The Agricultural Stress Index (ASI) is an index based on the integration of the Vegetation Health Index (VHI) in two dimensions that are critical in the assessment of a drought event in agriculture: temporal and spatial. The first step of the ASI calculation is a temporal averaging of the VHI, assessing the intensity and duration of dry periods occurring during the crop cycle at pixel level. The second step determines the spatial extent of drought events by calculating the percentage of pixels in arable areas with a VHI value below 35 percent (this value was identified as a critical threshold in assessing the extent of drought in previous research by Kogan, 1995). Finally, each administrative area is classified according to its percentage of affected area to facilitate the quick interpretation of results by analysts.

The Agricultural Stress Index (ASI) is an index based on the integration of the Vegetation Health Index (VHI) in two dimensions that are critical in the assessment of a drought event in agriculture: temporal and spatial. The first step of the ASI calculation is a temporal averaging of the VHI, assessing the intensity and duration of dry periods occurring during the crop cycle at pixel level. The second step determines the spatial extent of drought events by calculating the percentage of pixels in arable areas with a VHI value below 35 percent (this value was identified as a critical threshold in assessing the extent of drought in previous research by Kogan, 1995). Finally, each administrative area is classified according to its percentage of affected area to facilitate the quick interpretation of results by analysts.

The mean VHI is an average of the dekadal VHI values over the crop growing season to date. The mean VHI is a good indicator of drought at pixel level. To facilitate analysis, the non-cropland is masked on the mean VHI maps.

The mean VHI is an average of the dekadal VHI values over the crop growing season to date. The mean VHI is a good indicator of drought at pixel level. To facilitate analysis, the non-cropland is masked on the mean VHI maps.

The Annual ASI depicts the percentage of arable land, within an administrative area, that has been affected by drought conditions over the entire cropping season. It differs from the ASI, which is based on conditions from the start of the season up to the current dekad.

The Annual ASI depicts the percentage of arable land, within an administrative area, that has been affected by drought conditions over the entire cropping season. It differs from the ASI, which is based on conditions from the start of the season up to the current dekad.

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.

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.

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.

Precipitation estimates data is obtained from ECMWF.

Precipitation estimates data is obtained from ECMWF.