Climate change impacts and vulnerability in Europe 2016

Climate change impacts on society
5.3.5 Crop water demand
Key messages
• Climate change led to an increase in the crop water demand and thus the crop water deficit from 1995 to 2015 in large
parts of southern and eastern Europe; a decrease has been estimated for parts of north-western Europe.
• The projected increases in temperature will lead to increased evapotranspiration rates, thereby increasing crop water
demand across Europe. This increase may partly be alleviated through reduced transpiration at higher atmospheric CO 2
levels.
• The impact of increasing water requirements is expected to be most acute in southern and central Europe, where the
crop water deficit and irrigation requirements are projected to increase. This may lead to an expansion of irrigation
systems, even in regions currently without irrigation systems. However, this expansion may be constrained by projected
reductions in water availability and increased demand from other sectors and for other uses.
Relevance
Water is essential for plant growth and there is a
relationship between plant biomass production and
transpiration, with water-use efficiency (biomass
production per unit of water transpired) being affected
by crop species and management. The increasing
atmospheric CO 2 concentration will lead to higher
water‐use efficiency through reductions in plant
transpiration and increased photosynthesis (Box 5.1).
However, higher temperatures and lower relative
humidity will lead to higher evaporative demands, which
will reduce water-use efficiency. The resulting effect of
climate change on water-use efficiency will therefore be
the result of a combination of changes in climate and
atmospheric CO 2 concentration, as well as changes in
crop choice and management. The water demand by
crops must be met through rainfall during the growing
period, soil water storage or irrigation. In drought-prone
areas, increasing demands for water by industrial and
urban users intensify the competition for irrigation water
(Iglesias et al., 2007), and managing this requires an
integrated approach (Falloon and Betts, 2010).
Past trends
Irrigation in Europe is currently concentrated along the
Mediterranean, where in some countries more than
80 % of the total freshwater abstraction is used for
agricultural purposes (EEA, 2009). However, consistent
observations of water demand and consumption for
agriculture do not currently exist for Europe, partly
because of unrecorded water abstractions and national
differences in accounting and reporting. Modelling
approaches can be used to compute net irrigation
requirements. Two studies estimated the net irrigation
requirements in Europe for 1995–2002 and for the
year 2000 with a total of three different model systems
(Wriedt et al., 2009; aus der Beek et al., 2010). The results
show an irrigation requirement of up to 21–40 km 3 for
Spain, which had the highest net irrigation requirement
in the EU-27.
Crop water demand, defined as the water consumed
during the growing season, depends on the crop type
and the timing of the growing season. Water demand
can be modelled using meteorological data and
information on crop management, and the difference
between crop water demand and rainfall constitutes
the crop water deficit. Map 5.15 shows the change in
the crop water deficit for grain maize, which is a crop
that is often grown under irrigated conditions because
it is mostly grown during the summer season. The
hatched areas in Map 5.15 show the areas where crop
water demand exceeds average rainfall and thus may
have an irrigation demand. The trends for 1995–2015
show an increase in the crop water deficit for maize in
large parts of southern and eastern Europe; a decrease
has been estimated for parts of north-western Europe
Some of the effects of estimated changes in the crop
water deficit may also be related to the duration of
the crop growing period, which is shortened under
higher temperatures, thus leading to less water being
consumed.
Projections
A multi-model study using seven global hydrological
models driven by five global climate models under four
RCP scenarios estimated changes in irrigation water
demand (IWD) across regions during the 21st century.
Under the low and low-to-medium emissions scenarios
(RCP2.6 and RCP4.5, respectively), the simulated
changes in IWD across Europe were small. For RCP6.0,
the multi-model average suggests a substantial
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