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| Titel |
Analysis of vegetation and land cover dynamics in north-western Morocco during the last decade using MODIS NDVI time series data |
| VerfasserIn |
C. Höpfner, D. Scherer |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 8, no. 11 ; Nr. 8, no. 11 (2011-11-17), S.3359-3373 |
| Datensatznummer |
250006205
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| Publikation (Nr.) |
 copernicus.org/bg-8-3359-2011.pdf |
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| Zusammenfassung |
Vegetation phenology as well as the current variability and dynamics of
vegetation and land cover, including its climatic and human drivers, are
examined in a region in north-western Morocco that is nearly 22 700 km2
big. A gapless time series of Normalized Differenced Vegetation Index (NDVI)
composite raster data from 29 September 2000 to 29 September 2009 is
utilised. The data have a spatial resolution of 250 m and were acquired by
the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor.
The presented approach allows to compose and to analyse yearly land cover
maps in a widely unknown region with scarce validated ground truth data by
deriving phenological parameters. Results show that the high temporal
resolution of 16 d is sufficient for (a) determining local land cover better
than global land cover classifications of Plant Functional Types (PFT) and
Global Land Cover 2000 (GLC2000) and (b) for drawing conclusions on
vegetation dynamics and its drivers. Areas of stably classified land cover
types (i.e. areas that did not change their land cover type) show
climatically driven inter- and intra-annual variability with indicated
influence of droughts. The presented approach to determine human-driven
influence on vegetation dynamics caused by agriculture results in a more
than ten times larger area compared with stably classified areas. Change
detection based on yearly land cover maps shows a gain of high-productive
vegetation (cropland) of about 259.3 km2. Statistically significant
inter-annual trends in vegetation dynamics during the last decade could
however not be discovered. A sequence of correlations was respectively
carried out to extract the most important periods of rainfall responsible
for the production of green biomass and for the extent of land cover types.
Results show that mean daily precipitation from 1 October to 15 December has
high correlation results (max. r2=0.85) on an intra-annual time scale to NDVI
percentiles (50 %) of land cover types. Correlation results of mean daily
precipitation from 16 September to 15 January and percentage of yearly
classified area of each land cover type are medium up to high (max. r2=0.64).
In all, an offset of nearly 1.5 months is detected between
precipitation rates and NDVI values. High-productive vegetation (cropland)
is proved to be mainly rain-fed. We conclude that identification,
understanding and knowledge about vegetation phenology, and current
variability of vegetation and land cover, as well as prediction methods of
land cover change, can be improved using multi-year MODIS NDVI time series
data. This study enhances the comprehension of current land surface dynamics
and variability of vegetation and land cover in north-western Morocco. It
especially offers a quick access when estimating the extent of agricultural
lands. |
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