Geography Reference
In-Depth Information
FIGURE 12.14
Owens Valley, California. The city of Los Angeles depends heavily on mountain water
resources that have to be conducted over great distances. (Photo by P. Walther.)
It is not only in dry parts of the world that mountain water is essential to life and
economies. Even in temperate humid areas, mountain water contributes 30-60 percent
of the water flowing to the lowlands (Viviroli et al. 2003). The Alps cover only 23 per-
cent of the area of the Rhine River basin, but they provide half the total flow over the
year, varying from 30 percent in winter to 70 percent in summer. It is only in the humid
tropics, where the lowlands receive at least 1,500 to 2,000 mm (600 to 800 in.) of an-
nual precipitation, that the contribution of water from mountain areas is insignificant.
Yet it should be noted that, in spite of the apparent accuracy of the figures cited above,
our knowledge of the amounts and distribution of precipitation falling in, and the runoff
deriving from, mountain areas around the world remains rather inadequate, especially
in developing countries. At regional to global scales, this problem is exacerbated by the
lack of availability of much of the data collected at national levels (Viviroli et al. 2007).
HARVESTING MOUNTAIN WATER
While most mountain water is used for lowland agriculture, it is also vital for mountain
agriculture.
Irrigation systems
are found in mountain areas around the world, storing
water and directing it to fields at the right time and place to allow crops to grow and
optimize yields. The simplest systems involve blocking streams and allowing the wa-
ter to flood over meadows, as for traditional hay meadows in the Alps (Netting 1981).
More complex systems involve constructing channels to bring water from high springs
and streams to the fields. These systems—such as the bisses of Valais in the Swiss Alps
(Crook and Jones 1999) and the channels in the Pamir in Tajikistan and of the Pokot
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