Climate change and snow cover in the European Alps

Abstract

Climatic changes are already having a significant impact on snow cover in the European Alps. Several studies from Switzerland, France, Austria, Italy and Germany have noted a general decrease in snow depth and snow cover duration since the end of the 1980s throughout the European Alps. Investigations of snow cover and climate change have revealed that the reduction in snow reliability observed in low and medium altitude ski resorts is mainly caused by warmer winter temperatures. Precipitation becomes the determining factor for a snowy winter only above 2000 m asl. Projected changes in temperature and precipitation are expected to cause further significant decline in the snowreliability of Alpine ski areas. The impacts of these changes, however, are not uniform. They depend on altitude, region and local factors. For example, the impact of climate change is stronger at low altitudes, in inner-alpine dry valleys and on southern slopes, which leads to winners and losers among the different ski areas. The winter tourism industry has already begun to respond to the implications of these observed changes. A range of technological and behavioural measures have been put into practice to offset the adverse impacts. However, adaptation measures, such as the widespread use of snow-making, put new pressures on the ecology of the mountain environment.

Full text

30 The Impacts of Skiing on Mountain Environments, 2013, 30-44
Christian Rixen and Antonio Rolando (Eds)
All rights reserved-© 2013 Bentham Science Publishers
CHAPTER 2
Climate Change and Snow Cover in the European Alps
Christoph Marty*
WSL Institute for Snow and Avalanche Research SLF, Unit Snow and Permafrost,
Flüelastrasse 11, 7260 Davos-Dorf, Switzerland
Abstract: Climatic changes are already having a significant impact on snow cover in
the European Alps. Several studies from Switzerland, France, Austria, Italy and
Germany have noted a general decrease in snow depth and snow cover duration since
the end of the 1980s throughout the European Alps. Investigations of snow cover and
climate change have revealed that the reduction in snow reliability observed in low and
medium altitude ski resorts is mainly caused by warmer winter temperatures.
Precipitation becomes the determining factor for a snowy winter only above 2000 m asl.
Projected changes in temperature and precipitation are expected to cause further
significant decline in the snowreliability of Alpine ski areas. The impacts of these
changes, however, are not uniform. They depend on altitude, region and local factors.
For example, the impact of climate change is stronger at low altitudes, in inner-alpine
dry valleys and on southern slopes, which leads to winners and losers among the
different ski areas. The winter tourism industry has already begun to respond to the
implications of these observed changes. A range of technological and behavioural
measures have been put into practice to offset the adverse impacts. However, adaptation
measures, such as the widespread use of snow-making, put new pressures on the
ecology of the mountain environment.
Keywords: Adaptation measures, precipitation change, snow depth, snow
reliability, temperature change, winter tourism.
INTRODUCTION
Snow influences human life and society in many ways. The amount and duration
of snow in a ski-resort has high socio-economic significance for tourism. Many
mountain towns and villages depend heavily on snow, because their economy is
dominated by winter tourism (by up to 90 %) [1]. The vast majority of customers
of such ski areas live in the pre-alpine regions of Switzerland, Austria, Germany,
*Address correspondence to Christoph Marty: WSL Institute for Snow and Avalanche Research SLF,
Unit Snow and Permafrost, Flüelastr. 11, 7260 Davos Dorf, Switzerland: Tel: ++41 81 4170168; Fax: ++41
81 4170110; E-mail: marty@slf.ch
Send Orders of Reprints at bspsaif@emirates.net.ae

