Geoscience Reference
In-Depth Information
Arid environments: their nature and extent
David S.G. Thomas
1.1
Geomorphology in arid environments
challenge. Even with the technological advances of the
late nineteenth and twentieth centuries that made travel
and existence in drylands possible for a greater range
of people, arid environments still provide major limita-
tions to the range and extent of human occupations and
activities.
European interest in arid environments grew from the
late eighteenth century onwards (Heathcote, 1983), usu-
ally associated with the quest for natural resources and
colonisation, or with attempts at religious conversion.
Much of the early 'Western' scientific knowledge con-
cerning such areas came not from specialist scientists but
from those whose primary goals were associated with
these activities. It has been noted or implied (see, for
example, Cooke and Warren, 1973; Cooke, Warren and
Goudie, 1993; Goudie, 2002) that early geomorphological
research in arid areas was dogged by excessive descrip-
tion, superficiality and secular national terminology. The
first characteristic, description, has often been criticised,
especially at times when quantification has been a cen-
tral paradigm in geomorphology. Yet description can be
an important prerequisite of rigorous explanation, analy-
sis and deeper investigation. This is no better illustrated
than by the work of Dick Grove and Ron Peel (e.g. Grove,
1958, 1969; Peel, 1939), where careful description of land
forms and landscapes preceded analysis and the quest for
geomorphic explanations of their development and the
controls on the processes that shaped them.
In the case of early works, the descriptive component
is hardly surprising. For European writers with temper-
ate world origins, desert landscapes must have repre-
sented spectacular, bizarre and unusual contrasts to the
plant and soil mantled landscapes of many of their home-
lands. Before early descriptive accounts are totally pillo-
ried, it should also be remembered that geomorphological
Aridity, a deficit of moisture in the environment, is a sig-
nificant feature of a large part of the Earth's land sur-
face. Aridity is complex, and its environmental manifes-
tations vary from place to place and through time, such
that its definition, occurrence and environmental con-
sequences are complex and require careful unravelling.
Aridity is also complex and challenging for many life
forms, since moisture is such a fundamental requirement
for many. Aridity does not simply equate with the concept
of deserts, and goes far beyond what are widely regarded
as such, so that there is a great diversity within, and be-
tween, arid environments. The purpose of this topic is to
provide explanations for the diversity and nature of arid
environments, through an exploration of the land-shaping
processes that operate within them.
For much of history and for many human races, arid
environments have been areas to avoid, though for those
that have been, and continue to be, resourceful and able
to adapt, arid regions have proved to be environments
that can be effectively and successfully utilised. Lack of
surface water, limited foodstuffs and climatic extremes
have generally made arid areas unfavourable places for
habitation, though for resourceful hunter-gatherer and
pastoral-nomadic peoples, living at low population den-
sities, these environments have proved to be places of
opportunity. In other contexts, the apparent scarcity of
key resources may have driven innovation: it is perhaps
no coincidence that early civilisations, in Mesopotamia,
in Egypt and in parts of central Asia, developed strate-
gies to cope with aridity, with early agriculture develop-
ing, c.4000 years ago, in the Mesopotamian heartland.
However, for populations from more temperate and bet-
ter watered regions, aridity has often proved a significant
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