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| Titel |
Quantifying lavaka (gully) density and extension using freely accessible satellite imagery |
| VerfasserIn |
Andrea Raveloson, Brigitta Ludván, Balázs Székely |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250086821
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| Publikation (Nr.) |
 EGU/EGU2014-754.pdf |
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| Zusammenfassung |
| Land Degradation in Madagascar is a complex challenge due to spectacular gullies (called
lavaka) that have a number of undesirable effects. Lavaka have been observed for a long time.
Nevertheless their real nature and contribution to total soil loss is still unclear. This is
probably due to the fact that they occur in great number and size in the Highlands of
Madagascar, therefore their quantification and study is very hard making field surveys time
consuming.
The aim of this study was to quantify the lavaka density at various parts of the Highlands
of Madagascar using satellite imagery. To this end 10 test areas of size of 250-300 km2 has
been selected. In these areas we were able to identify, classify and map the approximate
extent (length and width) of the gullies from Google Earth images. Gully location and
characteristics (type and size) were integrated in a conventional GIS. Gully abundance maps
were created for each study area by inspecting the available imagery at 1 km x 1 km grid
cells. These maps were then examined against several raster and vector data layer
representing various landscape variables such a slope angle, elevation and relief
(derived from SRTM) as well as geology, soil precipitation and the possible human
influence.
Visualization of imagery showed that lavaka density in the studied areas varies greatly,
even locally from one cell to another. The average lavaka density is 2.2 lavaka per km2 with a
maximum of 30 lavaka per km2. Lavaka size also shows great diversity, reaching up to 1000
m in length and few100m in width.
Results show a strong relationship between gully presence, tree cover, elevation, relief
and slope angle. Geology, soil and precipitation seem to be less important in a medium scales
notwithstanding with the fact that many studies dealing with lavaka emphasize their
importance in lavakization process. Most of the lavaka seem to be a natural part of the
landscape and this assumption was supported by lavaka-like features interpreted as
paleolavaka found while inspecting imagery.
Further studies will concentrate on the role of the spatial and temporal distribution of
precipitation.
This is ILARG-contribution Nr. 10. |
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