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Figure 20: The world’s water resources will not change, but the
human population and its demands on supply are growing rap-
idly. Meeting these demands will require wise investment in how
we use and reuse our water (UN Water Statistics).
Figure 21: Increasing water scarcity with population increase.
The effects of climate change are exacerbated by the rapidly increas-
ing physical expansion of cities, deforestation and grazing of up-
lands surrounding cities, and the heavy build-up of infrastructure
and lack of green rain-absorbing vegetation and areas inside cities.
With extensive build-up of concrete, housing, roofs and roads in
cities, no ground and vegetation is available across larges areas to
absorb and slow the water, resulting in massive run-off and flood-
ing of cities (Nyenje et al, 2010), especially the low-lying slums.
How wastewater is treated can in turn have an impact on cli-
mate change. Wastewater and its treatment generates methane
and nitrous oxide and carbon dioxide. It is worth noting that
methane has an impact 21 times greater than the same
mass of carbon dioxide. Nitrous oxide is 310 times more
potent (AAEE, 2008). Although a relatively small contribu-
tor to global emissions, wastewater and its management
is a growing impact. Methane emissions from wastewater
are expected to increase almost 50 per cent between 1990
and 2020, while, estimates of global N2O emissions from
wastewater are incomplete they suggest an increase of 25
per cent between 1990 and 2020 (IPCC, 2007). There is a
pressing need to investigate and implement alternatives to
current wastewater treatment, which minimize the produc-
tion of greenhouse gases and power consumption.
Water Statistics
Population increase and water resources
Billion
2007 2050 2007 2050
Cubic kilometres
6.6
9.3
200 000 200 000
Water availability below 1 000 m3 per capita per year was regarded
as an indicator of water stress.
Projections for 2025 and 2050 are computed considering
socio-economic and climatic driving forces from the B2 scenario of
the IPCC.
Source: Joseph Alcamo, et al, Future Long-term changes in global water
resources driven by socio-economic and climatic changes, Hydrological
Sciences Journal, 52(2), April 2007.
Projection for
2050
2025
2007
World population living in river basins
with severe water stress
Million people
4 909
3 208
1 601