Environmental Engineering Reference
In-Depth Information
10.1
INTRODUCTION
The semi-arid regions of the planet are more com-
monly occupied and more intensively managed than
the arid areas, but all are vulnerable to ecosystem dete-
rioration or desertifi cation. A review of desertifi cation
risk in 2001 suggested the vulnerability classes and
estimates of area involved and population at risk as
given in Table 10.1 .
Many of the more extreme desert areas are rarely
used, although indigenous people in the past survived
in some of them (Figure 10.1). It is important to
remember these past uses by people because they often
shaped the ecosystems we see today (Nabhan
et al
.
1982). Often, areas in the transition zones between
arid and semi-arid regions are used by people only
during wet periods (Felger & Moser 1985). Some of the
most severely damaged areas are
abandoned
after
their usefulness declines through over-exploitation (see
Chapter 2). The lands at risk of desertifi cation should
be further categorized by current and historic use,
current condition and tenure (ownership or use rights),
but this has not been done in a systematic manner.
Despite many similarities, the challenge of desertifi ca-
tion can be very different from one region to the next,
and perhaps even from one valley to the next.
In this chapter, I attempt a comprehensive approach
to restoration that explicitly examines the socio-
economic drivers that create unsustainable pressures
on arid lands in addition to nonhuman drivers. In
addition, I develop a
holistic approach
to restoration
considering the people that are most affected by deser-
tifi cation. The goal is to integrate the best practices
from past societies and cultures around the world that
have addressed similar problems, with the latest fi nd-
ings from research and development on more sustain-
able ecological, technical and political or economic
solutions (Bainbridge 2007a). A key aspect of this
effort is to understand these problems well enough to
Arid and semi-arid lands occur in areas where climatic
conditions create water limitations and the water lost
through evaporation exceeds the water gained from
precipitation (Bailey 1996). Truly arid regions are
called deserts, and they may be cold, temperate or hot,
but all are relatively very dry. Defi nitions vary, but
areas with annual precipitation of 25 cm or less are
often considered as deserts. Semi-arid regions, often
called steppes, typically surround or occur adjacent to
deserts, but may also occur in isolation. The severe
water limitations and climatic extremes that prevail in
these regions render arid and semi-arid regions vulner-
able to disturbance and very slow to recover (United
Nations Environment Programme (UNEP) 1992;
Aronson
et al
. 2002 ; Bainbridge 2007a ). In other
words, they have less
resilience
and
resistance
than
most other
biomes
.
Arid and semi-arid lands make up approximately
40% of the Earth's continental surface and are home
to more than 2 billion people (Adeel
et al
. 2005 ). Many
of these are city dwellers, but ecosystem deterioration
in the rural drylands - a common shorthand term for
arid and semi-arid lands - is widespread and getting
worse. Approximately 250 million people at present
are affected by the loss of productivity from
degrada-
tion
of ecological resources or
desertifi cation
, while
as many as 1.2 billion people will be affected in the next
few decades (Randriamiarina 2009). This will lead to
increased suffering, growing numbers of environmen-
tal refugees and regional and international migrations
that will no doubt cause civil unrest and turmoil (Sachs
2007). Half of the dryland dwellers earn very little
money and as they live with very limited resources they
are very vulnerable to unforeseeable events and slow-
moving processes (Dobie 2001).
Table 10.1
Estimates of land area considered vulnerable and corresponding numbers of impacted human populations.
Note: The global population density map is limited to latitudes 72°N to 57°S. Not all vulnerable lands are arid and semi-arid
lands. After Eswaran
et al
. (2001) .
Vulnerability
class
Area subject to desertifi cation
Population affected
Million km
2
% global land area
Millions
% global population
Low
14.60
11.2
1085
18.9
Moderate
13.61
10.5
915
15.9
High
7.12
5.5
393
6.8
Very high
7.91
6.1
255
4.4
Total
44.24
34.0
2648
44.0
