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Indicator Assessment
Trend in autumn, winter and spring snow cover extent over the Northern Hemisphere
Past trends
Satellite observations on the monthly snow cover extent in the Northern Hemisphere are available since November 1966 [i]. Figure 1 shows that snow covered on average 45 % of the land area of the Northern Hemisphere in winter (December to February), varying from less than 41 % in 1980–1981 to over 48 % in 1977–1978 [ii]. Satellite data shows that there are no trends from 1967 to 2010 in snow cover in fall (September-November) and winter (December-February), but snow cover in spring has decreased significantly. According to a detailed statistical analysis of the snow cover in the Northern hemisphere the rate of decrease in March and April in the period 1970–2010 was around 0.8 million km2 per decade, corresponding to a 7 % decrease in March and an 11 % decrease in April from the pre-1970 values [iii]. Trends in snow cover vary in different parts of Europe. In some mountain regions, such as the Alps and the Norwegian mountains, snow depth has decreased at low elevations where the temperature increased over the freezing point whereas it has increased at high elevations where both precipitation and temperature have increased but the temperature has remained below the freezing point for extended periods [iv]. In other mountain regions such as the Carpathians, Tatra, Pyrenees, and Caucasus, there have been either decreasing or variable trends [v] [vi]. In the lowlands of western Europe, snow is not a permanent winter phenomenon — it may come and go several times during the cold months. Decreasing snow cover trends have been observed in, for example, Britain[vii], Germany[viii], Poland [ix] and Nordic countries[x]. In general, snow conditions in these areas correlate strongly with large-scale circulation patterns as indicated by the NAO [xi] [xii]. The snow mass (i.e. the amount of water that the snow contains) is another important variable describing seasonal snow. In the Northern Hemisphere, a 7 % decrease has been observed between 1982 and 2009 for March[xiii]. An extension of this data focusing on EEA member countries, excluding mountain areas, also demonstrates this decline (Figure 2).
Projections
The seasonal snow cover is likely to continue shrinking [xiv]. Figure 3 shows projections of changes in annual snow fall days based on a multi-model ensemble. The multi-model mean shows decreases in days with snow fall exceeding 1 cm across Europe. Days with snow fall above 10 cm show increases in large parts of northern Europe and decreases in most other regions. There is, however, considerable uncertainty in these projections due to large differences between the upper and lower limits of the model projections. Because snow cover is sensitive to snowfall as well as temperature, increased snowfall will not necessarily translate into more snow on the ground [xv]. A study has projected a reduced number of snow cover days in northern Europe (defined as 55–70 °N, 4.5–30 °E) of up to 40–70 days in 2071–2100 compared to the baseline period 1961–1990. The study used a RCM driven by an ensemble of 7 GCMS for 4 SRES emission scenarios[xvi]. The projections depend on the emission scenario and the underlying GCM simulation. Model projections of 21st century change in snow water equivalent (SWE) in the Northern Hemisphere under the SRES A1B emissions scenario suggest that SWE increases in the coldest parts of the Northern Hemisphere continents, but decreases elsewhere [xvii]. The multi-model mean from the CMIP5 modelling exercise projects changes in March/April snow cover in the Northern Hemisphere during the 21st century of about 7 % and 27 % in a low emission scenario (RCP 2.6) and a high emission scenario (RCP 8.5), respectively [xviii]. Despite the projected decrease in long-term mean SWE in the Northern Hemisphere, model simulations indicate occasional winters of heavy snowfall, but these become increasingly uncommon towards the end of the 21st century. Significant reductions in snow mass in Europe are likely to occur in Switzerland[xix], the alpine range of Italy[xx], the Pyrenees[xxi], the Turkish mountains[xxii] and Balkan mountains [xxiii]. In these areas the change can have dramatic effects as melt water contributes up to 60–70 % of annual river flows.
[i] RUGSL, „Fall, Winter, and Spring Northern Hemisphere Snow Cover Extent from the Rutgers University Global Snow Lab“, Climate Science: Roger Pielke Sr., 2011, http://pielkeclimatesci.wordpress.com/2011/05/30/fall-winter-and-spring-northern-hemisphere-snow-cover-extent-from-the-rutgers-university-global-snow-lab/.
