data sets [101] for the 1900s scenario. However, no raw data are available before
1950. Thus, these spatial distributions were considered to be steady over the
1900–1950 period, given its negligible variation during the first half of the twentieth
century [102]. Forested areas were also considered steady in the 2100s scenario
when compared to the present day.
Then, in the 1900s scenario only, land use was refined over the Paris area [1]
using data made available by the Urbanism and Land Use Institute for the Île-deFrance area (IAU
3 ). This additional step tends to integrate, as precisely as possible,
the significant extension of the urban area over time and its consequences on local
water budget calculations. In both cases, forested and urban area adjustments were
made at the expense or benefit of the proportion of agricultural lands over the entire
domain. These modifications were made assuming no significant changes in wetlands areas.
5.2 Estimating Anthropogenic Water Uptake
Projections from the Explore 2070 project [100] allowed integrating variation coefficients on present pumping rates in groundwater into the prospective 2100s simulation. These coefficients have been differentiated according to pumping types and
geographical location (data not shown). These projections, which were elaborated in
conjunction with demographic growth hypotheses and population migration processes, are based on extension of INSEE forecasts, i.e. the overall population rate of
the basin to over 21 million inhabitants in 2070 (Table 1). Regarding drinking water
withdrawals, forecasts expect a 40% increase in the number of households over the
2006–2070 period along with a decrease in water consumption, which has been
differentiated according to the habitat type (À0.3% per year for buildings, À0.6%
per year for private housing). A slight improvement in supply system efficiency is
also integrated (+0.2% per year). Three main variables are involved in hypotheses on
industrial-related withdrawals: production rate, past observed trends in water savings
and types of cooling circuits. These forecasts are based on a general 4.0% decrease in
water withdrawals per year, partly compensated with an increase in industrial
production. They also emphasise the pursuit of cooling circuit closures along
continuous improvements in water use efficiency of production processes. Finally,
irrigation requirements are calculated according to crop types, integrating plant
water demand, rainfall over agricultural lands as well as water efficiency of irrigation
techniques (gravity-fed or drip irrigation). It remains important to bear in mind that
these projections do not account for any impact of climate change, especially in the
case of seasonal pumpings.
To summarise, the implementation of the Explore 2070 projections resulted in a
decrease of the total volume withdrawn of 16.7% with ranges of variation of À2.5,
3 https://en.iau-idf.fr/.
Pluri-annual Water Budget on the Seine Basin: Past, Current and Future Trends
73
1950. Thus, these spatial distributions were considered to be steady over the
1900–1950 period, given its negligible variation during the first half of the twentieth
century [102]. Forested areas were also considered steady in the 2100s scenario
when compared to the present day.
Then, in the 1900s scenario only, land use was refined over the Paris area [1]
using data made available by the Urbanism and Land Use Institute for the Île-deFrance area (IAU
3 ). This additional step tends to integrate, as precisely as possible,
the significant extension of the urban area over time and its consequences on local
water budget calculations. In both cases, forested and urban area adjustments were
made at the expense or benefit of the proportion of agricultural lands over the entire
domain. These modifications were made assuming no significant changes in wetlands areas.
5.2 Estimating Anthropogenic Water Uptake
Projections from the Explore 2070 project [100] allowed integrating variation coefficients on present pumping rates in groundwater into the prospective 2100s simulation. These coefficients have been differentiated according to pumping types and
geographical location (data not shown). These projections, which were elaborated in
conjunction with demographic growth hypotheses and population migration processes, are based on extension of INSEE forecasts, i.e. the overall population rate of
the basin to over 21 million inhabitants in 2070 (Table 1). Regarding drinking water
withdrawals, forecasts expect a 40% increase in the number of households over the
2006–2070 period along with a decrease in water consumption, which has been
differentiated according to the habitat type (À0.3% per year for buildings, À0.6%
per year for private housing). A slight improvement in supply system efficiency is
also integrated (+0.2% per year). Three main variables are involved in hypotheses on
industrial-related withdrawals: production rate, past observed trends in water savings
and types of cooling circuits. These forecasts are based on a general 4.0% decrease in
water withdrawals per year, partly compensated with an increase in industrial
production. They also emphasise the pursuit of cooling circuit closures along
continuous improvements in water use efficiency of production processes. Finally,
irrigation requirements are calculated according to crop types, integrating plant
water demand, rainfall over agricultural lands as well as water efficiency of irrigation
techniques (gravity-fed or drip irrigation). It remains important to bear in mind that
these projections do not account for any impact of climate change, especially in the
case of seasonal pumpings.
To summarise, the implementation of the Explore 2070 projections resulted in a
decrease of the total volume withdrawn of 16.7% with ranges of variation of À2.5,
3 https://en.iau-idf.fr/.
Pluri-annual Water Budget on the Seine Basin: Past, Current and Future Trends
73