The human impact - Arid Zone Geomorphology - page 564

impact. It is also possible that arroyo incision occurred be-
cause a natural geomorphological threshold was crossed;
after a period of relative stability in valley floors gullying
was inititated by some triggering event.
Of course, the true explanation of arroyo incision in the
US southwest during the late nineteenth and early twen-
tieth centuries may involve any one of these competing
theories - or indeed more than one, because they are not all
mutually incompatible. The example serves as a reminder
of the complexity of the natural world, a complexity that
becomes greater still when the possible effects of people
are added.

Babaev, A.G. (1999) The natural conditions of central Asian
deserts, in Desert Problems and Desertification in Cen-
tral Asia (ed. A.G. Babaev), Springer-Verlag, Berlin,

pp. 5-20.
Bahre, C.J. (1991) A Legacy of Change , The University of Ari-
zona Press, Tucson, Arizona.
Barbier, N., Couteron, P., Lejoly, J. et al. (2006) Self-organized
vegetation patterning as a fingerprint of climate and human
impact on semi-arid ecosystems. Journal of Ecology , 94 ,
537-547.
Bingham, F.T., Rhoades, J.D. and Keren, R. (1985) An applica-
tion of the Maas-Hoffman salinity response model for boron
toxicity. Journal of the Soil Science Society of America , 49 ,
672-674.
Blackburn, W.H., Knight, R.W. and Schuster, J.L. (1982)
Saltcedar influence on sedimentation in the Brazos River.
Journal of Soil and Water Conservation , 37 , 298-301.
Boroffka, N., Oberhansli, H., Sorrel, P. et al. (2006) Archaeology
and climate: settlement and lake-level changes at the Aral
Sea. Geoarchaeology , 21 , 721-734.
Brandt, S.A. (2000) Classification of geomorphological effects
downstream of dams. CATENA , 40 , 375-401.
Bruins, H.J., Evenari, M. and Nessler, U. (1986) Rainwater-
harvesting agriculture for food production in arid zones:
the challenge of the African famine. Applied Geography ,
6 , 13-32.
Butler, D.R. (1995) Zoogeomorphology: Animals as Geomor-
phic Agents , Cambridge University Press, Cambridge.
Butler, D.R. (2006) Human-induced changes in animal popula-
tions and distributions, and the subsequent effects on fluvial
systems. Geomorphology , 79 , 448-459.
Butzer, K.W. (1976) Early Hydraulic Civilization in Egypt:
A Study in Cultural Ecology , University of Chicago Press,
Chicago.
Caldwell, T.G. McDonald, E.V. and Young, M.H. (2006) Soil
disturbance and hydrologic response at the National Training
Center, Ft. Irwin, California. Journal of Arid Environments ,
67 , 456-472.
Chin, A. (2006) Urban transformation of river landscapes in a
global context. Geomorphology , 79 , 460-487.
Choun, H.F. (1936) Dust storms in southwestern plains area.
Monthly Weather Review , 64 , 195-199.
Cooke, R.U. and Reeves, R.W. (1976) Arroyos and Environ-
mental Change in the American Southwest , Clarendon Press,
Oxford.
Cooke, R.U., Brunsden, D., Doornkamp, J. and Jones, D.
(1982) Urban Geomorphology in Drylands , Oxford Univer-
sity Press, Oxford.
Critchley, W.R.S., Reij, C. and Willcocks, T.J. (1994) Indige-
nous soil and water conservation: a review of the state of
knowledge and prospects for building on traditions. Land
Degradation and Rehabilitation , 5 , 293-314.
Elliott, J.G., Gellis, A.C. and Aby, S.B. (1999) Evolution of
arroyos: incised channels of the southwestern United States,
in Incised River Channels: Processes, Forms, Engineering,
and Management (eds S.E. Darby and A. Simon), John Wiley

22.6 Conclusions

People have lived in deserts for a long time and have
always had some influence over desert landforms and
processes. These impacts have been both deliberate and
inadvertent, the former being more easily assessed than
the latter. The scale of human impact has undoubtedly
grown with the rise in numbers of people living in desert
areas, although this is not to say that impacts are predom-
inantly recent nor that change in geomorphology cannot
be induced by small numbers of people.
The human impact on desert geomorphology is cer-
tainly diverse and widespread. However, our understand-
ing of cause and effect is not always clear and the difficul-
ties of distinguishing between the effects of variability in
purely natural geophysical drivers of change and human-
induced drivers will certainly continue. Indeed, distinc-
tions between the two are likely to become even more
blurred as we grapple with changes wrought by global
climate change possibly effected in part by human society
(see Chapter 24). None the less, the division will continue
because human actions represent the one set of driving
forces for change that we can control in a predictable
way. This truism is important not least because of the fre-
quent negative feedbacks societies experience in the form
of geomorphological hazards (see Chapter 23).

References

Abrol, I.P., Yadav, J.S.P. and Massoud, F.I. (1988) Salt-affected
soils and their management. FAO Soils Bulletin , 39 .
Allsopp, N., Gaika, L., Knight, R. et al. (2007) The impact of
heavy grazing on an ephemeral river system in the succu-
lent karoo, South Africa. Journal of Arid Environments , 71 ,
82-96.
Anton, D. (1982) Modern eolian deposits in the eastern province
of Saudi Arabia, in Abstracts of the Eleventh International