Climate change impacts and vulnerability in Europe 2016

Changes in the climate system
3.2.4 Mean precipitation
Key messages
• Annual precipitation since 1960 shows an increasing trend of up to 70 mm per decade in north-eastern and north‐western
Europe, and a decrease of up to 90 mm per decade in some parts of southern Europe. At mid-latitudes no significant
changes in annual precipitation have been observed. Mean summer precipitation has significantly decreased by up
to 20 mm per decade in most of southern Europe, while significant increases of up to 18 mm per decade have been
recorded in parts of northern Europe.
• Projected changes in precipitation vary substantially across regions and seasons. Annual precipitation is generally
projected to increase in northern Europe and to decrease in southern Europe. The projected decrease in southern Europe
is strongest in the summer.
Relevance
Precipitation plays a vital role in all environmental
systems and social sectors, including natural
ecosystems, agriculture, water supply, energy
production and tourism. Daily precipitation has been
recorded systematically in most of Europe since the
1950s. However, despite the length of precipitation
records, a climate change signal cannot be detected
with certainty in all European regions owing to the
high spatial and temporal variability of precipitation.
Difficulties in detecting trends can also arise from the
small sampling area of rain gauges, calibration errors in
instrumentation and erroneous measurements during
snow or gales (e.g. Hofstra et al., 2009).
Past trends
According to the E-OBS dataset (Haylock et al., 2008),
average annual precipitation across Europe shows no
significant changes since 1960. However, significant
changes have been observed at sub-continental
scales. Most precipitation studies show a tendency
towards wetter conditions in the northern hemisphere
throughout the 20th century, but the changes are
less spatially coherent than temperature change.
The majority of Scandinavia and the Baltic states
have observed an increase in annual precipitation of
greater than 17 mm per decade, which is as high as
70 mm per decade in western Norway (Map 3.7, left).
Winter precipitation (December to February) tends
to decrease in limited areas in southern Europe, and
significant increases (up to 70 mm per decade) have
been recorded in most of northern Europe (Maraun,
2013). In contrast, annual precipitation has decreased
by up to 90 mm per decade in the Iberian Peninsula,
in particular in central Portugal. Mean summer (June
to August) precipitation has significantly decreased
by up to 20 mm per decade in most of southern
Europe, while significant increases (up to 18 mm per
decade) have been recorded in parts of northern
Europe (Map 3.7, right) (van den Besselaar et al., 2013;
Casanueva et al., 2014).
Changes in large-scale circulation patterns (synoptic
atmospheric circulation) play a key role in the observed
changes in precipitation (Casanueva et al., 2014;
Fleig et al., 2015). It is not clear if the relatively minor
land‐use changes in Europe since the 1950s have
influenced observed precipitation trends (Taylor, 2015).
Projections
For a high emissions scenario (RCP8.5), the models
(ensemble mean) project a statistically significant
increase in annual precipitation in large parts of
central and northern Europe (of up to about 30 %) and
a decrease in southern Europe (of up to 40 %) from
1971–2000 to 2071–2100 (Map 3.8, left); in summer,
the precipitation decrease extends northwards
(Map 3.8, right) (Jacob et al., 2014). A zone with small
changes that are not significant (but are, however,
partially robust in the direction of the change), shows
where the precipitation pattern (as presented in
the ensemble mean) changes the direction of the
change. For a medium emissions scenario (RCP4.5),
the magnitude of change is smaller, but the pattern is
very similar to the pattern for the RCP8.5 scenario. The
range of projected changes in precipitation from the
multi‐model ensemble are generally the same between
RCP4.5 and RCP8.5, or larger in RCP8.5, especially at the
end of the century (Jacob et al., 2014).
80 Climate change, impacts and vulnerability in Europe 2016 | An indicator-based report