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| Titel |
Inter-annual and seasonal trends of vegetation condition in the Upper Blue Nile (Abay) Basin: dual-scale time series analysis |
| VerfasserIn |
E. Teferi, S. Uhlenbrook, W. Bewket |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
2190-4979
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| Digitales Dokument |
URL |
| Erschienen |
In: Earth System Dynamics ; 6, no. 2 ; Nr. 6, no. 2 (2015-09-25), S.617-636 |
| Datensatznummer |
250115480
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| Publikation (Nr.) |
 copernicus.org/esd-6-617-2015.pdf |
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| Zusammenfassung |
| A long-term decline in ecosystem functioning and productivity, often called
land degradation, is a serious environmental challenge to Ethiopia that
needs to be understood so as to develop sustainable land use strategies.
This study examines inter-annual and seasonal trends of vegetation cover in
the Upper Blue Nile (UBN) or Abbay Basin. The Advanced Very High Resolution
Radiometer (AVHRR)-based Global Inventory, Monitoring, and Modeling
Studies (GIMMS) normalized difference vegetation index (NDVI) was used for
long-term vegetation trend analysis at low spatial resolution.
Moderate Resolution Imaging Spectroradiometer (MODIS) NDVI data (MOD13Q1)
were used for medium-scale vegetation trend analysis. Harmonic analyses and
non-parametric trend tests were applied to both GIMMS NDVI (1981–2006) and
MODIS NDVI (2001–2011) data sets. Based on a robust trend estimator
(Theil–Sen slope), most parts of the UBN (~ 77 %) showed a
positive trend in monthly GIMMS NDVI, with a mean rate of 0.0015 NDVI units
(3.77 % yr−1), out of which 41.15 % of the basin depicted
significant increases (p < 0.05), with a mean rate of 0.0023 NDVI
units (5.59 % yr−1) during the period. However, the MODIS-based
vegetation trend analysis revealed that about 36 % of the UBN showed a
significant decreasing trend (p < 0.05) over the period 2001–2011 at
an average rate of 0.0768 NDVI yr−1. This indicates that the greening
trend of the vegetation condition was followed by decreasing trend since the
mid-2000s in the basin, which requires the attention of land users and
decision makers. Seasonal trend analysis was found to be very useful to
identify changes in vegetation condition that could be masked if only
inter-annual vegetation trend analysis was performed. Over half (60 %) of
the Abay Basin was found to exhibit significant trends in seasonality over
the 25-year period (1982–2006). About 17 and 16 % of the significant
trends consisted of areas experiencing a uniform increase in NDVI throughout
the year and extended growing season, respectively. These areas were found
primarily in shrubland and woodland regions. The study demonstrated that
integrated analysis of inter-annual and intra-annual trends based on GIMMS
and MODIS enables a more robust identification of changes in vegetation condition. |
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