Download Climate Change and Natural Disasters in Switzerland

Climate Change and Natural Disasters
in Switzerland
Past and
Present
Climate has changed,
worldwide …
Since the late 19th century, the global
mean surface temperature has risen
by 0.8°C. There is a very high
probability that the warming of the
past 50 years is a consequence of
emissions of greenhouse gases and
aerosols caused by human activity.
These emissions are very likely also
the cause of the melting of polar sea
ice and of the widespread retreat of
glaciers1.
… and in Switzerland
• Since the beginning of systematic
recordings in 1864, the annual mean
temperature has increased in Northern
Switzerland by between 1.2°C and
1.5°C and in Southern Switzerland by
approx. 0.9°C 2;
• The past 15 years were among the
warmest in the past 500 years. The
four warmest years ever were all
recorded after 1990 3;
• During the 20th century, winter
precipitation in the region North of the
Alps and in Western Switzerland has
increased by 10 – 30% 4;
• Below the altitude of 1300 m, the
periods with snow covering have
become significantly shorter 5.
Debris flow in Brienz (BE) following the heavy precipitation event in August 2005.
© Schweizer Luftwaffe
At present it is not possible to prove
that
these
regionally
observed
changes are also man-made, since
the natural climate variability (mainly
the influence of the North Atlantic
Oscillation) plays an important role6. In
the light of what is known today,
however, such a connection is
plausible.
In the long series of measurements
available for Switzerland today, there is
no evidence for a systematic change in
the frequency of rare weather extremes.
Since a statistical detection can only be
expected in the case of massive
changes7, however, it cannot be
excluded that climate change has
already influenced the occurrence of rare
weather extremes.
Annual Temperature in Switzerland 1864-2006
Deviation from the mean 1961-1990
2.5
Deviation, degree C
Extreme weather events have
probably changed
Independently of climate change, there
have always been periods of frequent
and less frequent extreme weather
events. Especially where rare extremes
are concerned – for instance those that
cause substantial damage – these
random variations are very pronounced.
Eventual changes due to climate change
remain difficult to identify.
2.0
years below the norm 1961-1990
smoothed evolution in Switzerland
1.5
years above the norm 1961-1990
smoothed evolution over the Northern Hemisphere
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
1860
1880
1900
1920
1940
1960
1980
2000
year
Intense weather events have
changed in the past decades
In contrast to rare weather extremes,
systematic changes in intense weather
events can already be observed in the
long series of measurements available
for Switzerland. These are events that do
not, as a rule, cause significant damage.
• The number of exceptionally cold days
has decreased in the course of the 20th
century 8;
• The duration and intensity of heat
waves has increased 9;
• In autumn and winter (but not in
summer), intense precipitation has
become more frequent 10;
• In rivers north of the Alps, whose
catchment areas are still in a natural
state, peak volume has increased in
winter 11.
Whether this is a signal of the influence
of human activity on the climate remains
unclear.
However,
the
changes
correspond
qualitatively
to
the
expectations formulated by studies on
climate change.
In Northern Switzerland the frequency of intense precipitation events in winter
has clearly increased in the course of the 20th century 9.
2
What does the future have
in store?
The climate will continue changing …
n the coming decades, the increase of
greenhouse gases will continue to
influence the global climate. Worldwide,
this will have an impact on the
atmosphere, on the water cycle,
including snow and ice, on the oceans
and on the biosphere. In some areas, the
changes are well understood and a
quantitative estimate is possible. In other
areas there are major uncertainties. At
present, the following developments are
expected for Switzerland, for the mid
21st century 12,13:
…and with it the future weather
extremes
In the future, there will be shifts both in
the frequency and in the occurrence of
extreme weather events. The extent and
character of these modifications will vary
depending on the place and nature of the
events.
There are major uncertainties when one
tries to quantify these changes. Based
on
present
knowledge,
however,
Switzerland can expect 14,15,16:
• Fewer cold spells and frost days in
Switzerland.
• More frequent heat
droughts in the summer.
waves
and
These developments have an impact
on the natural disasters caused
by the weather
Whether Switzerland will be affected
more frequently by natural disasters in
the future will depend on the interplay
between the different climatic factors and
on local sensitivities. In order to make
quantitative estimates, detailed model
analyses will be generally necessary. On
the whole, it can be expected that the
following natural events will increasingly
threaten the Alpine region 17,18:
• An increase in precipitation and the
shift from snow to rain in the low lands
and the pre-Alps will probably lead to
more flooding along medium-sized to
large rivers.
• a warming by 1.0°C to 3.5°C;
• an increase of winter precipitation by
up to 20 %;
• a decrease of summer precipitation
by 5 to 30 %.
• In the winter half-year, more frequent
and more intense heavy precipitation.
• More intense precipitation is likely to
produce more mudslides and landslides.
Where other types of extreme weather
are concerned, such as storms or
hailstorms, the influence of climate
change is not yet sufficiently understood.
• The melting of permafrost will reduce
the stability of mountain slopes.
• Hotter summers will lead to more heatinduced stress for humans, animals and
plants and accordingly have an impact
on their health.
• Summer drought will influence forestry
and agriculture, navigation and water
resources.
In
part,
the
expected
changes
significantly exceed the natural climate
variations we have known so far. It can
therefore be assumed that society will
perceive these changes very clearly.
