Geoscience Reference
In-Depth Information
1994
; Kassas,
1995a
; Williams and Balling,
1996
; Williams,
2000
; Williams,
2002b
;
UNEP 2002a; UNEP, 2002b; Imeson,
2012
).
Desertification was for some years defined by the United Nations Environment
Programme (UNEP) as 'land degradation in arid, semi-arid and dry subhumid areas
resulting
mainly from adverse human impact
' (UNEP
1992a
, italics added), but since
June 1992 it has been redefined as 'land degradation in arid, semi-arid and dry
subhumid areas resulting from
various factors including climatic variations and
human activities
' (UNEP,
1992b
, italics added). This definition of the climatic areas
involved excludes the hyper-arid regions such as the Sahara and the Atacama deserts,
but it does comprise about 40 per cent of the land area of the globe, including significant
parts of Eurasia, Africa, Australia and the Americas.
The currently accepted definition was the one agreed upon at the United Nations
Conference on Environment and Development (UNCED), which was held in Rio de
Janeiro in June 1992 and popularly known as the Earth Summit (UNCED,
1992
). In
contrast to the superseded UNEP definition, which stressed human mismanagement
and ignored any influence of climatic variations, the 1992 UNCED definition took
into account climatic fluctuations, especially prolonged droughts. The main reason
for this change in perception was the impact of the severe 1968-1974 drought in the
Sahel region, which first became apparent along the south-western margins of the
Sahara and spread progressively eastwards to Ethiopia and Somalia, causing many
tens of thousands of deaths from starvation when the harvests from rain-fed agricul-
ture failed. (
Sahel
is an Arabic term for 'shore', and it refers geographically to the
region bordering the southern Sahara, including countries such as Mali, Niger and
Chad.) This prolonged drought, which was to persist with only minor interruptions for
nearly thirty years (
Chapter 23
), stimulated renewed scientific interest in the causes
of severe droughts and revealed very starkly how a sustained lack of rain can con-
tribute to widespread land degradation. At the International Geophysical Conference
in Grenoble in August 1975, French hydrologists and meteorologists drew attention
to the impact of this drought. Two years later, growing concern over water shortages
and land degradation prompted the United Nations to host a Water Conference in
Argentina in March 1977.
Five months later, UNEP organised a United Nations Conference to Combat Deser-
tification at the UNEP headquarters in Nairobi, at which a number of attempts were
made to define the elusive concept of 'desertization', or the spread of desert-like con-
ditions (United Nations,
1977
; United Nations,
1978
;Glantz,
1987
; Williams,
2002b
).
One suggestion was to restrict the meaning to denote the extension of such conditions
into semi-arid areas only, defined as areas in receipt of 50-300 mm of rain a year.
Others argued that areas of higher rainfall should be included, a view endorsed by
UNEP, so 'desertization' was defined as 'the spread of desert-like conditions in arid
or semi-arid areas up to 600 mm, due to man's influence or climatic change' (United
Nations,
1977
;Glantz,
1987
). Later workers ignored the climatic factor, and some
