timing of the floods varies gradually both from
the west to the east because of increasing continentality (distance from the Atlantic) and from
the south to the north because of the increasing
influence of snow-related processes. The effect
of snow storage and melt at high altitudes—for
example, in the Alps and the Carpathians (orange
to red arrows in Fig. 3)—is superimposed on this
spatial pattern. The spatial patterns of the average
timing of potential drivers, and their trends, are
shown in figs. S3 to S5.
Throughout northeastern Europe (Fig. 1, re-
gion 1), spring occurrence of snowmelt and floods
(yellow and green arrows in figs. S3 and S4A)
combined with a warmer climate (fig. S4A) has
led to earlier floods. In the region around the
North Sea (Fig. 1, region 2), extreme precipitation
and floods in the winter (blue arrows in Fig. 3
and fig. S3A) combined with a shift in the timing
of extreme winter precipitation (fig. S3B) has
led to later floods. In western Europe (Fig. 1,
region 3), winter occurrence of soil moisture
maxima and floods (blue arrows in Fig. 3 and
fig. S5A) combined with a shift in the timing of
soil moisture maxima (fig. S5B) has led to earlier
floods. Although region 3 shows a consistent be-
havior in flood timing changes, closely aligned
with those of soil moisture, the effects of chang-
ing storm tracks on precipitation are different
in southern England and northwestern Iberia
because of the opposite effects of the NAO.
If the trends in flood timing continue, consid-
erable economic and environmental consequences
may arise, because societies and ecosystems have
adapted to the average within-year timing of
floods. Later winter floods in catchments around
the North Sea, for example, would lead to softer
ground for spring farming operations, higher soil
compaction, enhanced erosion, and direct crop
damage, thereby reducing agricultural produc-
tivity (20). Spring floods occurring earlier in the
season in northeastern Europe may limit the re-
plenishment of reservoirs if managers expect
later floods that never arrive, with substantial
reductions in water supply, irrigation, and hy-
dropower generation (21). Our flood timing ob-
servations at the continental scale also enable the
identification of a clear climate change signal that
could not be obtained by earlier studies based on
flood magnitude data (4, 5, 22).
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Supported by ERC Advanced Grant “FloodChange,” project
no. 291152; the Austrian Science Funds (FWF) as part of the
Doctoral Programme on Water Resource Systems (W1219-N22);
the EU FP7 project SWITCH-ON (grant 603587); and Russian
Science Foundation project no. 14-17-00155. We acknowledge
the involvement in the data screening process of C. Álvaro Díaz,
I. Borzì, E. Diamantini, K. Jeneiová, M. Kupfersberger, and
S. Mallucci during their stays at the Vienna University of
Technology. We thank L. Gaál and D. Rosbjerg for contacting
Finish and Danish data holders, respectively; A. Christofides
for pointing us to the Greek data source; B. Renard (France),
T. Kiss (Hungary), W. Rigott (South Tyrol, Italy), G. Lindström
(Sweden), and P. Burlando (Switzerland) for assistance in
preparing and/or providing data or metadata from their
respective regions; and B. Lüthi and Y. Hundecha for
preparing supporting data that are not part of the paper, to
cross-check the results. The flood date data used in this paper
can be downloaded from www.hydro.tuwien.ac.at/fileadmin/
mediapool-hydro/Downloads/Data.zip. The precipitation and
temperature data can be downloaded from www.ecad.eu/
download/ensembles/ ensembles.php. The soil moisture data
can be downloaded from www.esrl.noaa.gov/psd.
Materials and Methods
Figs. S1 to S5
Tables S1 and S2
17 March 2017; accepted 30 June 2017
590 11 AUGUST 2017 • VOL 357 ISSUE 6351 sciencemag.org SCIENCE
Fig. 3. Observed average timing of river floods in Europe, 1960–2010. Each arrow represents
one hydrometric station (n = 4062). Color and arrow direction indicate the average timing of
floods, as indicated by the circular color scale (light blue, winter floods; green to yellow, spring
floods; orange to red, summer floods; purple to dark blue, autumn floods). Lengths of the
arrows indicate the concentration of floods within a year (0, evenly distributed; 1, all floods occur
on the same date).