Large river basins
Fresh water
represents
3% of the water
on the planet.
Lakes and rivers
from rain, groundwater and melting
glaciers drains to a body of water, such
a sea, an ocean or a lake. The river basin
bears the name of its main river,
a watercourse fed by several tributaries
as it moves downstream.
Which is essential for people to survive
and for societies to develop, but fresh
water is unevenly distributed across
the planet.
The largest reserves are found in
the tropical regions, where more rainfall
occurs. Precipitation and therefore
watercourse discharge can vary
significantly within one river basin.
This is the area in which water coming
There exist river basins in all shapes
and sizes, being the Amazon, the Congo,
the Mississippi and the Nile the largest
watersheds.
are resources
easily used
1
4
by humans
and represent
only 1-2% of this
fresh water.
5
PACIFIC
OCEAN
6
2
MAJOR
RIVER BASSINS
ON EARTH
3
11
9
ATLANTIC
OCEAN
10
8
7
EAST
CHINA SEA
INDIAN
OCEAN
6. Niger
Basin area: 1.2 million km².
Average discharge: 5,600 m3/s.
Length: 4,184 km.
1. Mississippi
Basin area: 3.2 million km².
Average discharge: 13,000 m3/s.
Length: 3,780 km.
7. Congo
Basin area: 3,5 million km².
Average discharge: 40,000 m3/s.
Length: 4,700 km.
2. Orinoco
Basin area: 1 million km².
Average discharge: 35,000 m3/s.
Length: 2,140 km.
8. Nile
Basin area: 3 million km².
Average discharge: 2,800 m3/s.
Length: between 6,400 and 6,700 km.
3. Amazon
9. Ganges-Brahmaputra
Basin area: 6 million km².
Average discharge: 206,000 m3/s.
Length: between 6,300 and 6,800 km.
Basin area: 1.5 million km².
Average discharge: 30,800 m3/s.
Length: 2,896 km.
4. Rhône
10. Mekong
Basin area: 0.1 million km².
Average discharge: 1,700 m3/s.
Length: 810 km.
Basin area: 0.8 million km².
Average discharge: 21,000 m3/s.
Length: 4,350 km.
5. Danube
11. Yangtze
Basin area: 0.8 million km².
Average discharge: 6,300 m3/s.
Length: 3,020 km.
Basin area: 2 million km².
Average discharge: 30,000 m3/s.
Length: 6,380 km.
DID YOU KNOW?
The Nile and the Amazon have almost
the same length, around 6,700 km.
However, the Amazon, with a larger
basin and more abundant rainfall,
is considerably more powerful, with
an average discharge 25 times higher.
Lakes and rivers are essential
for human
communication
2
Changing rivers
Rivers are not
fixed in time
and space.
There are subtle
links between
watercourses and
the reliefs in which
Water always flows down the steepest
slope. Therefore a river’s natural flow
is linked to the topography, which in turn
constitutes the legacy of the basin’s
geological history.
But water creates landscapes,
by dissolving rocks and transporting them
downstream in the watercourse. As a result
rocks, pebbles, sand and silt produced
by this erosion are deposited and build up
on the river bed and banks, disturbing
and diverting the river’s flow. Extreme
climate events, such as drought or heavy
Ecuador
rainfall, accelerate erosion and thus
increase transport of material affecting
as a consequence the watercourses.
Since the 19th century, humans have
changed rivers significantly. These changes
reroute branches, alter banks, reduce and
disturb the river flows, create reservoirs,
alter water flows and disrupt the wildlife
living within the watercourses. But they also
bring benefits to people supplying water
to the towns and fields, producing energy,
creating leisure areas, etc.
Spain
France
they evolve.
But they have
been profoundly
and rapidly
affected by the
climate change,
and significantly
The Pastaza River valley.
A torrential in steep mountainous regions
and becomes wider, deeper and slower
downstream in the lowlands.
Aldeadávila Dam.
Reservoirs created by dams are used
to provide towns and cities with water
and energy and to irrigate fields.
Many projects for large dams
on tropical rivers have been planned.
Bolivia
Thermal (or nuclear) power plants use
rivers for cooling. The subsequent
increase of the water temperature
by 2 to 3 °C disrupts river ecosystems.
Morocco
Russia
by the changes
made by humans
over the last
200 years.
A glacier on the Huayna Potosí Mountain.
The Glaciers in Colombia, Ecuador, Peru and
Bolivia that feed the Andean watercourses
have been reduced from 30% to 50% since
the late 70s confirming the acceleration
of climate change at the end of the
20th century in this part of the world.
River Lena.
When a river is divided into several
channels, some are only fed during floods,
while others are cut off from the river
for ever, but still contain water and have
a rich biodiversity.
The effects of climate change vary over time,
experiencing extreme drought in one year
and heavy flooding the next, but they also
vary in space, with lack of rain in one area
and at the same time heavy rains in another.
DID YOU KNOW?
Some rivers have been evolving for millions
of years making impressive changes to
landscapes, digging their beds deep into the
rock; as is the case of the Colorado River in
the United States which has been ‘sculpting’
the Grand Canyon for 7 million years.
The meanders evolve
as a result of erosion and sedimentation
caused by the current
3
Global warming:
the facts
According
to the IPCC*, the
Earth’s average
temperature
Without quick and effective changes
to greenhouse gas emissions, the global
temperature will undergo an average
increase of 3.7°C to 4.8°C by 2100.
The international community’s aim
is to do all it can to limit this increase to 2°C,
a challenge considered as possible
according to the experts. The consequences
of increasing the average temperature
are multiple. They include changes
to rainfall patterns, with more frequent
extreme events, both extreme rainfall
and drought, causing floods and severe
low water levels in practically all major
river basins in both temperate
and tropical regions.
since 1880
has increased
by 0.85°C.
It is «extremely
likely» that most
CO2 is by far the most problematic
greenhouse gas, accounting for 76%
of emissions. Its principal sources
are energy production, agriculture,
industry and transportation.
Industry has grown enormously since 1950,
and the corresponding temperature increase
is the largest ever recorded: +0.6°C.
If we look at Earth’s average temperature,
there is only a 5°C difference between ice ages
and warm periods, when polar ice caps
were almost no existed.
of this increase
is due to human
activities**.
Intergovernmental Panel
on Climate Change.
*
**
2013-2014 report.
If the greenhouse gas effect is not reduced by at least
40% by 2050, scientists predict serious consequences.
Based on the worst case scenario, in India and in Bangladesh,
the monsoon rains causing floods, will increase approximately 20% in 2100,
and a century later more than 50 %.
On the other hand, the Mediterranean basin, the Sahel, Southern Africa
and a part of the Amazon region the rainfall will decrease 10% to 20% in 2100,
and even more than 50% by 2200.
In France, climate change could reduce watercourse
discharge from 20% to 30% by 2050, with longer
and more frequent droughts.
DID YOU KNOW?
Under the +4.8°C scenario, rivers,
lakes and wetland areas will be
adversely affected by the full force
of climate change. Reduced water
supplies would lead to further
competition between the four main
uses of water: domestic, agricultural,
industrial and environmental.
Desertification threatens 40%
of the planet’s land surface, affecting
110 countries, particularly in Asia
and Africa
4