Climate change impacts and vulnerability in Europe 2016

Changes in the climate system
3.2.3 Heat extremes
Key messages
• The number of warm days (those exceeding the 90th percentile threshold of a baseline period) have almost doubled since
1960 across the European land area.
• Europe has experienced several extreme heat waves since 2000 (2003, 2006, 2007, 2010, 2014 and 2015). Under a high
emissions scenario (RCP8.5), very extreme heat waves as strong as these or even stronger are projected to occur as often
as every two years in the second half of the 21st century. The impacts will be particularly strong in southern Europe.
Relevance
The increase in the global surface temperature is
expected to affect the frequency and intensity of
extreme events, such as heat extremes (Fischer and
Schär, 2010; Stott et al., 2011; Russo et al., 2014). The
severity of a heat wave depends on a number of factors,
including its duration, its relative intensity (how much
hotter than normal) and its absolute intensity.
Heat extremes are often associated with droughts
because dry soil reduces evaporative cooling and thus
increases the magnitude of a heat wave (Mueller and
Seneviratne, 2012). On the other hand, heat extremes
can increase the frequency and intensity of heavy
precipitation events (including hailstorms), because
warmer air can hold a greater quantity of water
(Kendon et al., 2014).
Heat extremes also have strong direct impacts on
human health and well-being, as well as on society
(e.g. through decreased labour productivity), ecosystems
(e.g. through forest fires) and agriculture. In particular,
heat waves exacerbated by the urban heat island effect
and air pollution can have devastating impacts on
human health in urban areas.
Past trends
Observational data show a continued increase in
heat extremes over land in the period 1997–2012)
(Seneviratne et al., 2014). At the global scale, warm
days and nights, as well as heat waves, have become
more frequent in recent decades. The increase in
maximum daily temperatures has generally been
faster than the increase in annual average temperature
(IPCC, 2013). In Europe, since the 1950s, large areas have
experienced intense and long heat waves, with notable
impacts on human health and socio-economic systems
(García‐Herrera et al., 2010; Russo et al., 2015). As a
result, 500-year-old temperature records were broken
over 65 % of Europe in the period 2003–2010 alone
(Barriopedro et al., 2011).
Indices for extreme temperatures, including the annual
maximum value of daily maximum temperature (Tx x ),
have shown significant upwards trends across Europe
since the 1950s (Donat, Alexander, Yang, Durre, Vose,
and Caesar, 2013). The number of unusually warm
days (Tx90p) has increased by up to 10 days per decade
since 1960 in most of southern Europe and Scandinavia
(Map 3.5). Based on the daily Heat Wave Magnitude
Index (HWMId), Europe has experienced 11 intense and
long heat waves between 1950 and 2015, most of which
occurred after 2000 (in 2003, 2006, 2007, 2010, 2014
and 2015) (Russo et al., 2015). The most severe heat
waves have been characterised by the persistence of
extremely high night-time temperatures (Russo et al.,
2015). A substantial fraction of the probability of recent
extreme events can be attributed to human-induced
climate change, and it is likely that, for temperature
extremes occurring over previous decades, a fraction
of their probability was attributable to anthropogenic
influences (King et al., 2016).
Projections
Periods with extreme high temperatures are projected
to become more frequent and to last longer across
Europe during this century (Fischer and Schär, 2010;
Russo et al., 2014; Schoetter et al., 2014). Projections
based on a multi-model ensemble agree on increases in
heat wave frequency and magnitude for most European
regions during the 21st century under all RCP scenarios.
Extreme summer heat waves, such as the ones
experienced in different parts of Europe in 2003 and
2010, will become much more common in the future.
Under the RCP8.5 scenario, very extreme heat waves ( 43 )
( 43 ) To assess changes in heat waves, the HWMI has been used. The HWMI is defined based on the magnitude and length of heat waves in a year,
where heat waves are periods of at least three consecutive days with a maximum temperature above the threshold for the reference period
1981–2010. For details, including the definition of very extreme heat waves, see Russo et al., 2014.
Climate change, impacts and vulnerability in Europe 2016 | An indicator-based report
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