Natural Hazards: Causes and Effects - Disaster Management Center ...

Slash-and-Burn Agriculture. This method of cultivation is typical of rainfed cropping in drylands;
with summer rain, the farmer will return to a particular plot after its vigor has been restored by
extended fallow, often as long as 20 years. Shortening the cycle, coming back too soon, can
have adverse effects on plant recovery and regrowth and on soil fertility. When this happens,
measures should be taken to restore the cycle to its older rhythm, perhaps by expanding the
area available to cultivation or by removing population pressures through resettlement or the
development of alternative livelihoods.
Making Fallow Periods Economically Feasible. In these systems, valuable substances, such as
gum arabic, can sometimes be extracted from the natural regrowth during the fallow part of the
cycle. Steps can be taken to increase the value of regrowth by introducing new trees or by
adopting good forestry practices.
Land Management
Once rainfed cropland has been degraded, efforts to rehabilitate it should form part of larger
actions directed toward water management, improved land use and the control of erosion.
Within broader plans, specific actions to be taken will depend on the course that desertification
has followed.
Gullying. This particularly unsightly form of erosion can be arrested by planting trees in upper
catchments and along gully margins and by planting grass in areas that feed the gullies with
flows. Also helpful are the construction of diversion banks and furrows across gully heads, and
the installation of check dams and silt traps along gully courses. Under favorable conditions,
gullies can simply be filled in and their banks replanted.
Sheet Erosion. This form of erosion, which scours topsoil from wide areas, can be countered
with contour banks and ditches, grass-covered contour strips, and terraces.
Wind Erosion. This form of erosion blows soil away from rainfed cropland and causes sand drift
and dune encroachment. It can be countered by planting shrubs and trees in shelter belts (at a
spacing four times as far apart as their eventual height). Fences can be constructed or lines of
resistant shrubs and trees planted as barriers against oncoming sand, upwind of threatened
areas. Bare sand can be covered with matting, bituminous coating or mulches of vegetation
litter.
Stabilizing Sand Surfaces. Sand surfaces can be stabilized by seeding and planting proper
successions of vegetation, including plants that thrive in sand in association with shrubs and
trees. This can be done easily by establishing greenbasins, a technique developed in Australia.
Greenbelts are created by building or ploughing small circular banks in a field to form a series of
basins. These trap windblown seeds and nourish them by trapping moisture and water to form
small temporary ponds. The embankments protect the seeds from dust storms, and the
moisture provides the nourishment to enable them to sprout. Greenbelts several kilometers
wide and hundreds of kilometers long are often built as a line-of-defense, much like a firebreak,
to prevent further encroachment of the desert. 7 In addition dunes can be leveled or reshaped to
remove slip faces while acting to prevent their reappearance.
Irrigation
Desertification of Irrigated Land. The amount of irrigated land lost annually to desertification
(some hundreds of thousands of hectares) is about equal to the amount of land newly brought
under irrigation each year. Large investments are involved in the breakdown and abandonment
of such intensive, highly capitalized agricultural projects. Irrigable land is scarce, and new