Climate Change and Snow Cover
The Impacts of Skiing on Mountain Environments 31
Italy and France. A longer sequence of almost snowless winters in these heavily
populated regions, such as observed between the late 1980s and mid 1990s,
caused problems for some ski areas and initiated a discussion about how
exceptional were such winters. To test for possible connections with climate
change, a number of studies have tried to investigate past variability, and to
predict future trends, for Alpine snow cover.
The financial viability of winter tourism depends to a great extent on favourable snow
conditions and reliable snow in the ski areas. A certain amount of snow is required to
groom the slopes, protect the ground, guarantee safe operation of the slopes, and to
provide the skiers with an enjoyable experience. The minimum snow depth from an
operational point of view, which may differ from the skiers’ perspective, depends on
the nature of the slopes. In general, a snow depth of 30 cm is considered sufficient, 50
cm good, and 70 cm excellent [2]. However, rocky slopes at higher elevations may
require much greater snow depths to be skiable (up to 1 m).
To investigate the impact of climate change on winter tourism in the Alps, it is
therefore important to understand the notion of natural snow reliability. Various
criteria have been proposed in the literature to assess the natural snow reliability of
ski areas. The so-called 100-day rule, first suggested by Witmer [2] is the most
widely accepted definition. According to this rule, there is natural snow reliability if
it is possible to successfully operate a ski area with sufficient snow cover for skiing
for at least 100 days during 7 out of 10 seasons [3]. However, there is no generally
applicable minimum snow depth to operate slopes, as this depends on the
characteristics of the resort and slopes, e.g., rockiness or north–south orientation.
In the Swiss Alps, Laternser and Schneebeli [4] found that the criteria for the 100-
day rule with a 30 cm threshold for snow depth, are currently fulfilled by areas at
altitudes above about 1300 m asl. This suggests that one of the conditions required
to run a successful ski business under current climate conditions in Switzerland is a
minimum elevation of about 1300 m asl, which is assumed to be the line of natural
snow-reliability (Fig. (1)). But this line varies across the Alpine is due to the
considerable variation in Alpine climate. Colder regions will have natural snow-
reliability at lower altitudes than warmer regions. Wielke et al. [5]

32 The Impacts of Skiing on Mountain Environments Christoph Marty
Figure 1: Probability of good, medium and bad winters for a ski area in the eastern Swiss Alps
with a mean altitude at 1200 m asl for past (1958-2007) and future (2030) conditions. The 100-day
rule can only be fulfilled with the 20 cm threshold for past winters (violet) and 10 cm threshold for
future winters (brown). The red numbers show the percentage change between past and future
winters (1 December - 15 April).
compared snow cover duration in the Alps and found the patterns in Switzerland
and Austria were similar, but comparable features were located about 150 m
higher in Switzerland than in eastern Austria. This indicates a transition from an
Atlantic-maritime to a more continental climate, with colder winters in the more
eastern parts of the Alps. The baseline of natural snow-reliability as established in
Switzerland is therefore probably 150 m lower (i.e. at 1050 m asl) in eastern
100
80
60
40
20
0>0 >10 >20 >30 >40 >50
Snow depth > x [cm]
100
80
60
40
20
0
Relative Frequency [%]
100
80
60
40
20
0
-19 -16
-14
-13
-10 -9
10 7
5-1 -4 -4
9 9 913 13
13
2005
2030
>= 100 days (good winter)
40 =< days < 100 (medium winter)
< 40 days (bad winter)

Climate Change and Snow Cover
The Impacts of Skiing on Mountain Environments 33
Austria. On the other hand, Marty [6] showed that the ski resorts above 1300 m
asl on the southern side of the Swiss Alps experience about 20 % fewer snow
days, i.e. days with at least 50 cm of snow, than the ski resorts on the northern
side of the Alps. This indicates that the line of natural snow-reliability for ski
areas influenced by a warmer Mediterranean climate is lower than that for the
northern parts of the Alps.
Some Alpine countries have a relatively dense network of measurement stations,
where daily snow depth and snowfall have been measured with the help of a
permanently mounted snow stake and a new snow board for 50 years or more.
The availability of this comprehensive dataset, as well as the socio-economic
importance of snow in Alpine countries, make the Alps a preferred region to
investigate changes in snow cover. The measurement locations are not always in
ski resorts, but are often close by or at similar altitudes and regions. Remote-
sensing data for Alpine snow cover have not yet been used for climatological
purposes due to the lack of longer time series and the limited data quality arising
from the steep topography of the Alps.
This chapter provides an assessment of the impacts of climate change on snow cover
(snow reliability) on ski areas in the European Alps. I present: 1) an overview of
observed snow cover changes in the different Alpine countries, 2) the results of
climate change scenarios for future snow cover, and finally 3) some adaptation
strategies adopted by ski area managers. The implications of this assessment,
however, extend beyond the European Alps. Insights into adaptation strategies, for
example, are also likely to be relevant for other mountain regions facing similar
climatic changes, such as North America, Australia and New Zealand.
OBSERVED CHANGES
The seasonal snow cover in the Alps is primarily influenced by high year-to-year
variability due to anomalies in large-scale weather patterns [7]. Several studies have
nevertheless noted a general decrease in snow depth and snow cover duration since
the end of the 1980s at low-lying stations throughout the European Alps.
In the Swiss Alps, a significant decrease in snow depth for elevations below 1300 m
asl was observed in the late 20th century with measurements from more than 100

