Water at the Heart of Science
6
Assessment
is Crucial
While water is growing scarcer
and its quality is degrading, demands for it continue to grow.
It is therefore vital to assess the available resources as precisely as possible.
In this respect, scientific expertise is of the essence.
Observing
Understanding
Building a model
Water resources are first of
all assessed through numerous
direct measurements of river
flows, groundwater levels,
and water quality. These
may be supplemented by
other sources of information:
satellite images, user surveys…
To evaluate current water
resources more efficiently,
it is useful to know how they
evolved in the past.
By looking at archived
documents, sediment analyses,
fossilised pollen or treering records, scientists can
reconstruct former climates
and environments.
These data help scientists
to determine the causes of
changes in the resource, such
as climate variations or human
intervention. Once these
causes, which can vary greatly
from one region to another,
have been identified, they
can be analysed scientifically
to measure their respective
impact on water resources.
Researchers develop simplified
models to reproduce the
functioning of rivers, aquifers,
lakes, etc. These models
are used to test hypotheses
regarding their current state,
but also to simulate future
scenarios. This can help
decision-makers to define their
water management policies
more effectively.
1 A researcher takes a water sample
to analyse the Azufrera lagoon in the
northern part of Chile.
2 Researchers sometimes use a
geophysical method to determine the
water content of different subsurface soil
layers and detect groundwater.
4 By looking at fossilised pollen, it is
possible determine what types of plants
existed in the past, and to deduce the
climate that prevailed at the time. Pollen
from the Hibiscus tiliaceus, a plant that
typically grows in very humid climates.
7 Measuring the current in the Orinoco
during the flood season, in Venezuela.
These data help to determine the amount
of water that flows over a given period
of time.
5 Analysing water pollution in Ha Long
8 Satellite radar altimetry is used to
measure the level of major rivers.
Senegal River, Lake Guiers District,
Senegal.
Bay, Vietnam.
3 In 50 years, the rate of groundwater
extraction worldwide has at least tripled,
and the increase is continuing by 1 to 2%
each year. Wind pump in Brazil.
1
6 Researchers observe and analyse
sediments to reconstruct former
environments and climates. Niger.
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3
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Water at the Heart of Science
7
Models
Provide Insight and Foresight
Lake Chad
which today is a mosaic of islets and shallow water, has been shrinking rapidly since
the 1970s. Scientific research shows that this decline is caused by climate fluctuations
as well as human activity.
The surface area of Lake
To understand these
Chad today is 10 times
significant variations and
smaller than it was in 1963. foresee future changes,
For centuries, the level has
varied between very high in
humid periods, and very low,
a state referred to as
Small Chad.
researchers from a number
of scientific fields have been
joining forces. By looking at
weather data, river flows,
groundwater levels, sediment
records, etc., they have
developed a mathematical
model that simulates
the surface area of Lake
Chad according to climate
fluctuations and abstraction of
water for irrigation purposes.
The lake has been studied for a number of
years by research teams from IRD, universities
and institutions in France and other countries
bordering on the lake: the Universities of
Paris 11-Orsay, Aix-Marseille, Montpellier,
Avignon, Niamey, N’Djaména, Maïdougouri,
and Ngaoundéré, as well as CNRS, CBLT, the
ministries of Hydraulics in Chad and Niger,
PNUD, FAO, and UNESCO.
1963 - Normal Chad
Niger
Chad
1 On the Yaere floodplain
south of the lake, dykes
enable farmers and
fishermen to retain water
for longer periods. However,
considerable amounts
evaporate from the reservoir,
which greatly reduces the
intake of the lake.
2010 - Small Chad
Niger
Chad
Nigeria
Nigeria
Cameroon
50 km
These studies for instance
show that variations in the
surface temperature of the
Atlantic Ocean, which was
partly responsible for excessive
rainfall in the period 19501960, followed by deficient
rainfall since 1970, have
contributed to reducing water
levels in the lake. At the same
time, water extraction has
increased due to the growing
size of farming land and the
need to irrigate to compensate
for reduced rainfalls.
Surface area:
In 1963:
20,000 km2
Today:
2,000 to 15,000 km2
Former outline
Lowest level of the lake
Highest level of the lake
2 Lake Chad’s water intake
comes almost entirely from
rivers, in particular the Chari,
and only 10% from rain.
Cameroun
3 Away from the lake and
rivers, groundwater becomes
the only possible source to
supply in the needs of people
and their flocks, and to
develop irrigation.
1
Lake Chad
4 The shrinking water level
has compelled fishermen to
turn to farming on the fertile
land left exposed by the
withdrawing lake. The region
now produces maize, rice,
beans and peppers, which is
a high-yielding crop.
5 Like the Dead Sea, which
accumulates minerals from
the rivers that end in it, Lake
Chad should have been very
salty. However, scientific
studies show that these
mineral salts collect in the
water table underneath
the lake.
6 The level of Lake Chad has
always fluctuated. Historical
data and sediment analyses
show that the lake went
through at least four very low
levels between the years 900
and 1900. Collecting sediment
cores from the south basin
of Lake Chad.
7 Start of the annual flood of
the Komadougou Yobé River
that feeds Lake Chad.
8 Receding water levels have
disrupted fishing activities.
Out of the 33 fish species
caught in the 1960s,
only 3 remain.
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3
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5
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Water at the Heart of Science
8