Climate change impacts and vulnerability in Europe 2016

Changes in the climate system
3.3.5 Snow cover
Key messages
• Snow cover extent in the northern hemisphere has declined significantly over the past 90 years, with most of the
reductions occurring since 1980. Over the period 1967–2015, snow cover extent in the northern hemisphere has
decreased by 7 % on average in March and April and by 47 % in June; the observed reductions in Europe are even larger,
at 13 % for March and April and 76 % for June.
• Snow mass in the northern hemisphere is estimated to have decreased by 7 % in March from 1982 to 2009; snow mass in
Europe has decreased more rapidly than the average for the northern hemisphere, but with large interannual variation.
• Model simulations project widespread reductions in the extent and duration of snow cover in the northern hemisphere
and in Europe over the 21st century.
• Changes in snow cover affect the Earth's surface reflectivity, water resources, flora and fauna and their ecology,
agriculture, forestry, tourism, snow sports, transport and power generation.
Relevance
Snow influences the climate and climate-related
systems because of its high reflectivity, insulating
properties, effects on water resources and ecosystems,
and cooling of the atmosphere. A decrease in snow
cover accelerates climate change (Flanner et al., 2011).
In Europe, about half of the population lives in areas
that have snow cover in January in an average winter.
Changes in snow cover affect human well-being
through effects on water availability, hydropower,
navigation, infrastructure, the livelihoods of indigenous
Arctic people, environmental hazards, winter recreation
and outdoor light conditions. Variation in snow cover
affects winter road and rail maintenance, as well as the
exploitation of natural resources (ACIA, 2005; UNEP,
2007).
Past trends
Satellite observations of monthly snow cover extent
in the northern hemisphere are available from 1967
onwards (Estilow et al., 2015). A detailed analysis
based on multiple sources shows there have been
significant decreases in northern hemisphere snow
cover extent during the spring melt season since
about 1980 (March to June; Figure 3.14, left) (Brown
and Robinson, 2011; Vaughan et al., 2013); in other
seasons, the snow cover extent has remained stable
or even slightly increased. A separate analysis for
Europe (EEA-39 region) shows even larger reductions
of 13 % for March and April, and 76 % for June
between 1980 and 2015 (Figure 3.14, right).
Decreases in snow cover extent are caused by an
earlier onset of melting and a shorter duration of the
snow season. Since 1972, the duration of the snow
season averaged over the northern hemisphere
declined by five 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 south-eastern Europe
due to an earlier onset of the snow season (Choi et al.,
2010; Mioduszewski et al., 2015).
The snow mass (i.e. the amount of water that the snow
contains) is an important variable, as it affects the role
of snow in the hydrological cycle. For the whole of the
northern hemisphere, a 7 % decrease in March snow
mass was observed between 1982 and 2009 (Takala
et al., 2011). An extension of these data focusing on
EEA member countries demonstrate a stronger average
decline of 30 % for the period 1980–2015, although
the year-to-year variation is large (Figure 3.15). Winter
increases in precipitation have also led to an increase in
snow mass at higher altitudes in Norway.
102 Climate change, impacts and vulnerability in Europe 2016 | An indicator-based report