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The most significant factor in the
spread of desert conditions is the long-term lack of rain.
After six or seven years without rainfall, any rain that finally
does come will simply wash away the soil. Trees cannot survive
without rain for more than seven years. Death of trees combined
with lack of rain will increase the spread of desertification.
Irregular rainfall is also a concern. An area may receive
sufficient annual rainfall, but in a relatively short period
of time. The land, particularly if it is already degraded,
will not absorb all the water, and the heavy rains will cause
flooding and water erosion.
It is not easy to determine how much desertification is caused
by rains or by poor farming methods combined with overgrazing.
However, it is generally believed that both contribute to
the problem.
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