34 The Impacts of Skiing on Mountain Environments Christoph Marty
stations [8], whereas no significant differences could be detected for high-altitude
stations above 2000 m asl [30]. The long-term snow trends in the Swiss Alps appear
to be similar for all three variables: snow depth, the duration of continuous snow
cover and the number of snow fall days [4]. Earlier investigations concluded that the
length of the snow season and the amount of snow have substantially decreased
since the mid 1980s, but during several periods in the records, e.g., in the 1930s, the
snow depth was as low as during the late 1980s [9]. However, a newer study using
more data from the last 130 years indicated that the series of snow-poor winters over
the 20-year period from 1988 to 2007 was unique [6]. In particular, it showed that
the decline was caused by an abrupt change, rather than by a continuous decrease
(Fig. (2)). The number of snow days, i.e. days with snow depth of at least 30 cm, at
ski resorts between 800 and 1200 m asl, for example, dropped by about 35 % after
the end of the 1980s compared to the long-term mean before the change. The
determining signal for this change was mainly temperature and not precipitation [6,
8], and this has had considerable impact on the mean evolution of snow cover during
the last twenty years (Fig. (3)).
Figure 2: Number of snow days, i.e. days with at least 30 cm snow on the ground (with exception
of Innsbruck (20 cm) and Col de Porte (50 cm)), at ski resorts in 6 Alpine countries. All stations
show a striking shift towards significantly less snow in the last 20 years. The values are based on
10-year low-pass filtered values of annual snow days between December and March.
In the Austrian Alps, various snow parameters at 98 long-term stations were
investigated and a more diverse picture was found [10]. The two 20-year periods
120
100
80
60
40
20
0
Snow Days
201020001990198019701960195019401930
Col de Porte, FR 1325m
Engelberg, CH 1060m
Hohenpeissenberg, DE 977m
Auronzo, IT 864m
Kranjska Gora, SLO 812m
Innsbruck, AT 577m

Climate Change and Snow Cover
The Impacts of Skiing on Mountain Environments 35
between 1980 and 2000 and between 1896 and 1916 were compared and tested
for changes. Statistical tests detected decreasing trends at the majority of the
stations, but the decline was only significant at the southern Austrian stations.
There, a clearly decreasing trend was found for the duration of winter snow cover
and the days with snow depths of more than 1 cm. A separate analysis of 14
stations with 100 years of data revealed similar results with snow day trends in
southern Austria mostly significantly decreasing and no significant trends in the
remaining parts of the country.
Figure 3: The less snowy winters during the last 20 years result in a clear reduction of the snow
depth during the winter season, as shown here for the ski resort of Engelberg in the Swiss Alps.
Note that the spring snow cover seems to be more affected than early-winter snow cover.
In the Italian Alps, a general decrease in snow depth and snow duration during the
last twenty years was found in the analyzed time series between 1920 and 2009
using data from 30 stations [11]. The authors relate this decrease to reduced snow
fall, which in turn may be caused by a higher ratio of liquid precipitation due to
warmer winter temperatures as recently demonstrated [31]. The spring reduction
in snow depth was not as unique as the reduction over the whole winter.
Surprisingly, these results were confirmed by 20 stations situated between 2000
and 3000 m asl in a small area in northern Italy [12]. In the German Alps, a 20-30
50
45
40
35
30
25
20
15
10
5
0
Snow Depth (cm)
Engelberg, 1060 m a.s.l.
20 Years
1989 - 2008
80 Years
1909 - 1988
Oct Nov Dec Jan Feb Mar Apr May
Averaged Daily Values
Running Mean

