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 seasonal drought indicators in ASIS: Agricultural Stress Index (ASI), Drought Intensity and Mean Vegetation Health Index (Mean VHI). VHI 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, indicate relatively poor vegetation conditions and warmer temperatures, signifying stressed vegetation conditions, and over a longer period would be indicative of drought. In ASIS, VHI is computed in two modality: dekadal and monthly. The dekadal/monthly VHI raster layer published in Hand in Hand Geospatial platform is further updated in the following 5 dekads (improve data precision, remove cloud pixel etc.). Flags of raster file: 251=missing, 252=cloud, 253=snow, 254=sea, 255=background More information, please visit FAO GIEWS Earth Observation website: https://www.fao.org/giews/earthobservation/index.jsp?lang=en Data license policy: Creative Commons Attribution- NonCommercial-ShareAlike 3.0 IGO (CC BY-NC- SA 3.0 IGO) Recommended citation: © FAO - Agricultural Stress Index System (ASIS), http://www.fao.org/giews/earthobservation/, [Date accessed]

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 dekad. The VCI was designed to separate the weather-related component of the NDVI from the ecological element. 𝑉𝐶𝐼𝑖=(𝑁𝐷𝑉𝐼𝑖−𝑁𝐷𝑉𝐼𝑚𝑖𝑛) / (𝑁𝐷𝑉𝐼𝑚𝑎𝑥−𝑁𝐷𝑉𝐼𝑚𝑖𝑛) Together with Temperature Condition Index (TCI), Vegetation Condition Index (VCI) is used to calculate Vegetation Health Index (VHI) using formula: VHI=0.5*VCI+0.5*TCI In ASIS, VCI is computed in two modality: dekadal and monthly. The dekadal/monthly VCI raster layer published in Hand in Hand Geospatial platform is further updated in the following 5 dekads (improve data precision, remove cloud pixel etc.). Flags of raster file: 251=missing, 252=cloud, 253=snow, 254=sea, 255=background More information, please visit FAO GIEWS Earth Observation website: https://www.fao.org/giews/earthobservation/index.jsp?lang=en Recommended citation: © FAO - Agricultural Stress Index System (ASIS), http://www.fao.org/giews/earthobservation/, [Date accessed]

Complementary to Agricultural Stress Index (ASI) which detects the severe and extreme drought, Drought Intensity is another quick-look indicator in ASIS that facilitates the early understanding of the intensity of the drought. It is a new indicator introduced in ASIS 2 (2018). Agricultural droughts are classified by their intensity and are categorized into four classes: Extreme, Severe, Moderate or Mild. The intensity of drought in ASIS is calculated through the weighted Mean Vegetation Health Index, indicating that the poorer the vegetation health the more severe the drought. Drought Intensity dekadal product is processed based on the conditions from the start of the season up to the current dekad. If differs from Drought Intensity Annual product which describes the drought conditions over the entire crop season. Important note: Map legend value= Pixel physical value * multiplier (100), except 251: off season, 252: no data, 253: no season and 254: no crop land, 255: water More information, please visit FAO GIEWS Earth Observation website: https://www.fao.org/giews/earthobservation/index.jsp?lang=en Data license policy: Creative Commons Attribution- NonCommercial-ShareAlike 3.0 IGO (CC BY-NC- SA 3.0 IGO) Recommended citation: © FAO - Agricultural Stress Index System (ASIS), http://www.fao.org/giews/earthobservation/, [Date accessed]

The Weighted Mean Vegetation Health Index (Mean VHI) allows the user to assess the severity of the drought from the start of the growing season, examining the vegetation health and the influence of temperature on plant conditions. It is an average of the dekadal VHI values over the crop growing season (from the start until the last dekad of analysis), weighted by crop coefficients (Kc), assigned to VHI values at the dekads corresponding to the Start of the Season (SOS), Maximum of the Season (MOS) and End of the Season (EOS). Crop coefficient is applied for the purpose of reflecting the crop’s water sensitivity at different phenology stages. Weighted Mean VHI Annual Summary is processed at the end of crop season. It allows the user to assess the overall severity of drought for an entire growing season. Two quick-look indicators in ASIS: Agricultural Stress Index (ASI) and Drought Intensity are both based Mean-VHI dataset. More information please visit FAO GIEWS Earth Observation website: https://www.fao.org/giews/earthobservation/index.jsp?lang=en Data license policy: Creative Commons Attribution- NonCommercial-ShareAlike 3.0 IGO (CC BY-NC- SA 3.0 IGO) Recommended citation: © FAO - Agricultural Stress Index System (ASIS), http://www.fao.org/giews/earthobservation/, [Date accessed]

Complementary to Agricultural Stress Index (ASI) which detects the severe and extreme drought, Drought Intensity is another quick-look indicator in ASIS that facilitates the early understanding of the intensity of the drought. It is a new indicator introduced in ASIS 2 (2018). Agricultural droughts are classified by their intensity and are categorized into four classes: Extreme, Severe, Moderate or Mild. The intensity of drought in ASIS is calculated through the weighted Mean Vegetation Health Index, indicating that the poorer the vegetation health the more severe the drought. The Annual summary of Drought Intensity is processed at the end of crop season. It allows the user to assess the overall intensity of drought for an entire growing season. It differs from Drought Intensity dekadal product, which is based on conditions from the start of the season up to the current dekad. Important note: Map legend value= Pixel physical value * multiplier (100), except 251: off season, 252: no data, 253: no season and 254: no crop land, 255: water More information please visit FAO GIEWS Earth Observation website: https://www.fao.org/giews/earthobservation/index.jsp?lang=en Data license policy: Creative Commons Attribution- NonCommercial-ShareAlike 3.0 IGO (CC BY-NC- SA 3.0 IGO) Recommended citation: © FAO - Agricultural Stress Index System (ASIS), http://www.fao.org/giews/earthobservation/, [Date accessed]

