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Global Indicators
The vegetation indicators (NDVI anomaly, VCI and VHI) provide alternative measures of the relative vegetation health. These indices can be used to monitor areas where vegetation may be stressed, as a proxy to detect potential drought. The precipitation indicators present a global analysis of the absolute (mm) and relative (%) rainfall levels per dekad, in addition to the long-term average precipitation levels (mm).   More
All three vegetation indicators are based on 10-day (dekadal) vegetation data from the METOP-AVHRR sensor at 1 km resolution (2007 and after). Data at 1 km resolution for the period 1984-2006 was derived from the NOAA-AVHRR dataset at 16 km resolution. Precipitation estimates for all African countries (except Cabo Verde and Mauritius) are taken from NOAA/FEWSNet, while for the remaining countries data is obtained from ECMWF.
YearDekad
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NDVI Anomaly  More
The Normalized Difference Vegetation Index (NDVI) measures the greenness of ground cover, and is used as a proxy to indicate the density and health of vegetation. NDVI values range from +1 to -1, with high positive values corresponding to dense and healthy vegetation, while a low and/or negative NDVI value would indicate poor vegetation conditions or sparse vegetative cover. The NDVI anomaly indicates the variation of the current dekad to the long-term average, where a positive value (for example 20 percent) would signify enhanced vegetation conditions compared to the average, while a negative value (for instance -40 percent) would indicate comparatively poor vegetation conditions.


Vegetation Condition Index  More
The Vegetation Condition Index (VCI) relates the current dekadal NDVI to its long-term minimum, normalized by the historical range of NDVI values for the same dekad. The VCI was designed to separate the weather-related component of the NDVI from the ecological element.


Vegetation Health Index  More
The Vegetation Health Index (VHI) is a composite index and the elementary indicator used to compute the ASI. It combines both the VCI and the Temperature Condition Index (TCI). The TCI is calculated using a similar equation to the VCI, but relates the current temperature to the long-term maximum, as it is assumed that higher temperatures tend to cause a deterioration in vegetation conditions. A decrease in the VHI following, for example, a decline in the VCI (relatively poor green vegetation) and an increasing TCI (warmer temperatures) would signify stressed vegetation conditions, and over a longer period would be indicative of drought. The VHI components (VCI and TCI) are given equal weights when computing the index. The VHI images are computed for the two main seasons and in three modalities: dekadal, monthly and annual.


YearDekad
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Estimated Precipitation  More
Precipitation estimates data is obtained from ECMWF.


Precipitation Anomaly


Estimated Precipitation (long term average)


YearMonth
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NDVI Anomaly  More
The Normalized Difference Vegetation Index (NDVI) measures the greenness of ground cover, and is used as a proxy to indicate the density and health of vegetation. NDVI values range from +1 to -1, with high positive values corresponding to dense and healthy vegetation, while a low and/or negative NDVI value would indicate poor vegetation conditions or sparse vegetative cover. The NDVI anomaly indicates the variation of the current dekad to the long-term average, where a positive value (for example 20 percent) would signify enhanced vegetation conditions compared to the average, while a negative value (for instance -40 percent) would indicate comparatively poor vegetation conditions.


Vegetation Condition Index  More
The Vegetation Condition Index (VCI) relates the current dekadal NDVI to its long-term minimum, normalized by the historical range of NDVI values for the same dekad. The VCI was designed to separate the weather-related component of the NDVI from the ecological element.


Vegetation Health Index  More
The Vegetation Health Index (VHI) is a composite index and the elementary indicator used to compute the ASI. It combines both the VCI and the Temperature Condition Index (TCI). The TCI is calculated using a similar equation to the VCI, but relates the current temperature to the long-term maximum, as it is assumed that higher temperatures tend to cause a deterioration in vegetation conditions. A decrease in the VHI following, for example, a decline in the VCI (relatively poor green vegetation) and an increasing TCI (warmer temperatures) would signify stressed vegetation conditions, and over a longer period would be indicative of drought. The VHI components (VCI and TCI) are given equal weights when computing the index. The VHI images are computed for the two main seasons and in three modalities: dekadal, monthly and annual.


YearMonth
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Estimated Precipitation  More
Precipitation estimates data is obtained from ECMWF.


Precipitation Anomaly


Estimated Precipitation (long term average)



Start of Season


End of Season



Start of Season


End of Season