36 The Impacts of Skiing on Mountain Environments Christoph Marty
% reduction in snow cover duration was found for low-lying areas between 1952
and 1996 [13]. A smaller reduction of about 10 % was observed in higher areas.
In the French Alps, snow trends between 1958 and 2005 were investigated with
the help of an automatic system that combined three numerical models to simulate
meteorological parameters and snow stratigraphy [14]. As input data, the system
was fed with meteorological observations and 40 years re-analysis data (ERA-40)
from the European Centre for Medium-range Weather Forecasts (ECMWF). The
few available long-term snow observations were finally used for verification. The
results demonstrate a significant decrease in snow depth at low and mid altitudes,
but this signal is weaker in the south than in the north and less visible at high
elevations. Concerning snow duration, a shift in the mean values at the end of the
1980s confirmed the finding reported in Marty [6]. The results have also been
interpreted in terms their implications for a viable ski industry. French downhill
ski resorts are currently economically viable above elevations ranging from about
1200 m asl in the northern foothills to 2000 m in the south.
FUTURE CHANGES
Climate models today can successfully reproduce large-scale parameters such as
temperature. However, investigations on the evolution of the future snow pack
under changing climate conditions all battle with the fact that the current climate
models have difficulties in representing the fine-scaled spatial and temporal
variability of snow. Some studies therefore use physical models driven by
artificially generated data of future weather conditions to predict the snow depth
and duration at local levels. Other studies estimate future snow conditions based
on a sensitivity analysis of the current variability.
For example, Hantel and Hirtl-Wielke [15] assessed the snow-temperature
sensitivity in the European Alps based on data recorded during the past 40 years
at 268 stations and came to the conclusion that the number of snow days (days
with snow depths greater than 5cm) will decrease by 33% per 1°C increase in
temperature. This corresponds to a reduction of snow cover duration of about 1
month at the altitude of maximum sensitivity (about 700 m asl), but falls rapidly
above and below that level. The future snow reliability of 666 Alpine ski resorts
in 6 European countries was investigated by Abegg et al. [16]. They calculated

Climate Change and Snow Cover
The Impacts of Skiing on Mountain Environments 37
the impact of temperature increases of 1°C, 2°C and 4°C based on the assumption
that the altitudinal limit of natural snow-reliability will rise by 150 m per 1°C
warming. They concluded that the number of naturally snow-reliable areas would
drop by 25% with a temperature increase of 1°C, by 40% with 2°C, and by 70 %
with a 4°C warming (Fig. (4)).
Figure 4: Number of naturally snow-reliable ski areas in the European Alps under present and
future climate conditions. Regions with low-altitude ski areas, for example in southern Germany,
are most affected by future warming (Adapted from Abegg et al. [16]).
Future Austrian snow conditions were analyzed using a simple temperature- and
precipitation-dependent snow model by Breiling and Charamza [17]. They
concluded that the impact of 2°C warming would mean only a few locations at
higher altitudes would be suitable for winter tourism and skiing. None of these
studies [15-17] took into account the local influences of topography or orientation
at each location, and they assumed that the current sensitivity of the snow cover
will not change in the future.
The other approach of coupling existing snow-cover models with meteorological
input data from regional climate models (RCMs) for future climate scenarios was