[ii] RUGSL, „Fall, Winter, and Spring Northern Hemisphere Snow Cover Extent from the Rutgers University Global Snow Lab“.
[iii] R. D. Brown and D.A. Robinson, „Northern Hemisphere spring snow cover variability and change over 1922–2010 including an assessment of uncertainty“, The Cryosphere 5 (2011): 219–229, doi:10.5194/tc-5-219-2011.
[iv] Daniele Bocchiola and Guglielmina Diolaiuti, „Evidence of climate change within the Adamello Glacier of Italy“, Theoretical and Applied Climatology 100, Nr. 3–4 (August 14, 2009): 351–369, doi:10.1007/s00704-009-0186-x; Iris T Stewart, „Changes in Snowpack and Snowmelt Runoff for Key Mountain Regions“, Hydrological Processes 23, Nr. 1 (Januar 1, 2009): 78–94, doi:10.1002/hyp.7128; A. V. Dyrral, Analysis of past snow conditions in Norway met.no report (Oslo: Norwegian Meteorological Institute, 2010), http://met.no/Forskning/Publikasjoner/filestore/ClimateReport_10_2010.pdf.
[v] Henry F. Diaz et al., „Variability of Freezing Levels, Melting Season Indicators, and Snow Cover for Selected High-Elevation and Continental Regions in the Last 50 Years“, Climatic Change 59, Nr. 1–2 (2003): 33–52, doi:10.1023/A:1024460010140.
[vi] M Lapin, P Faško, and J Pecho, „Snow Cover Variability and Trends in the Tatra Mountains in 1921–2006“, ed. V Ducrocq, Proceedings of the 29th International Conference on Alpine Meteorology, Chambery, France (Météo France, 2007), http://www.cnrm.meteo.fr/icam2007/ICAM2007/extended/manuscript_174.pdf.
[vii] Matthew Perry, A spatial analysis of trends in the UK climate since 1914 using gridded data sets, Bd. 2006, Climate Memorandum 21 (Devon: Met Office, 2006).
[viii] Rixa Schwarz, Sven Harmeling, and Christoph Bals, Auswirkungen des Klimawandels auf Deutschland (Berlin: Germanwatch, 2007), http://www.germanwatch.org/klima/klideu07.pdf.
[ix] Ewa Bednorz, „Synoptic Conditions of the Occurrence of Snow Cover in Central European Lowlands“, International Journal of Climatology 31, Nr. 8 (Juni 30, 2011): 1108–1118, doi:10.1002/joc.2130.
[x] Donna Wilson, Hege Hisdal, and Deborah Lawrence, „Has streamflow changed in the Nordic countries? – Recent trends and comparisons to hydrological projections“, Journal of Hydrology 394, Nr. 3–4 (November 26, 2010): 334–346, doi:10.1016/j.jhydrol.2010.09.010.
[xi] Bednorz, „Synoptic Conditions of the Occurrence of Snow Cover in Central European Lowlands“.
[xii] Brown and Robinson, „Northern Hemisphere spring snow cover variability and change over 1922–2010 including an assessment of uncertainty“.
[xiii] Matias Takala et al., „Estimating northern hemisphere snow water equivalent for climate research through assimilation of space-borne radiometer data and ground-based measurements“, Remote Sensing of Environment 115, Nr. 12 (Dezember 2011): 3517–3529, doi:10.1016/j.rse.2011.08.014.
[xiv] Stewart, „Changes in Snowpack and Snowmelt Runoff for Key Mountain Regions“.
[xv] Jouni Räisänen and Joonas Eklund, „21st Century changes in snow climate in Northern Europe: a high-resolution view from ENSEMBLES regional climate models“, Climate Dynamics (April 23, 2011), doi:10.1007/s00382-011-1076-3.
[xvi] Erik Kjellström et al., „21st Century Changes in the European Climate: Uncertainties Derived from an Ensemble of Regional Climate Model Simulations“, Tellus A 63, Nr. 1 (2011): 24–40, doi:10.1111/j.1600-0870.2010.00475.x.
[xvii] Jouni Räisänen, „Warmer climate: less or more snow?“, Climate Dynamics 30, Nr. 2–3 (Juli 12, 2007): 307–319, doi:10.1007/s00382-007-0289-y.
