Chapter 10
The arid zones
1. Introduction
The arid regions are areas of scarce precipitation and as a consequence the vegetation
cover is reduced or nonexistent (Figure 10.1). They present a variable distribution, due to
their location in high- and low- latitude areas, in the inner part of continents and littoral
zones and also in zones of high altitude. Cold deserts in medium latitudes produce a
particular problem, different to those in warm zones, because they are affected by the
activity of periglacial processes.
The exploration of many of the arid regions is related to colonisation by Europeans of
these areas, as they searched for new natural resources. The times of this exploration were
highly variable and are basically circumscribed by modem and contemporary times. The
first documents known are of a general character and they emphasise geographical and
naturalistic aspects. At end of the 19th century the first geomorphological works of great
scientific rigor were carried out, such as those made by Gilbert, Powell, and Dutton in their
study of the deserts of the southwest United States. Despite these precedents, however, the
studies have been generally of a descriptive character with the use of local terms, which
has produced a certain confusion of ideas among geomorphologists. In the late 20th
century with the advent of dynamic geomorphology, which analysed geomorphic
processes by means of the application of physical and chemical techniques to explain
existing forms, there has been a considerable advance in the knowledge and evolution of
landforms of the arid zones.
The geologic, climatic and vegetation characteristics of warm desert environments are
highly variable (Goudie, 2002). These overlay geologic formations of different
composition and age, with a full landform stability or, to the contrary, with a marked
neotectonic activity. The climates of deserts are quite variable and characterised generally
by scarce precipitation and high temperatures with a great daily amplitude. Vegetation is
sparse or nonexistent but well adapted to the high range of temperatures. They
fundamentally obtain water through their roots, which can penetrate up to 20 m deep
(Nicholson, 1993).
On the other hand, desert environments are not suitable conditions for humans due to
the extreme climates and the scarcity or absence of water and food. Human behaviour in
these areas varies from place to place, because in some places zones of population are
lacking and others, on the contrary, are densely populated. It is important to note that 15%
of the worldwide population lives in these regions (Heathcote, 1983). Moreover, the
growth of the population is very important in many of these zones, with increments of 50%
or more in the last 50 years. It was calculated that the population would reach 1200 million
by the year 2000. Therefore, the use by humans of scarce hydric and vegetable resources
The arid zones
1. Introduction
The arid regions are areas of scarce precipitation and as a consequence the vegetation
cover is reduced or nonexistent (Figure 10.1). They present a variable distribution, due to
their location in high- and low- latitude areas, in the inner part of continents and littoral
zones and also in zones of high altitude. Cold deserts in medium latitudes produce a
particular problem, different to those in warm zones, because they are affected by the
activity of periglacial processes.
The exploration of many of the arid regions is related to colonisation by Europeans of
these areas, as they searched for new natural resources. The times of this exploration were
highly variable and are basically circumscribed by modem and contemporary times. The
first documents known are of a general character and they emphasise geographical and
naturalistic aspects. At end of the 19th century the first geomorphological works of great
scientific rigor were carried out, such as those made by Gilbert, Powell, and Dutton in their
study of the deserts of the southwest United States. Despite these precedents, however, the
studies have been generally of a descriptive character with the use of local terms, which
has produced a certain confusion of ideas among geomorphologists. In the late 20th
century with the advent of dynamic geomorphology, which analysed geomorphic
processes by means of the application of physical and chemical techniques to explain
existing forms, there has been a considerable advance in the knowledge and evolution of
landforms of the arid zones.
The geologic, climatic and vegetation characteristics of warm desert environments are
highly variable (Goudie, 2002). These overlay geologic formations of different
composition and age, with a full landform stability or, to the contrary, with a marked
neotectonic activity. The climates of deserts are quite variable and characterised generally
by scarce precipitation and high temperatures with a great daily amplitude. Vegetation is
sparse or nonexistent but well adapted to the high range of temperatures. They
fundamentally obtain water through their roots, which can penetrate up to 20 m deep
(Nicholson, 1993).
On the other hand, desert environments are not suitable conditions for humans due to
the extreme climates and the scarcity or absence of water and food. Human behaviour in
these areas varies from place to place, because in some places zones of population are
lacking and others, on the contrary, are densely populated. It is important to note that 15%
of the worldwide population lives in these regions (Heathcote, 1983). Moreover, the
growth of the population is very important in many of these zones, with increments of 50%
or more in the last 50 years. It was calculated that the population would reach 1200 million
by the year 2000. Therefore, the use by humans of scarce hydric and vegetable resources