the trajectory of the system is evaluated based on a downscaled climate reanalysis of
the twentieth century and a reconstruction of the land use in the early 1900s, as well
as the choice of a climate projection which favours the model that best reproduces
the low frequency of precipitation. The trajectory is synthesised as average regimes,
revealing a relative stability of the hydrosystem up to the present, and drastic
changes in the discharge regime in the future, especially concerning the decreased
amount of low flow and its increased duration. These expected changes will require
the definition of an adaptation strategy even though they are rather limited in the
Seine basin when compared to other French regions.
Keywords CaWaQS, Climate change, Groundwater, Hydrological distributed
modelling, Land use, Past and future scenarios, Seine basin, Surface water, Water
budget
1 Introduction
As mentioned by Flipo et al. [1] and Billen et al. [2], the Seine hydrosystem is unique
due to the tremendous pressure exerted by the largest metropolis in Europe, Greater
Paris, on water resources and the fact that it contains the largest groundwater
reservoir in Europe, the Paris basin [3]. Today, the total water withdrawal reaches
the enormous amount of 3 Gm
3 a
À1 . Coupled with climate change, this pressure may
hinder the sustainability of this unique hydrosystem.
Since the international effort to quantify the effect of climate change on global
water circulation crystallised around the successive climate model intercomparison
projects [4, 5], the expected effects of climate change on French water resources
have been estimated [6, 7]. To evaluate water resources at the scale of a regional
hydrosystem, it is now acknowledged that regional-scale models calibrated and
validated against observed discharge should be used [8]. Following this effort, a
first regional assessment at the Seine basin scale [9] led to the same conclusion as the
nation-wide assessment [6, 7], meaning that heavier rainfall events are expected
during winter and longer, more intense low-flow events may occur from May to late
October.
Assessments of climate change impacts on regional hydrosystems are not sufficiently mature to be synergistically used with climate change adaptation decisionmaking [10, 11] designed to optimise what are called climate services [12]. These
processes involve the full understanding of the regional system trajectory over
decades or centuries. These approaches usually only consider the trajectory from
now to tomorrow. At the Seine basin scale, the PIREN-Seine research programme
promotes the study of trajectories from the past to today until tomorrow. This attempt
to map the hydrosystem trajectory is the goal of this chapter. We believe that
switching the cognitive reference from today to yesterday provides a broader view
of the combined functioning of the anthro-eco-hydrosystem and it makes complete
sense to evaluate climate services and possible adaptation strategies in a “safe
operating space” [13].
60
N. Flipo et al.
the twentieth century and a reconstruction of the land use in the early 1900s, as well
as the choice of a climate projection which favours the model that best reproduces
the low frequency of precipitation. The trajectory is synthesised as average regimes,
revealing a relative stability of the hydrosystem up to the present, and drastic
changes in the discharge regime in the future, especially concerning the decreased
amount of low flow and its increased duration. These expected changes will require
the definition of an adaptation strategy even though they are rather limited in the
Seine basin when compared to other French regions.
Keywords CaWaQS, Climate change, Groundwater, Hydrological distributed
modelling, Land use, Past and future scenarios, Seine basin, Surface water, Water
budget
1 Introduction
As mentioned by Flipo et al. [1] and Billen et al. [2], the Seine hydrosystem is unique
due to the tremendous pressure exerted by the largest metropolis in Europe, Greater
Paris, on water resources and the fact that it contains the largest groundwater
reservoir in Europe, the Paris basin [3]. Today, the total water withdrawal reaches
the enormous amount of 3 Gm
3 a
À1 . Coupled with climate change, this pressure may
hinder the sustainability of this unique hydrosystem.
Since the international effort to quantify the effect of climate change on global
water circulation crystallised around the successive climate model intercomparison
projects [4, 5], the expected effects of climate change on French water resources
have been estimated [6, 7]. To evaluate water resources at the scale of a regional
hydrosystem, it is now acknowledged that regional-scale models calibrated and
validated against observed discharge should be used [8]. Following this effort, a
first regional assessment at the Seine basin scale [9] led to the same conclusion as the
nation-wide assessment [6, 7], meaning that heavier rainfall events are expected
during winter and longer, more intense low-flow events may occur from May to late
October.
Assessments of climate change impacts on regional hydrosystems are not sufficiently mature to be synergistically used with climate change adaptation decisionmaking [10, 11] designed to optimise what are called climate services [12]. These
processes involve the full understanding of the regional system trajectory over
decades or centuries. These approaches usually only consider the trajectory from
now to tomorrow. At the Seine basin scale, the PIREN-Seine research programme
promotes the study of trajectories from the past to today until tomorrow. This attempt
to map the hydrosystem trajectory is the goal of this chapter. We believe that
switching the cognitive reference from today to yesterday provides a broader view
of the combined functioning of the anthro-eco-hydrosystem and it makes complete
sense to evaluate climate services and possible adaptation strategies in a “safe
operating space” [13].
60
N. Flipo et al.