[xviii] C. Brutel-Vuilmet, M. Ménégoz, and G. Krinner, „An analysis of present and future seasonal Northern Hemisphere land snow cover simulated by CMIP5 coupled climate models“, The Cryosphere Discussions 6, Nr. 4 (August 8, 2012): 3317–3348, doi:10.5194/tcd-6-3317-2012.
[xix] BAFU, Auswirkungen der Klimaänderung auf Wasserressourcen und Gewässer. Synthesebericht zum Projekt «Klimaänderung und Hydrologie in der Schweiz» (CCHydro)., Bd. 2012, Umwelt-Wissen 1217 (Bern: Bundesamt für Umwelt, Bern., 2012).
[xx] A. Soncini and D. Bocchiola, „Assessment of future snowfall regimes within the Italian Alps using general circulation models“, Cold Regions Science and Technology 68, Nr. 3 (September 2011): 113–123, doi:10.1016/j.coldregions.2011.06.011.
[xxi] J.I. López-Moreno, S. Goyette, and M. Beniston, „Impact of climate change on snowpack in the Pyrenees: Horizontal spatial variability and vertical gradients“, Journal of Hydrology 374, Nr. 3–4 (elokuu 2009): 384–396, doi:10.1016/j.jhydrol.2009.06.049.
[xxii] M. Özdoğan, „Climate change impacts on snow water availability in the Euphrates-Tigris basin“, Hydrology and Earth System Sciences 15, Nr. 9 (2011): 2789–2803, doi:10.5194/hess-15-2789-2011.
[xxiii] FAO, Forests and climate change in Eastern Europe and Central Asia. Forests and Climate Change Working Paper 8 (Rome: Food and Agriculture Organization of the United Nations, 2010), http://www.fao.org/docrep/014/k9589e/k9589e.pdf.
In April 2013 the European Commission presented the EU Adaptation Strategy Package (http://ec.europa.eu/clima/policies/adaptation/what/documentation_en.htm). This package consists of the EU Strategy on adaptation to climate change /* COM/2013/0216 final */ and a number of supporting documents. One of the objectives of the EU Adaptation Strategy is Better informed decision-making, which should occur through Bridging the knowledge gap and Further developing Climate-ADAPT as the ‘one-stop shop’ for adaptation information in Europe. Further objectives include Promoting action by Member States and Climate-proofing EU action: promoting adaptation in key vulnerable sectors. Many EU Member States have already taken action, such as by adopting national adaptation strategies, and several have also prepared action plans on climate change adaptation.
The European Commission and the European Environment Agency have developed the European Climate Adaptation Platform (Climate-ADAPT, http://climate-adapt.eea.europa.eu/) to share knowledge on observed and projected climate change and its impacts on environmental and social systems and on human health; on relevant research; on EU, national and subnational adaptation strategies and plans; and on adaptation case studies.
No targets have been specified.
Satellite observations on the monthly snow cover extent in the Northern Hemisphere are available since November 1966 from the Rutgers University Global Snow Lab and from the Globsnow project. Trend lines have been added.
Multi-model mean of changes in annual snowfall days from 1971–2000 to 2041–2070 exceeding 1 cm and 10 cm are based on 6 RCM simulations and the emission scenario A1B.
Not applicable
No methodology references available.
Not applicable
Data on the cryosphere vary significantly with regard to availability and quality. Snow and ice cover have been monitored globally since satellite measurements started in the 1970s. Improvements in technology allow for more detailed observations and higher resolution. High quality long-term data is also available on glaciers throughout Europe.
Continuous efforts are being made to improve on knowledge of the cryosphere. Intensive development work is under way to develop projections, which are essential for scenarios of climate change impacts and adaptation. Due to their economic importance special effort is also devoted to improving real-time monitoring of, for example, snow cover.
Further information on uncertainties is provided in Section 1.7 of the EEA report on Climate change, impacts, and vulnerability in Europe 2012 (http://www.eea.europa.eu/publications/climate-impacts-and-vulnerability-2012/
No uncertainty has been specified
For references, please go to https://www.eea.europa.eu/data-and-maps/indicators/snow-cover-1/assessment or scan the QR code.
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