Snow cover (CLIM 008) - Assessment published Mar 2014
Climate change (Primary topic)
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)
- CLIM 008
Key policy question: What is the trend in snow cover extent and snow mass in Europe?
- Snow cover extent in the Northern Hemisphere has declined significantly over the past 90 years, with most of the reductions occurring since 1980. Snow cover extent has decreased by 7% on average in March and April and by 53% in June over the 1967–2012 period.
- Snow mass in the Northern hemisphere has decreased by 7 % in March from 1982 to 2009; snow mass in Europe has decreased even more, but with large inter-annual variation.
- Model simulations project widespread reductions in the extent and duration of snow cover in Europe over the 21st century.
- Changes in snow cover affect the Earth’s surface reflectivity, water resources, the flora and fauna and their ecology, agriculture, forestry, tourism, snow sports, transport and power generation.
Satellite observations on the monthly snow cover extent in the Northern Hemisphere are available since 1967. 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. A detailed analysis of Northern hemisphere snow cover based on multiple sources shows significant decreases in snow cover extent during the spring melting season (March to June); changes in other seasons are not significant. The decrease over the period 1967 to 2012 was 7% on average in March and April and 53% in June (Figure 1) [i].
Decreases in snow cover extent are caused by an earlier onset and a shorter duration of the snow-melting season. Since 1972, the duration of the snow season averaged over the Northern Hemisphere declined by 5 days per decade, but with substantial regional variation. The duration of the snow season has decreased by up to 25 days in western, northern and eastern Europe due to earlier spring melt whereas it has increased by up to 15 days in southeastern Europe due to an earlier onset [ii].
Trends in snow depth 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 [iii]. In other mountain regions such as the Carpathians, Tatra, Pyrenees, and Caucasus, there have been either decreasing or variable trends [iv]. 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 this region, but snow conditions correlate strongly with large-scale circulation patterns as indicated by the NAO [v].
The snow mass (i.e. the amount of water that the snow contains) is another important variable describing seasonal snow. For the whole Northern Hemisphere, a 7 % decrease in March snow mass has been observed between 1982 and 2009 [vi]. An extension of this data focusing on EEA member countries demonstrates a stronger average decline of more than 20 % for the period 1980-2012, although the year-to-year variation is large (Figure 2).
Northern Hemisphere snow cover will continue to shrink as temperatures rise [vii]. The multi-model mean from the CMIP5 modelling exercise projects changes in March/April snow cover extent in the Northern Hemisphere during the 21st century from 7 % for a low emission scenario (RCP 2.6) to 25 % for a high emission scenario (RCP 8.5) (Figure 3). Projected reductions in snow mass range from about 10 % for RCP2.6 to about 30 % for RCP8.5; projected reductions in the duration of the snow season range from about 10 days for RCP2.6 to about 40 days for RCP8.5 [viii]. Significant reductions in snow mass in Europe are likely to occur in Switzerland [ix], the alpine range of Italy [x], the Pyrenees [xi], the Turkish mountains [xii] and Balkan mountains [xiii]. In these areas the change can have dramatic down-stream effects as melt water contributes up to 60–70 % of annual river flows. Despite the projected decrease in long-term mean snow mass in the Northern Hemisphere, model simulations indicate occasional winters of heavy snowfall, but these become increasingly uncommon towards the end of the 21st century.
[i] 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): 219–29, doi:10.5194/tc-5-219-2011; D. G. Vaughan et al., “Observations: Cryosphere,” inClimate Change 2013: The Physical Science Basis., ed. T. F. Stocker et al. (Cambridge, United Kingdom and New York, NY, USA: Cambridge University Press, 2013), Chapter 4, http://www.climatechange2013.org/images/report/WG1AR5_Chapter04_FINAL.pdf.
[ii] Gwangyong Choi, David A. Robinson, and Sinkyu Kang, “Changing Northern Hemisphere Snow Seasons,”Journal of Climate 23, no. 19 (October 2010): 5305–10, doi:10.1175/2010JCLI3644.1; M. Takala et al., “Detection of Snowmelt Using Spaceborne Microwave Radiometer Data in Eurasia From 1979 to 2007,”IEEE Transactions on Geoscience and Remote Sensing 47, no. 9 (2009): 2996–3007, doi:10.1109/TGRS.2009.2018442.
[iii] Iris T Stewart, “Changes in Snowpack and Snowmelt Runoff for Key Mountain Regions,”Hydrological Processes 23, no. 1 (January 1, 2009): 78–94, doi:10.1002/hyp.7128; Daniele Bocchiola and Guglielmina Diolaiuti, “Evidence of Climate Change within the Adamello Glacier of Italy,”Theoretical and Applied Climatology 100, no. 3–4 (August 14, 2009): 351–69, doi:10.1007/s00704-009-0186-x; 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; Christoph Marty and Roland Meister, “Long-Term Snow and Weather Observations at Weissfluhjoch and Its Relation to Other High-Altitude Observatories in the Alps,”Theoretical and Applied Climatology 110, no. 4 (December 1, 2012): 573–83, doi:10.1007/s00704-012-0584-3.
[iv] 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, no. 1–2 (2003): 33–52, doi:10.1023/A:1024460010140; 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.
[v] Brown and Robinson, “Northern Hemisphere Spring Snow Cover Variability and Change over 1922–2010 Including an Assessment of Uncertainty”; Ewa Bednorz, “Synoptic Conditions of the Occurrence of Snow Cover in Central European Lowlands,”International Journal of Climatology 31, no. 8 (June 30, 2011): 1108–18, doi:10.1002/joc.2130.
[vi] 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, no. 12 (December 2011): 3517–29, doi:10.1016/j.rse.2011.08.014.
[vii] Vaughan et al., “Observations: Cryosphere.”
[viii] 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, no. 4 (August 8, 2012): 3317–48, doi:10.5194/tcd-6-3317-2012.
[ix] BAFU,Auswirkungen Der Klimaänderung Auf Wasserressourcen Und Gewässer. Synthesebericht Zum Projekt «Klimaänderung Und Hydrologie in Der Schweiz» (CCHydro)., vol. 2012, Umwelt-Wissen 1217 (Bern: Bundesamt für Umwelt, Bern., 2012).
[x] A. Soncini and D. Bocchiola, “Assessment of Future Snowfall Regimes within the Italian Alps Using General Circulation Models,”Cold Regions Science and Technology 68, no. 3 (September 2011): 113–23, doi:10.1016/j.coldregions.2011.06.011.
[xi] 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, no. 3–4 (2009): 384–96, doi:10.1016/j.jhydrol.2009.06.049.
[xii] M. Özdoğan, “Climate Change Impacts on Snow Water Availability in the Euphrates-Tigris Basin,”Hydrology and Earth System Sciences 15, no. 9 (2011): 2789–2803, doi:10.5194/hess-15-2789-2011.
[xiii] 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.
Monthly Northern Hemisphere Snow Cover Extent
provided by Rutgers University Global Snow Lab
Final Report. GlobSnow Deliverable 3.5. GlobSnow.
provided by Finnish Meteorological Institute (FMI)
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