38 The Impacts of Skiing on Mountain Environments Christoph Marty
first applied by Beniston et al. [18] in the Swiss Alps. Using a single-layer snow-
cover model and assuming a 4°C temperature increase by the end of this century,
they found a 50 % reduction in snow volume with a termination of the season
about 50 days earlier at 2000 m asl. For the French Alps, Martin and Etchevers
[19] used future temperature fields from a GCM as input for their multi-layer
snow-cover model. They found a 50 % reduction in snow depth below 1500 m asl
and 30 % smaller snow covered area in mid-winter with a 1.8 °C temperature
increase, when precipitation was kept constant. They concluded that changes of
this magnitude could have a major impact on the skiing industry in the French
Alps, especially at lower elevations. The length of the skiing season could
decrease substantially and ski areas may increasingly move into less temperature-
sensitive high-elevation areas.
The sensitivity of snow cover to future climate has recently been analyzed at 20
ski resorts in the Swiss Alps using a more sophisticated approach [20]. With a
well-elaborated perturbation method and RCM model data as input for their single
layer snow cover model, the researchers computed snow reliability at the end of
this century with a predicted 4° C increase in temperature. With this scenario,
snow will become scarce on the lower ski runs in all resorts and days when the
snow depth is more than the critical 30 cm snow depth will drastically decrease at
more than half of the stations. In addition, at the critical altitude, i.e. the altitude
above which snow is required for the ski lifts to run, more than half of the
stations, on average, will have snow depths below the critical 30-cm level.
Hydrological studies that investigate the impact of climate change on snow cover
as a water resource can often also be used for the analysis of snow reliability of
ski resorts, which are situated within water catchments. Potential future changes
in two such Alpine river basins (above 800 m asl) in the Swiss Alps have been
investigated with the help of the distributed catchment model WaSiM-ETH [21].
According to 23 regional climate models, 2.5°C warming and small changes in
precipitation can be expected by the end of the 21st century. The model predicted
a decrease of 70 % in the annual mean snow-water equivalent, two months less
continuous snow cover and a snowline rise of 450 m. Bavay et al. [22] and
Magnusson et al. [23] focused on three other alpine river basins (above 1600 m
asl) using the spatially distributed model system Alpine3D and the IPCC A2 and

Climate Change and Snow Cover
The Impacts of Skiing on Mountain Environments 39
B2 scenarios output from 6 RCMs. Their results indicated that the snow volume
and the maximum snow water equivalent at the end of the 21st century are likely
to be reduced by about 40%. The complete melt of the snow cover will occur
about 40 days earlier and the snow line will be shifted by about 900 m, which
would mean most of the glaciers in these basins would disappear and limit the
natural snow reliability to altitudes above 2000 m asl.
ADAPTATION STRATEGIES
Managers of ski areas and stakeholders in tourism are not just waiting to see what
the consequences of climate change are, but have already begun to prepare for less
snowy winters [3, 24-26]. They realize that the ski industry is highly dependent on
snow conditions and that snow-deficient winters pose a risk. Adaptation practices
found among ski area operators can be divided into two main categories:
technological and behavioral [16].
Technological adaptations appear so far to be the adaptation strategies most
favored by tourism stakeholders in the European Alps. The three main types are
listed here in order of priority. Their impacts on the mountain environment are
discussed in detail in the other chapters:
 Landscaping: This strategy involves the landscaping of large ski areas
(e.g., machine-grading or bulldozing of ski runs, creation of shaded
areas) and the contouring or smoothing of smaller areas (e.g., the
leveling of rough and bumpy surfaces, and the removal of obstacles
such as rocks and shrub vegetation). The aim is to reduce the snow
depth required for ski operation, which also means a reduction of the
necessary amount of artificial snow.
 Artificial snow-making: Snow-making is used to extend the operating
season and to increase the range of climate variability and climate
change with which a ski area can cope. While artificial snow-making
was initially viewed as a luxury and then a back up strategy, it now
appears to be viewed as a necessity. According to Pröbstl [27], the
rapid expansion of snow-making in the Alps was triggered by the need

40 The Impacts of Skiing on Mountain Environments Christoph Marty
to secure and guarantee the revenues of the ski area managers and by
the success of the ski resorts that could provide a "snow guarantee".
 Going higher and facing north: The aim of this strategy is to
concentrate ski operations in locations with a climatic advantage. The
different options for this strategy include: moving operations to the
upper part of an existing ski area or building new ski areas on north-
facing slopes, at higher elevations and possibly on glaciers.
Behavioral adaptations range from new business models and new financial tools
to a change in operational practices and a move towards the diversification of
activities:
 Mergers and corporations: A very common form of cooperation is the
merger of different companies in one valley or even from neighboring
valleys with the aim of reducing marketing and operational costs. Another
form of cooperation is the regional association, which offers one ski pass
for several ski areas. A less well-known form of cooperation is the
collaboration between a small low-altitude, but close-to-the-city, ski area
and a large mountain ski area to "nurse" future customers and to have a
marketing platform close to heavily populated regions.
 Financial support: A growing number of ski area managers consider
snow-making to be a public service and therefore claim that all those who
benefit should contribute to the costs. The options go from sharing the
cost of snow-making with the accommodation sector to governmental
subsidies for the ski area. Local authorities can, for example, make one-
off or annual contributions, issue loans or take a share in the business.
This is highly beneficial for a ski resort as the local authorities generally
receive better financial ratings than ski area managers.
 Diversification: Many resorts have made substantial investments to
cater for the growing market of non-skiers. The most popular
activities are winter hiking, tobogganing and snowshoeing. The
problem, of course, with these non-ski related activities is that they

