Water scarcity and abundance, water productivity and their relation to poverty - Water Scarcity, Livelihoods and Food Security - page 18

scarcity and withdrawal is less than 25 percent (Molden, 2007). High levels of
water use lead to closed basins, that is, where water no longer flows out
through the rivers. The Yellow River in China failed to reach the sea in 1997
for 226 days and was dry to 600 km upstream (Ringler et al., 2012).
Subsequent government action reduced water use for irrigation and this helped
provide year-round flows, which, however, were still insufficient to counter
entry of sea water within the basin, leading to damage of wetlands. The
Karkheh in Iran is potentially closed by the use of its limited water for
irrigation downstream of the new dam to the detriment of the Hoor-al-Azim
wetlands on the border with Iraq (Ahmad and Giordano, 2012).
By these definitions, only two of the CPWF's ten basins, the Limpopo and
the Yellow, suffer from physical water scarcity, although parts of the Ganges
and the Karkheh have scarcity at times in specific places.
Both population size and availability of blue water affect water scarcity, and
both are captured by the Falkenmark water stress indicator (Falkenmark, 1997)
and can be applied to basins, countries or regions. Water stress occurs when
there are less than 1700 m 3 /yr of renewable water resources per capita for all
needs. When per capita supply falls below 1000 m 3 /yr there is water scarcity ,
and below 500 m 3 /yr, absolute scarcity . The indicator has great spatial variability,
across continents, within river basins, across and within countries. It falls faster
where population growth is rapid. The Yellow (1250) is stressed, the Karkheh
(1970) and the Volta (2560) approach stress, but even the populous Indus-
Ganges (5900) is over three times the level that indicates stress. The other
basins exceed 10,000 (the São Francisco is the highest at 38,390). In the future,
many more people are likely to experience water stress and water scarcity,
especially in sub-Saharan Africa and South Asia (Figure 2.1) (UNDP, 2006).

Population of countries facing water or scarcity
(billions)

2.5

Water scarcity: less than 1,000 m 3 /yr per capita

Water stress: less than 1,700 m 3 /yr per capita

2.0

1.5

1.0

0.5

0.0

1990
South Asia

2005 2025 2050 1990

Sub-Saharan
African

2005 2025 2050 1990

Arab States

2005 2025 2050 1990

East Asia and
the Pacific

2005 2025 2050 1990

Latin America and
the Caribbean

2005 2025 2050

Figure 2.1 Water stress is projected to accelerate in intensity in several regions.
Source: UNDP, 2006.