Mapping vegetation productivity dynamics and degradation trends over East Africa using a decade of medium Resolution MODIS time-series data

摘要

This paper aims to characterize spatial and temporal vegetation productivity trends that could be related to land degradation in East Africa. A decade of AQUA/TERRA-Moderate Resolution Imaging Spectroradiometer (MODIS) satellite observations on vegetation chlorophyll activity, or Normalized Differential Vegetation Index (NDVI) data, and 25-km rainfall data from the TRMM passive radar instrument were used for the same observation period of 2000-2011. Linear trends in land cover based Rain Use Efficiencies (RUE) corrected NDVI and cumulative differences of RUE between consecutive years from 2000 to 2011 (that is amplitudes) were derived and investigated for their robustness. The trend maps were overlaid and classified to map “hot spot” areas of productivity productivity decline. We found vegetation productivity decline areas mostly along the edges of protected areas in Kenya and in the agro-ecological systems in eastern Uganda, whilst the most severely degraded areas were found in southern Ethiopia and eastern Uganda. These severely degraded areas seem to be already under high land use intensities.