annual scale in terms of water availability (Table 3), low-flow rate analysis clearly
confirms the trend leading to lower discharges in summer (Table 3), with a progressive reduction in VCN30 spread with time, underlying a potential increase in the
frequency of the occurrence of severe low-water discharges (Fig. 8d). This trend is
not new and rather in line with the transformation of the hydrological regime of the
Seine basin since the 1900s (Fig. 8c). These observations are in agreement with
former simulations of the impact of climate change [6, 9]. Climate change will have a
large impact on water resources management in the future, with higher discharges in
winter and lower ones from April to October. The increase of the low-flow period in
the future should also lead to very critical low-flow periods in October, which
emphasises the need for water management adaptation strategies.
6 Conclusion
Like every other river basin in the world, the Seine River basin faces global changes,
either anthropogenic or climatic. The long-term environmental research programme,
PIREN-Seine, allowed us to perform research on the Seine hydrosystem
sustainability.
First, the analysis of long-term discharge data over 130 years at Paris displays the
past trends, meaning long-term control of the discharge by climate and also the
development of large water reservoirs that store 840 Mm
3 of water during winter and
its release for sustaining low-flow discharge over 60 m
3 s
À1 at Paris. The latter has
significantly transformed the hydrological regime of the Seine River by reducing the
variability of monthly discharges since its implementation in the last quarter of the
twentieth century.
In the last few decades, a distributed physically based coupled model of surface
and subsurface flows, CaWaQS, was also developed and progressively refined in
terms of aquifer units and the river network description, as well as processes such as
river–aquifer exchanges. It establishes the first published water budget of the whole
Seine basin hydrosystem over a 17-year NAO oscillation period, including average
exchange fluxes between aquifer layers, as well as between the river network and its
underlying free aquifer units, mostly composed of an alluvial plain for Strahler
orders higher than 3.
Coupled with significant progress in hydrometeorology and climate research, this
model was used to assess the Seine basin hydrological trajectory from the 1900s to the
2100s. It reveals relative stability in the average annual discharges over the entire
basin over time coupled with substantial changes in the hydrological regime since the
1900s, starting one century ago with the decrease of low-flow discharges during low
flow in September and the decrease of its annual variability. This first change led to a
50% decrease of the average August discharge at the basin’s outlet, one-third of it due
to the gradual implementation of groundwater uptakes. The analysis of the climate
82
N. Flipo et al.
confirms the trend leading to lower discharges in summer (Table 3), with a progressive reduction in VCN30 spread with time, underlying a potential increase in the
frequency of the occurrence of severe low-water discharges (Fig. 8d). This trend is
not new and rather in line with the transformation of the hydrological regime of the
Seine basin since the 1900s (Fig. 8c). These observations are in agreement with
former simulations of the impact of climate change [6, 9]. Climate change will have a
large impact on water resources management in the future, with higher discharges in
winter and lower ones from April to October. The increase of the low-flow period in
the future should also lead to very critical low-flow periods in October, which
emphasises the need for water management adaptation strategies.
6 Conclusion
Like every other river basin in the world, the Seine River basin faces global changes,
either anthropogenic or climatic. The long-term environmental research programme,
PIREN-Seine, allowed us to perform research on the Seine hydrosystem
sustainability.
First, the analysis of long-term discharge data over 130 years at Paris displays the
past trends, meaning long-term control of the discharge by climate and also the
development of large water reservoirs that store 840 Mm
3 of water during winter and
its release for sustaining low-flow discharge over 60 m
3 s
À1 at Paris. The latter has
significantly transformed the hydrological regime of the Seine River by reducing the
variability of monthly discharges since its implementation in the last quarter of the
twentieth century.
In the last few decades, a distributed physically based coupled model of surface
and subsurface flows, CaWaQS, was also developed and progressively refined in
terms of aquifer units and the river network description, as well as processes such as
river–aquifer exchanges. It establishes the first published water budget of the whole
Seine basin hydrosystem over a 17-year NAO oscillation period, including average
exchange fluxes between aquifer layers, as well as between the river network and its
underlying free aquifer units, mostly composed of an alluvial plain for Strahler
orders higher than 3.
Coupled with significant progress in hydrometeorology and climate research, this
model was used to assess the Seine basin hydrological trajectory from the 1900s to the
2100s. It reveals relative stability in the average annual discharges over the entire
basin over time coupled with substantial changes in the hydrological regime since the
1900s, starting one century ago with the decrease of low-flow discharges during low
flow in September and the decrease of its annual variability. This first change led to a
50% decrease of the average August discharge at the basin’s outlet, one-third of it due
to the gradual implementation of groundwater uptakes. The analysis of the climate
82
N. Flipo et al.