sector are displayed; the other sectors did not display any fundamentally different
result. From this analysis, it appears that all climatic models differ significantly from
the SAFRAN reanalysis, which is not surprising given the well-known difficulty of
climatic modelling and downscaling [104]. In particular, the BCC-CSM, CanESM2,
CSIRO-Mk3 and Aladin-Climat models do not bear the appropriate scales of
low-frequency variability. For instance, the low-frequency variability found in
BCC-CSM does not have the same scales as in the SAFRAN reanalysis (i.e. the
5–7- and 16–19-year scales), and the magnitudes associated with the annual cycle
are overestimated. The CSIRO-Mk3 and CanESM2 products fail to show any
significant variability above the 10-year scale, which is inconsistent with observations [50, 59] (Fig. 7). In contrast, MIROC5 precipitation outputs generally entail the
closest-matching scales of variability, even if a lack of energy can be noted for the
5–7-year scale, which is the case for all models. Therefore, MIROC5 was selected as
input for hydrological forecasts of the 2100s scenario to illustrate the potential
changes in the hydrosystem functioning.
5.4 Water Resources Trajectory from the 1900s to the 2100s
How the Seine basin evolved from the 1900s to the 2100s was evaluated. For each
case evaluated, the variations in fluxes are expressed according to a reference
simulation under the assumption that the bias on climate forcings is stationary
between the simulated and the reference periods. The reference simulations are
either (1) the average state of the system previously simulated (2000s, Fig. 5) for
the 1900s scenario
4 or (2) the average simulated state using MIROC5 climate data
over the same period, for the 2100s scenario.
5.4.1 Water Budget and Recharge Modes
Like many other basins across western and northern Europe, the Seine discharge
displays strong seasonality that is mainly driven by the quasi-sinusoidal fluctuation
of the actual evapotranspiration throughout the hydrological year, whereas the
precipitation input is much more stable over time in the reference simulation
(Fig. 8). This growing seasonal gap in rainfall has an impact on the infiltration/
runoff partition rate, which can especially be observed on the 2100s scenario.
Indeed, despite a similar effective rainfall rate when compared to the 2000s simulation (Table 2), a relative variation in runoff of +14.0% is simulated, along with a
4 A proper comparison between the 1900s and the 2000s should consider the average hydrosystem
state forced by Bonnet’s meteorological forcings [21] rather than the SAFRAN reanalysis. However, a visual comparison between the two simulations shows that they are very close (data not
shown). For readability the SAFRAN reanalysis is used in the remainder of the paper.
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N. Flipo et al.
result. From this analysis, it appears that all climatic models differ significantly from
the SAFRAN reanalysis, which is not surprising given the well-known difficulty of
climatic modelling and downscaling [104]. In particular, the BCC-CSM, CanESM2,
CSIRO-Mk3 and Aladin-Climat models do not bear the appropriate scales of
low-frequency variability. For instance, the low-frequency variability found in
BCC-CSM does not have the same scales as in the SAFRAN reanalysis (i.e. the
5–7- and 16–19-year scales), and the magnitudes associated with the annual cycle
are overestimated. The CSIRO-Mk3 and CanESM2 products fail to show any
significant variability above the 10-year scale, which is inconsistent with observations [50, 59] (Fig. 7). In contrast, MIROC5 precipitation outputs generally entail the
closest-matching scales of variability, even if a lack of energy can be noted for the
5–7-year scale, which is the case for all models. Therefore, MIROC5 was selected as
input for hydrological forecasts of the 2100s scenario to illustrate the potential
changes in the hydrosystem functioning.
5.4 Water Resources Trajectory from the 1900s to the 2100s
How the Seine basin evolved from the 1900s to the 2100s was evaluated. For each
case evaluated, the variations in fluxes are expressed according to a reference
simulation under the assumption that the bias on climate forcings is stationary
between the simulated and the reference periods. The reference simulations are
either (1) the average state of the system previously simulated (2000s, Fig. 5) for
the 1900s scenario
4 or (2) the average simulated state using MIROC5 climate data
over the same period, for the 2100s scenario.
5.4.1 Water Budget and Recharge Modes
Like many other basins across western and northern Europe, the Seine discharge
displays strong seasonality that is mainly driven by the quasi-sinusoidal fluctuation
of the actual evapotranspiration throughout the hydrological year, whereas the
precipitation input is much more stable over time in the reference simulation
(Fig. 8). This growing seasonal gap in rainfall has an impact on the infiltration/
runoff partition rate, which can especially be observed on the 2100s scenario.
Indeed, despite a similar effective rainfall rate when compared to the 2000s simulation (Table 2), a relative variation in runoff of +14.0% is simulated, along with a
4 A proper comparison between the 1900s and the 2000s should consider the average hydrosystem
state forced by Bonnet’s meteorological forcings [21] rather than the SAFRAN reanalysis. However, a visual comparison between the two simulations shows that they are very close (data not
shown). For readability the SAFRAN reanalysis is used in the remainder of the paper.
76
N. Flipo et al.