Fjölrit RALA - 05.12.1999, Blaðsíða 82

30
Desertification in Ethiopian highlands
with in the range of areas classified as prone to desertification are 112. Of the 112
weather stations in dry areas, 68 are located in areas above 1500 m a.s.l. and 38 sta-
tions are located in areas below 1500 m elevation.
The arid and hyper-arid areas in Ethiopia range in altitude between 0 and 1000 m
and get a range of annual rainfall from 28—406 mm. These two zones cover a land area
of 353,000 km2 and are used by nomadic pastoralist. Overgrazing, wind erosion, sa-
linity and deforestation are the major man induced causes for land degradation in
these zones. The semi-arid areas range in altitude between 625 and 2550 m a.s.l. and
receive a range of annual rainfall from 411-897 mm with corresponding potential
evapo-transpiration ranging from 1284-2138 mm per year. The semi-arid areas in
Ethiopia cover 207,000 km2 and are used by semi-sedimentary agro-pastoralist and
settled crop cultivators throughout the country. Poor farming practices, overgrazing,
deforestation, water and wind erosion, and salinity are the major man induced causes
for land degradation in this zone.
The dry sub-humid areas range in altitude between 1200 and 2700 m a.s.l. and re-
ceive a range of annual rainfall from 642-1117 mm with corresponding evapo-
transpiration from 1312-1790 mm per year. The dry sub-humid areas cover 300,000.
km2 and this zone is a major annual crop producing area where Oxen-plow cereal
mono-culture is a dominant farming system.
There are fairly large areas in the Ethiopian highlands (above 1500 m a.s.l.) prone
to desertification hazards and fall within UNEP’s defmition of desertification where
RR/PET<0.65 (Figures 1 and 2; Table 1). The land degradation process in the dry sub-
humid and semi-arid areas becomes very serious because it affects nearly 27 million
people and 116,000 km2 of cultivated land (64% of the country’s total cultivated land
area is located in this zone).
Soil moisture regime classification of Ethiopia
Soil moisture and temperature play major roles in controlling plant growth and devel-
opment. Large areas in Ethiopia are subjected to recurring droughts, low and erratic
rainfall, and frequent low available soil moisture. Reduced soil moisture increases soil
temperature which causes reduction in plant cover and binding ability of soil particles
and soil aggregates. This makes the soils susceptible to erosive forces.
The dryland areas in Ethiopia fall within ustic, xeric and aridic soil moisture re-
gimes. The total land area covered by these three zones is 860,000 km2 of which
106,000 km2 is cultivated. This area supports a total population of 27.1 million (Figure
2 and Table 5). Areas in Ethiopia receiving 300 mm annual rainfall cover 26.4 million
ha (22% of the total land area) and are classified in aridic soil moisture regime. There
is no cultivation in this zone and the land is only used as nomadic rangeland. This
zone is extremely sensitive to drought, salinity and alkalinity problems. Approxi-
mately 1.5 million nomadic people live in this zone. The major man induced causes
for desertification are overgrazing and deforestation.