Change of
heavy precipitation
in winter, 2071-2100
with respect
to 1961-1990.
Scenario of a
selected regional
climate model.
3
Implications for society
The risk of natural disasters does not
only depend on the climate
The climate is not the only factor which
determines to what extent our society is
at the risk due to natural disasters.
Changes in society play an important
part as well. As a consequence of
increased human settlement pressure,
construction in areas that are more
exposed to potential danger has
increased.
In addition, improvements in the
standard of living imply that property of
ever increasing value is exposed to
danger. The potential for damage has
grown, and society has become more
sensitive
to
natural
disasters.
Depending
on
future
social
developments, the effects of climate
change could either intensify or be
mitigated17.
Climate change demands flexible
solutions
The time scale of the expected climate
change is comparable to the planning
horizon for new buildings, infrastructure,
and land use decisions. Where planning
is concerned, it will become ever more
important to take into account the
changing conditions of weather, climate
and natural disasters. This is especially
true for constructions that provide
protection from natural disasters.
Since there are still many uncertainties
concerning the future development of the
climate, it is at present difficult to define
measures, which are concrete and
universally valid. At the moment, the
focus should therefore be on flexible
solutions that are geared towards
present needs and that can be adapted
to more severe future requirements .
There are solutions already available
that provide better protection for little
extra expenditure, and are useful to
society regardless of climate change.
References
1 IPCC, 2007:Climate change 2007. Working Group
1, Fourth Assessment Report. WMO, UNEP, (in
press).
2
Begert, M., et al., 2005: Homogeneous
temperature and precipitation series of Switzerland
from 1864 to 2000. Int. J. Climatol., 25, 65-80.
3 Casty, C., et al., 2005: Temperature and
precipitation variability in the European Alps since
1500. Int. J. Climatol., 25, 1855-1880.
4 Schmidli, J., et al., 2002: Mesoscale precipitation in
the Alps during the 20th century. Int. J. Climatol., 22,
1049-1074.
5 Scherrer, S., et al., 2004: Trends in Swiss Alpine
snow days: The role of local- and large-scale climate
variability. Geophys. Res. Lett., 31, L13215,
doi:10.1029/2004GL020255.
6 Wanner, H., et al., 2001: North Atlantic Oscillation
– concepts and studies. Surv.Geophys. 22, 321-382.
7
Frei, C., et al., 2001: Detection probability of trends
in rare events: Theory and application to heavy
precipitation in the Alpine region. J. Climate, 14,
1564-1584.
8 Jungo, P., et al. , 2001: Changes in the anomalies
of extreme temperature anomalies in the 20th
century at Swiss climatological stations located at
different lati-tutdes and altitudes. Theor. Appl.
Climatol., 69, 1-12.
9 Della-Marta, P.M., et al., 2006: The length of
western European summer heatwaves has doubled
since 1880. J. Geophys. Res. (submitted).
10 Schmidli, J., et al. , 2005: Trends of heavy
precipitation and wet and dry spells in Switzerland
during the 20th century. Int.J. Climatol., 25, 753-771.
11 Birsan, M.-V., et al., 2005: Streamflow trends in
Switzerland. J. Hydrol., 314, 312-329.
12 Frei C., 2005: Die Klimazukunft der Schweiz –
Eine probabilistische Projektion. Bericht erhältlich
unter www.occc.ch und www.meteoschweiz.ch .
13 OcCC, 2006: Die Schweiz im Jahr 2050.
Beratendes Organ für Fragen der Klimaänderung.
(in Vorbereitung).
14 Schär, C., et al., 2004: The role of increasing
temperature variability in European summer
heatwaves. Nature, 427, 332-336.
15 Frei, C., et al., 2006: Future change of
precipitation
extremes
in
Europe:
An
intercomparison of scenarios from regional climate
models. J. Geophys. Res., 111, D06105,
doi:10.1029/2005JD005965.
16 Beniston, M., et al., 2006: Future extreme events
in European Climate: An exploration of regional
climate model projections. Clim. Change, (in press).
17
OcCC,
2003:
Extremereignisse
und
Klimaänderung. Beratendes Organ für Fragen der
Klimaänderung. 88pp. Erhältlich unter www.occc.ch.
18 Defila C., 2004: Der Sommer und Herbst aus
phänologischer Sicht. Schweiz. Z. Forstwesen, 155
(5), 142-145.
19 PLANAT 2004: Strategie Naturgefahren Schweiz.
Synthesebericht.
81
pp.
Erhältlich
unter
www.planat.ch
PD Dr. Christoph Frei
MeteoSwiss
Krähbühlstrasse. 58
8044 Zürich
T 044 256 91 11
www.meteoswiss.ch
Climate Information MeteoSchweiz
[email protected]
Mai 31st 2006
around 06.45 a
rockfall occurred
at the autobahn A2
in Gurtnellen.
Picture:
Walter Arnold,
Tiefbauamt des
Kanton Uri
Florian Widmer
National Platform for Natural Hazards
PLANAT
Federal Office for the Environment
FOEN
CH-3003 Bern
T 031 324 17 81
[email protected]
www.planat.ch
01/2007 © MeteoSchweiz, PLANAT
4