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 dekad. The VCI was designed to separate the weather-related component of the NDVI from the ecological element. 𝑉𝐶𝐼𝑖=(𝑁𝐷𝑉𝐼𝑖−𝑁𝐷𝑉𝐼𝑚𝑖𝑛) / (𝑁𝐷𝑉𝐼𝑚𝑎𝑥−𝑁𝐷𝑉𝐼𝑚𝑖𝑛) Together with Temperature Condition Index (TCI), Vegetation Condition Index (VCI) is used to calculate Vegetation Health Index (VHI) using formula: VHI=0.5*VCI+0.5*TCI In ASIS, VCI is computed in two modality: dekadal and monthly. The dekadal/monthly VCI raster layer published in Hand in Hand Geospatial platform is further updated in the following 5 dekads (improve data precision, remove cloud pixel etc.). Flags of raster file: 251=missing, 252=cloud, 253=snow, 254=sea, 255=background More information, please visit FAO GIEWS Earth Observation website: https://www.fao.org/giews/earthobservation/index.jsp?lang=en Data license policy: Creative Commons Attribution- NonCommercial-ShareAlike 3.0 IGO (CC BY-NC- SA 3.0 IGO) Recommended citation: © FAO - Agricultural Stress Index System (ASIS), http://www.fao.org/giews/earthobservation/, [Date accessed]

Agricultural Stress Index (ASI) - Near Real Time is a quick-look indicator that facilitates the early identification of cropped land with a high likelihood of water stress (drought). It depicts the percentage of arable land, within an administrative area, that has been affected by drought conditions from the start of the season up to the current dekad. It differs from ASI Annual product which describes the drought conditions over the entire crop season. The Index is 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 the pixel level; this calculation includes the use of crop coefficients, which introduces sensitivity of a crop to water stress during each phenological phase. 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). Each administrative area is classified according to the percentage of the affected area to facilitate the quick interpretation of results.

Historic Agricultural Drought Frequency Maps depict the frequency of severe drought in areas where 30 percent/50 percent of the cropland/grassland has been affected. The historical frequency of severe droughts (as defined by ASI) is based on the entire ASI Annual Summary times series (1984-2021). Formula: The number of years when land affected>30 percent/50 percent occurred/(2021-1984+1) *100 Pixel value ranges from 0-100 (unit: percentage). Flag: 252: no data; 253: no season; 254: no cropland/grassland. More information, please visit FAO GIEWS Earth Observation website: https://www.fao.org/giews/earthobservation/index.jsp?lang=en Data license policy: Creative Commons Attribution- NonCommercial-ShareAlike 3.0 IGO (CC BY-NC- SA 3.0 IGO) Recommended citation: © FAO - Agricultural Stress Index System (ASIS), http://www.fao.org/giews/earthobservation/, [Date accessed]

The Weighted Mean Vegetation Health Index (Mean VHI) allows the user to assess the severity of the drought from the start of the growing season, examining the vegetation health and the influence of temperature on plant conditions. The Weighted Mean VHI is an average of the dekadal VHI values over the crop growing season (from the start until the last dekad of analysis), weighted by crop coefficients (Kc), assigned to VHI values at the dekads corresponding to the Start of the Season (SOS), Maximum of the Season (MOS) and End of the Season (EOS). Crop coefficient is applied for the purpose of reflecting the crop’s water sensitivity at different phenology stages. Two quick-look indicators in ASIS: Agricultural Stress Index (ASI) and Drought Intensity are both based Mean-VHI dataset. For more information please visit FAO GIEWS Earth Observation website at: https://www.fao.org/giews/earthobservation/index.jsp?lang=en Data license policy: Creative Commons Attribution- NonCommercial-ShareAlike 3.0 IGO (CC BY-NC- SA 3.0 IGO) Recommended citation: © FAO - Agricultural Stress Index System (ASIS), http://www.fao.org/giews/earthobservation/, [Date accessed]

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 seasonal drought indicators in ASIS: Agricultural Stress Index (ASI), Drought Intensity and Mean Vegetation Health Index (Mean VHI). VHI 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, indicate relatively poor vegetation conditions and warmer temperatures, signifying stressed vegetation conditions, and over a longer period would be indicative of drought. In ASIS, VHI is computed in two modality: dekadal and monthly. The dekadal/monthly VHI raster layer published in Hand in Hand Geospatial platform is further updated in the following 5 dekads (improve data precision, remove cloud pixel etc.). Flags of raster file: 251=missing, 252=cloud, 253=snow, 254=sea, 255=background More information, please visit FAO GIEWS Earth Observation website: https://www.fao.org/giews/earthobservation/index.jsp?lang=en Recommended citation: © FAO - Agricultural Stress Index System (ASIS), http://www.fao.org/giews/earthobservation/, [Date accessed]