 43 days), and in the maximum thickness of the ice in 2008 (an increase by 50 cm) and 2010 (a decrease by 41 cm) (Fig. 3f). The area of the Medeny glacieret in autumn seasons varied from 12,400 m2 (in 2003) to 28,100 m2 (in 2009). The arithmetic mean and standard deviation were 21,500 (±1200) m2 and 4300 m2 respectively. By 2003 the glacieret had been in clear recession, then quickly reached the size equal to that of the end of the 90s of the twentieth century. The biggest changes in its area took place in 1999 (it decreased by 9000 m2) and 2004 (increased by 8900 m2). The year 2004 saw a record-breaking change in the position of the front of the glacieret. Its range increased then by 88 m (Fig. 3g). The results of statistical modeling indicate that in the Medena kotlina at the site of permafrost occurrence MAGST varied from −0.58 °C (in 2004) to 0.27 °C (2001 and 2007). The arithmetic mean
and standard deviation were −0.27 (±0.07)°C and 0.25 °C respectively. MWGST ranged from − 4.9 °C (in 2006) to − 3.3 °C (in 2007). The change of the average GST in the two winter half-years was record high, whereas the minimum and maximum MSGST amounted to 3.13 °C (in 2004) and 4.47 °C (in 2000). Both of these values were extremely different from the average GST of the previous summer half-year (Fig. 3h). 4.2. Climatic sensitivity of the cryosphere components 4.2.1. Snow cover The most comprehensive index of how snowy the winter is — the total thickness of the seasonal snow cover — depends on the duration of the snow cover and its daily thickness. In the analyzed period, the value of this ratio depended mainly on the thickness of the snow
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total of its daily thickness). This relationship is demonstrated by the equation: δAreaGlac ¼ 0:45 δDMax
Sn −0:54
δΣPDD ðr ¼ 0:81; pb0:008Þ
ð3Þ
where: AreaGlac — the area of the glacieret, DMax Sn — the seasonal maximum of the snow cover thickness, ΣPDD — the total of positive degree days. Model (3) explained 58% (adj r2) of the variability of the described variable (Fig. 4i).
Fig. 5. The relationships between interannual variability of seasonal and perennial components of the Tatra Mountains cryosphere (standardized data).
cover (Fig. 4a). The number of days with the snow cover was of lesser importance. Interannual changes in the total thickness of the seasonal snow cover on Kasprowy Wierch were primarily associated with the changes in the amount of snowfall. Moreover, statistically significant was also the effect of rainfall during the snow-melt period and the air temperature in the winter (Fig. 4b). This correlation is illustrated by the linear regression:
4.2.4. Permafrost In the Medena kotlina, at the site of permafrost occurrence, MAGST was more influenced by the temperature of the ground in the winter half-year than in the summer half-year (Fig. 4j–k). It was the result of the higher absolute values and greater variability of MWGST (Fig. 3h). It is also reflected by the correlation of the variability of MAGST and the air temperature in the both half-years with the total thickness of the seasonal snow cover on Kasprowy Wierch: δMAGST ¼ 0:949 δMWAT−0:08 δΣDSnow þ 0:539 δMSAT ðr ¼ 0:94; pb0:005Þ
ð4Þ
where: MWAT — the mean winter half-year air temperature, MSAT — the mean summer half-year air temperature, ΣDSnow — the total thickness of the seasonal snow cover. This linear regression equation explained 83% (adj r2) of the variability of this variable (Fig. 4l).
