Non-Seasonal Indicators

ASIS non seasonal indictors include: NDVI anomaly, Vegetation Condition Index (VCI) and Vegetation Health Index (VHI). These indices can be used to monitor the areas where vegetation may be stressed, as a proxy to detect potential drought. They are computed in two modality: dekadal and monthly.

The Vegetation Condition Index (VCI) evaluates the current vegetation health in comparison to the historical trends. The VCI relates current dekadal Normalized Difference Vegetation Index (NDVI) to its long-term minimum and maximum, normalized by the historical range of NDVI values for the same period. The VCI was designed to separate the weather-related component of the NDVI from the ecological element.

The Vegetation Health Index (VHI) illustrates the severity of drought based on the vegetation health and the influence of temperature on plant conditions. The VHI is a composite index and the elementary indicator used to compute the ASI. It combines both the Vegetation Condition Index (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 and minimum, as it is assumed that higher temperatures tend to cause a deterioration in vegetation conditions. A decrease in the VHI would, for example, indicates relatively poor vegetation conditions and warmer temperatures, signifying stressed vegetation conditions, and over a longer period would be indicative of drought.

More information can be found here

Data and Resources

Additional Info

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Maintainer Global Information and Early Warning System
Maintainer email giews1@fao.org
Last Updated April 26, 2023, 06:55 (UTC)
Created May 20, 2022, 07:53 (UTC)