Population increase and water resources Billion

Cubic kilometres 9.3

World population living in river basins with severe water stress

Projection for 2050

2025 3 208 6.6 200 000 200 000 1 601 2007

Million people 4 909

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.

2007 2050 2007 2050 Source:UN Water Statistics

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).

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

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.

Figure 21: Increasing water scarcity with population increase.

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.

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