ΣDSnow ¼ 0:50 δPSnow −0:53 δPMelt −0:27 δMWAT ðr ¼ 0:88; pb0:006Þ ð1Þ
where: ΣDSnow — the total thickness of the seasonal snow cover, PSnow — snowfall, PMelt — rainfall during the melt period, MWAT — the mean winter half-year air temperature. This above equation explains 68% (adj r2) of the variability in that component of the Tatra cryosphere (Fig. 4c). 4.2.2. Lake ice cover In the analyzed 13-year-long period, the duration of the ice cover on Morskie Oko Lake was not associated/correlated with the maximum thickness of the ice on the measuring site (Fig. 4d). The number of days with the ice cover and its interannual variation depended primarily on the air temperature in winter (Fig. 4e, Eq. (2)). Also important was the impact of the thickness and duration of the snow cover expressed as the total thickness of the seasonal snow cover on Kasprowy Wierch: δNLI ¼ −0:82 δMWAT þ 0:04 δΣDSnow
ðr ¼ 0:85; pb0:003Þ
ð2Þ
where: NLI — the number of days with the lake ice cover, MWAT — the mean winter half-year air temperature, ΣDSnow — the total thickness of the seasonal snow cover. Thus, the development of the lake ice cover was also affected by rainfall and snowfall during the melt period (Eq. (1)), however, the values of the correlation coefficients did not reveal this regularity. The equation of linear regression (Eq. (2)) explained 65% (adj r2) of annual changes in the duration of the ice cover on Morskie Oko Lake (Fig. 4f). 4.2.3. Glacieret The changes in the area and front position of the Medeny glacieret, although correlated (r = 0.79; p b 0.05) were not always synchronous (Fig. 4g). In both cases the most significant were the totals of snowfall and positive degree days in the successive balance years. The changes in the area of the glacieret were far more dependent on snowfall (Fig. 4h) — especially those that had the greatest influence on the seasonal maximum of the snow cover thickness (the maximum thickness of the snow cover on Kasprowy Wierch was more important than the
4.2.5. General regularities All the components of the Tatra cryosphere indicated high sensitivity to climatic impulses. Their responses, however, varied and depended on the type of the impulse (see Section 4.2). In general, the abundance of snowfall in the winter half-year was reflected in the thickness of the snow cover and the size of the glacierets nourished by snow avalanches. The air temperature in winter and spring seasons, in turn, had a leading influence on the duration of the seasonal ice cover of the lakes and the change of permafrost under the thin snow cover. The development of the seasonal and perennial components of the cryosphere was correlated with each other (Fig. 5) and in the analyzed 13-year-long period depended primarily on meteorological conditions in the successive winter half-years. 5. Discussion The climate and cryosphere of the Tatras is characterized by high, long-term variability. The trend in the variability in the last six decades has testified to the increasing air temperature and the decreasing amount of ice in the natural environment of the region (Gądek, 2011). It was consistent with the global changes in the Earth's climate and cryosphere (e.g. IPCC, 2007; Kang et al., 2010; Dercsen et al., 2012). As presented in this paper changes of the ice deposits in the Tatra Mountains were recorded in the multi-year period which was the warmest in the functioning of the weather station at Kasprowy Wierch (Gądek and Leszkiewicz, 2012). However, all the components of the Tatra cryosphere (seasonal and perennial, surface and subsurface) were the most sensitive to the changes in the climatic conditions in the winter half-year. According to the data, the variability of the snow cover on Kasprowy Wierch is best reflected by the variability of snowfall. The air temperature has a greater influence on the snow cover on the lower-located areas, where also higher is the importance of zonal advection (Falarz, 2007). The decrease in the sensitivity of the long-term variability of the snow cover to climate changes along with the area altitude was also indicated by Beniston (1997). In this context interesting are the results of the studies on climatic conditioning the variability of the snow
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cover in the vertical profile of the Polish Tatra Mountains in the second half of the twentieth century (Falarz, 2002). At that time a correlation of the total daily thickness of the snow cover with the snowfall and air temperature was observed exclusively at the foothills of the Tatra Mountains and at the timberline, whereas at Kasprowy Wierch only snowfall was of statistical significance. The influence of the changes in the quality and abundance of precipitation (snow/rain) together with MWAT on the development of the snow cover on Kasprowy Wierch in the first decade of the twenty-first century was revealed by the equation of regression [Eq. (1)]. It may testify to the increasing importance of the contemporary changes in the air temperature for the formation of the snow cover of the Tatras. The development of the ice phenomena in Morskie Oko Lake showed a statistically significant and strong association primarily with MWAT at Kasprowy Wierch. Choiński et al. (2010) showed the dependence of the development of this lake ice cover upon the air temperature in winter and spring seasons at the foothills of the Tatra Mountains. Moreover, Choiński (2007) found that the location of the place where the lake ice cover reaches its maximum thickness is variable. This weakens the statistical relationship between the duration of the ice cover and its maximum thickness measured in only one, randomly chosen place. The variability of both of these features in the last 40-year period, however, has indicated a consistent, downward trend (e.g. Pociask-Karteczka and Choiński, 2012). It is the outcome of an increase in the air temperature in the winter half-year, which may result in a year-on-year decreasing of the thickness of so-called black ice (congelation ice) and/or acceleration of melting of the ice over during spring periods. These processes, however, are complicated by the snow cover since it: a) reduces the heat transfer between the ground and the atmosphere, b) contributes to the lowering of the ice cover under the hydrostatic water level, which in turn leads to a rapid growth of so-called white ice (slush/snow ice). Eq. (2) suggests that the decrease in the thickness of the snow