Geoscience Reference
In-Depth Information
then from Spain as far as Mexico some 500 years ago (Evenari et al.,
1971
). The laws
governing the use of water from the
foggara
date back more than 2,000 years and are
still strictly applied in the remote settlements of the Algerian Sahara (Kobori et al.,
1982
). The importance of water and its careful distribution in desert settlements in
North Africa and the Middle East is reflected in the many hundreds of Arabic words
in current use for wells, water containers and methods of collecting water. Nutuhara
(1982) recorded Syrian desert villagers using some 350 words relating to water, 70 to
water quality, 200 to rain and clouds, 190 to valleys, 140 to pastures, 290 to wells
and cisterns, and 110 to ropes as parts of a well. The San people of the Kalahari have
a similarly rich vocabulary in regard to hunting and plant food gathering (Tanaka,
1976
).
Another method of harvesting water concerns the use of piles of boulders to collect
dew. Evenari et al. (
1971
) were doubtful that humans in the Negev Desert 2,000 years
ago could derive much benefit from dew. However, a later reappraisal by Jacqueline
Pirenne has shown that dewwas an important historic resource for humans and animals
in North Africa, the Red Sea coast and islands, Ethiopia, Arabia and theMediterranean
region. She noted that the 'Grand Clapier' in Haute Provence, southern France, which
is very dry in the summer, provides 270 litres per hour of water, equivalent to the
flow from a kitchen tap (Pirenne,
1977
, p. 135). This feature is a ridge of limestone
blocks and is 400 m long and 7-15 m wide. The aim of these and other piles of rocks
is to allow water vapour to condense on the surface of the stones at night when the
temperatures drop down to dew point, that is, 100 per cent relative humidity. The
resulting dew then trickles down the face of the rocks and may be captured in small
cisterns or may moisten the underlying soil enough to allow some plant growth. In
Tigray Province in northern Ethiopia, farmers lead their flocks out before dawn during
the dry season to allow them to graze on pastures soaked in dew. Needless to say,
other desert creatures benefit from the early morning dew, including birds, lizards
and gazelles. In north-west Australia, the irregular mound surfaces of one species
of termite trap moisture from dew and were once a resource for Aboriginal people
during travel ('walkabout'). The seeds collected by ants and termites and stored in
their mounds are still a famine food across the drier parts of Africa, as indeed, are the
insects themselves (Gast,
2000
).
The long-term adaptations of our prehistoric human ancestors to progressive desic-
cation and replacement of forest by grassland deserve to be mentioned here. The
possible interactions between human evolution and the spread of savanna grasslands
in Africa have long provoked interest and controversy. In 1925, Raymond Dart pro-
posed that the expansion of African savanna grasslands in the late Tertiary/Cenozoic
may have contributed to the development of an upright posture and bipedal gait in the
early hominid that he named
Australopithecus africanus
(Dart,
1925
). This 'savanna
hypothesis' has been much debated ever since. A recent study by Cerling et al. (
2011
)
of the carbon isotopic ratios (see
Chapter 7
) measured on soil carbonate nodules
