Geoscience Reference
In-Depth Information
Local tradition has it that the gullies only began to develop after clearing of the native
vegetation during the British occupation, which seems plausible.
Another very effective method widely used on steep hill slopes in the drylands of
South America, Africa, the Middle East and Asia is terracing. Provided the terraces
are well-constructed and well-maintained, and some natural fertilizer is returned to the
soils, the fields behind the terraces can be cultivated for centuries, or even millennia,
as in parts of the Negev Desert highlands in southern Israel and along the flanks of
Jebel Marra volcano in western Sudan. Some of the deepest and most spectacular
gullies in the world are those entrenched into the highly erodible loess soils of central
China. Here the central government co-opted local peasant labour for one month each
year to construct new terraces and repair damaged ones - a laborious task but one
acknowledged somewhat grudgingly by the local people as necessary.
Minimum tillage is another approach to preserving some form of surface cover
throughout the year in order to avoid the exposure of bare soil to erosion from
raindrop impact and run-off. Although the yields from cereal crops in wet years may
not be as high as they are when the stubble is burnt and pesticides and herbicides
are applied to eliminate weeds and pests, they remain relatively stable during both
wet and dry years, because the soils retain a larger stock of water beneath the stubble
mulchthantheydowhenbare.
Central to all effective land use is the need for an effective exchange of informa-
tion between farmers and agricultural extension officers. One initiative developed in
Australia three decades ago and still active is the
Landcare
movement, which at its
most successful allows new ideas and techniques to be widely disseminated among
farming communities about how to improve agricultural yields while maintaining or
enhancing soil fertility on a long-term basis (Campbell and Siepen,
1994
). Another
effective approach to achieving sustainable land use in arid areas is the provision
of accurate and timely information about the likelihood of above- or below-average
rainfall in order to allow farmers to plan their sowing and harvesting dates more stra-
tegically (Boyd et al.,
2013
). Given a suitable farming environment, crop modelling
software packages are another useful way of developing probabilistic scenarios about
the potential impact of possible future changes in climate and in climate variability
on crop yields (Luo et al.,
2007
; Luo et al.,
2010
).
At a regional scale, it is often helpful to be able to predict the possible impact
of future climate change by extrapolating from long-term trends in temperature and
rainfall and by using a modified version of the type of risk magnitude and frequency
matrix that is dear to the hearts of occupational health and safety officials and was long
used in the insurance industry. The aim here is to assess vulnerability of particular
natural resources to future change by considering exposure to risk, sensitivity, potential
impact and adaptive capacity (Bardsley,
2006
), using a qualitative scale from low to
high, much as the one used in
Table 26.2
in relation to soil erosion hazards and risks
in arid lands.