Climate Change and Snow Cover
The Impacts of Skiing on Mountain Environments 41
also require snow, although less than for downhill skiing. Moreover,
these new activities, which often take place in previously undisturbed
surroundings, may cause new problems for some animals already
struggling to cope with the harsh winter environment.
However, these strategies cannot all be causally linked only to climate change, as
trends in tourism, prestige, and competitive advantage are also important factors.
Figure 5: Snow as a resource: Artificial snow from the previous winter is preserved during
summer under a thick layer of woodchips at 1600 m asl in Davos, Switzerland. In the early winter
of the same year, this pile of snow will help to produce a cross-country ski track. Such
management of snow supplies and snow reserves is called snow farming. Snow farming is
nowadays practiced by many ski resorts in order to keep the slopes well-stocked with snow to
attract visitors (Photo: SLF).
DISCUSSION AND IMPLICATIONS
The seasonal snow cover in the Alps is primarily influenced by a high year-to-
year variability due to large-scale weather patterns. Despite this variability, a
general decrease in snow depth and snow cover duration has been apparent since
the end of the 1980s at low-lying stations throughout the European Alps. The

42 The Impacts of Skiing on Mountain Environments Christoph Marty
decline could be linked to the anomalously warm winter temperatures during the
last twenty years [6, 8], which seem to be unique over at least the last 500 years
[28]. During the past 100 years in Switzerland, for example, the observed
warming has been roughly twice as high as the global average [29].
The development of winter tourism and skiing infrastructure in the European Alps
during the past 30 years has tended to follow the decadal temperature variations.
The period 1965-1985, when an expansion of ski areas occurred, was a relatively
cold one. The period 1985-1995, was considerably warmer, and most winter
resorts had snow problems during this time, many of them serious, and artificial
snow making became popular. A rise of just 0.8 °C in temperature necessitated
considerable adaptation, which is still required today.
Research on future snow cover has taken two different approaches, one based on
physical models and the other based on current snow-temperature sensitivity.
Assuming 2°C warming, both came to similar results: Snow depth will drastically
decrease by about 40-60% below 1800 m; the snow cover will last 4 to 6 weeks
less and the snow line will rise by about 300-500 m. According to the RCM
projections, the warming in the Alps will be accompanied by a small increase in
winter precipitation. Some authors therefore concluded that, at higher altitudes,
where the temperatures are still cold enough for substantial snowfall, the snow
depth may even increase with climate warming. However, the outcomes of two
recent studies imply that the projected increase in winter precipitation over the
Alps will not compensate for the projected increase in temperature even at the
higher resorts [20, 22].
These projected changes in temperature and precipitation will most certainly be a
challenge for the winter tourism sector. Since the Alpine snow cover is very
sensitive to temperature, the depth, length and duration of the snow cover is
greatly influenced by climate change. As warming progresses in future, regions
where snowfall is the current norm will increasingly experience rain, and the
snow on the ground will melt faster. To mitigate the effects of this process,
innovative technical solutions and behavioral adaptations are needed to conserve
energy and to ensure the mountain environment is harmed as little as possible.
Sophisticated storage methods, (see Fig. (5)), or improved artificial snow

Climate Change and Snow Cover
The Impacts of Skiing on Mountain Environments 43
production may help to safeguard winter tourism in regions where few other
economic resources are available. Future perspectives leave no doubt, however,
that the projected climate changes will have considerable impact on the economic,
social, hydrological and biological systems in the Alpine region.
CONFLICT OF INTEREST
The author confirms that this article content has no conflict of interest.
ACKNOWLEDGEMENTS
The author gratefully acknowledges data from Meteoswiss, DWD, Meteo France,
Arpa Veneto, Regione Autonoma Valle d'Aosta, Environmental Agency of the
Republic of Slovenia, University of Innsbruck and the European Climate
Assessment & Dataset project.
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