cover in the Tatra Mountains strengthens the impact of climate warming on the thickness and duration of the lake ice cover. The presented fluctuations of the Medeny glacieret indicate a rapid circulation of its mass in recent years. They have been associated with concentrated snow accumulation and great ablation of snow/ice several hundred meters below the snow line. In this context, the velocity of such perennial firn-ice deposits does not really matter. In the analyzed period the Medeny glacieret reached the greatest size in 2009, whereas during the autumn of 2003 it was the smallest in nearly 180 years of its observations (Gądek and Grabiec, 2008). However, the main cause of this recession was not an extreme summer heat wave, which at that time brought enormous adverse social, economic and environmental effects in the western part of Europe (e.g. De Bono et al., 2004), but a very little amount of snow in as many as three consecutive winter seasons of 2001–2003 (Fig. 3c–e). This is also reflected in the Eq. (3), which points out that fluctuations of the glacieret in the years of 1998–2010 were more related to the variability of snow conditions (avalanche feeding) than to the variability of the air temperature, which in turn explains the frequent asynchrony of the changes in the size of the glacierets in the Tatra Mountains (Gądek, 2008). A dominant influence of the snow accumulation on the mass balance and dimensions of contemporary glacierets in the mountains of southern Europe was indicated by, inter alia, Hughes (2008) and Pecci et al. (2008). However the recession of the contemporary glacierets in this region is also linked to climate warming (e.g. Grunewald and Scheithauer, 2010; Gachev, 2011; Serrano et al., 2011). In this respect, of particular interest are the research results of Fujita et al. (2010). According to them, the correlations between the interannual variability of the glacierets ablation and summer temperature may be reduced by the variability of wind speed. The variability of permafrost in the Tatra Mountains is not monitored. Its existence, documented primarily by geophysical surveys (e.g. Mościcki and Kędzia, 2001; Dobiński et al., 2008; Gądek et al.,
7
2009), may seem questionable. However, the buried ice unveiled in the Medena kotlina (Gądek and Grabiec, 2008) is a form of permafrost (Van Everdigen, 1998), and recent thermo-karst forms (Gądek and Leszkiewicz, 2012) are indicative of its degradation. These phenomena are well matched by the results of: a) GST modeling, which indicate that in the last few decades, the ground temperature on the site in the Medena kotlina has increased (Gądek and Leszkiewicz, 2012) and b) observations of the largest in the Tatra Mountains, perennial ice cover in Ice Cave in Mount Ciemniak, which, in turn, suggest that it is currently losing more mass than it has lost in previous decades (Rachlewicz and Szczuciński, 2004). The results of geophysical and microclimate measurements in the Medena kotlina has not revealed deep ventilation of the substrate, which could have been the cause of the observed there anomalies of GST (Gądek, 2012). They rather testify to the dominant role of topoclimatic conditions and the substrate structure in the spatial variation of the ground temperature, which was proved by Raska et al. (2011) in Ceske Stredohori Mts. A long-term variability of MAGST at the site in the Medena kotlina in the last 13-year-long period was mainly related to the variability of the winter half-year temperature (Eq. (4)). However, and in the past six decades, of greater importance was the substantial increase in the air temperature in the summer half-year. The significance of MSAT was also growing when the thickness and duration of the snow cover was increasing (Gądek and Leszkiewicz, 2012). Particularly important in shaping of MAGST are physical characteristics of the ground: capacity and thermal conductivity (especially thermal offset). Eqs. (1)–(4) explain from 58% to 83% of the changes of the studied components of the Tatra Mountains cryosphere in recent years. Despite the clear overall regularities in the cryosphere–climate relationships (Fig. 5), it is not always possible to properly deduce seasonal changes in the entire mountain cryosphere solely from the data on the air temperature and precipitation recorded at one reference site or the observation of one of its components. It is reflected, inter alia, in the arising sometimes discrepancies in the periods of the occurrence of extreme values of the seasonal air temperature, snowfalls and size of the individual components of the cryosphere (Fig. 3), as well as in the results of the observations and numerical modeling of the cryosphere changes (Fig. 4). A complex nature of cryospheric variables necessitates employment of various measurement methods. The selection presented in this study and the integration of optimal parameters of the main components of the non-glaciated mountain cryosphere enabled the first holistic approach to its functioning in the conditions of the changing climate. 6. Conclusions 1. All the components of the contemporary cryosphere of the Tatra Mountains are very sensitive to changes in the factors which are influential in their formation, i.e. to the changes in the air temperature in the winter half-year or in the fall/accumulation of snow. At the same time the impact of the air temperature in the summer halfyear on perennial ice deposits has increased in recent decades. 2. Generally, along with the increase of the air temperature in the Tatra Mountains, the amount of solid precipitation, and the seasonal total, maximum thickness and duration of the snow cover are getting smaller. The reduction of the winter heat loss of the atmosphere substratum results in a decrease in the thickness and duration of the lakes ice cover and permafrost degradation, whereas a reduction of the avalanche feeding induces the recession of the glacierets. The snow cover thickness affects the heat exchange between the atmosphere and the substratum, formation of slush-lake ice, and stability of the snow cover on the slope. Its variability (orographically conditioned) may diversify in time and space the reactions of the other cryosphere components to the changes in the air temperature. 3. Due to the different orographic conditions, interannual variability of the seasonal and perennial, surface and subsurface deposits of ice in
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