(module) all fit around the 2000s values within a range of Æ10%. This first-order
relative stability of the average discharge has to be weighted, however, by the
temporal distribution of discharges, also called regime, and the analysis of extremes,
especially low-flow values. Two usual flow rates were therefore considered: (1) the
annual minimum flow rate calculated over a consecutive 30-day period (VCN30)
and (2) the mean monthly annual minimum discharge associated with a 5-year return
period (QMNA5).
The evolution of monthly discharges is in line with previous observations on
precipitation dynamics, meaning an evolution towards a winter situation
characterised by an increase of mean discharge rates as opposed to a decrease in
summer (Fig. 8). The hydrological regime of the Seine basin appears stable between
the 1900s and the 2000s, even though (1) natural discharges decrease significantly
during low flow everywhere in the basin (see QMNA5 in Table 3) and (2) the spread
of the low-flow discharge also significantly decreases, meaning more recurrent
low-flow periods (Fig. 8d). In September, one-third of the discharge decrease is
Fig. 10 Relative variations (RV) of average runoff (a, c) and infiltration rates (b, d) for the 1900s
(a, b) and 2100s scenarios (c, d). RVs are calculated with regard to their respective reference (2000s
for the 1900s scenario and MIROC5 in the current days for the 2100s scenario)
80
N. Flipo et al.
relative stability of the average discharge has to be weighted, however, by the
temporal distribution of discharges, also called regime, and the analysis of extremes,
especially low-flow values. Two usual flow rates were therefore considered: (1) the
annual minimum flow rate calculated over a consecutive 30-day period (VCN30)
and (2) the mean monthly annual minimum discharge associated with a 5-year return
period (QMNA5).
The evolution of monthly discharges is in line with previous observations on
precipitation dynamics, meaning an evolution towards a winter situation
characterised by an increase of mean discharge rates as opposed to a decrease in
summer (Fig. 8). The hydrological regime of the Seine basin appears stable between
the 1900s and the 2000s, even though (1) natural discharges decrease significantly
during low flow everywhere in the basin (see QMNA5 in Table 3) and (2) the spread
of the low-flow discharge also significantly decreases, meaning more recurrent
low-flow periods (Fig. 8d). In September, one-third of the discharge decrease is
Fig. 10 Relative variations (RV) of average runoff (a, c) and infiltration rates (b, d) for the 1900s
(a, b) and 2100s scenarios (c, d). RVs are calculated with regard to their respective reference (2000s
for the 1900s scenario and MIROC5 in the current days for the 2100s scenario)
80
N. Flipo et al.