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| Titel |
Influence of land use on rainfall simulation results in the Souss basin, Morocco |
| VerfasserIn |
Klaus Daniel Peter, Johannes B. Ries, Ali Ait Hssaine |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250076043
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| Zusammenfassung |
| Situated between the High and Anti-Atlas, the Souss basin is characterized by a dynamic land
use change. It is one of the fastest growing agricultural regions of Morocco. Traditional
mixed agriculture is replaced by extensive plantations of citrus fruits, bananas and vegetables
in monocropping, mainly for the European market. For the implementation of the land use
change and further expansion of the plantations into marginal land which was former
unsuitable for agriculture, land levelling by heavy machinery is used to plane the fields and
close the widespread gullies. These gully systems are cutting deep between the plantations
and other arable land. Their development started already over 400 years ago with the
introduction of sugar production. Heavy rainfall events lead to further strong soil
and gully erosion in this with 200 mm mean annual precipitation normally arid
region. Gullies are cutting into the arable land or are re-excavating their old stream
courses.
On the test sites around the city of Taroudant, a total of 122 rainfall simulations were
conducted to analyze the susceptibility of soils to surface runoff and soil erosion under
different land use. A small portable nozzle rainfall simulator is used for the rainfall
simulation experiments, quantifying runoff and erosion rates on micro-plots with a
size of 0.28 m2. A motor pump boosts the water regulated by a flow metre into the
commercial full cone nozzle at a height of 2 m. The rainfall intensity is maintained at
about 40 mm h-1 for each of the 30 min lasting experiments. Ten categories of
land use are classified for different stages of levelling, fallow land, cultivation and
rangeland.
Results show that mean runoff coefficients and mean sediment loads are significantly
higher (1.4 and 3.5 times respectively) on levelled study sites compared to undisturbed sites.
However, the runoff coefficients of all land use types are relatively equal and reach high
median coefficients from 39 to 56 %. Only the rainfall simulations underneath mandarin trees
in a plantation show with 10 % low coefficients. The results are stronger differentiated for the
sediment loads. On levelled areas, the simulations reach median sediment loads of 41 and 61
g m-2 respectively. In spite of high runoff coefficients, the lowest sediment loads of
around 4.5 g m-2 are measured on old fallow land (>5 y.) and rangeland which are
both protected by biological crusts. The same low result is found on the mandarin
plantation. On other younger fallow land (1-2, 2-5 y.) as well as on stone covered
badlands and sundry anthropogenic influenced soils medium soil losses between
18 and 25 g m-2 are reached. On sparsely vegetated grain fields, soil erosion is
because of initiated crusting despite lower runoff coefficients with 30 g m-2 still
high.
Land-levelling measures have the greatest influence on rainfall simulation results.
Although runoff coefficients on almost all land use types are similar, clear differences of soil
erosion due to different land use can be identified. |
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