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]

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.

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 Agricultural Stress Index (ASI) is a quick-look indicator that facilitates the early identification of cropped land with a high likelihood of water stress (drought). ASI related products (maps, spatial aggregation based on administrative unit) are processed by FAO GIEWS (Global Information and Early Warning System on Food and Agriculture) every 10 days. ASI Annual Summary is processed at the end of crop season. It 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 ASI dekadal product, which is based on conditions from the start of the season up to the current dekad. 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. 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 System (ASIS) is a global agricultural drought monitoring system developed and operated by FAO which enables to monitor agricultural areas affected by dry spells, or severe drought in extreme cases, using satellite data. It provides a collective quick-look indicators that facilitate the early identification of cropland/grassland with a high likelihood of water stress (drought). ASIS related products (maps, zonal statistics) are processed by FAO GIEWS (Global Information and Early Warning System on Food and Agriculture) every 10 days. Pre-processed, published-ready maps, zonal statistics of ASIS are published FAO GIEWS Earth Observation website at: https://www.fao.org/giews/earthobservation/index.jsp?lang=en. All ASIS raster datasets are accessible through the FAO Hand-in-Hand Geospatial Portal, Web Map Service (WMS) and Google Earth Engine (GEE). More information, please visit ASIS Data Access page: https://www.fao.org/giews/earthobservation/access.jsp?lang=en Agricultural Stress Index System is composed of two type of indicators: seasonal indicators such as Agricultural Stress Index (ASI) to detect the severe agricultural drought, Drought Intensity to classify the severity of the drought and no-seasonal indicators, such as vegetation indicators (NDVI anomaly, VCI and VHI). The seasonal indicators are designed to allow easy identification of areas of cropped land with a high likelihood of water stress (drought). The indices are based on remote sensing data of vegetation and land surface temperature combined with information on agricultural cropping cycles derived from historical data and a global crop mask. The final maps highlight anomalous vegetation growth and potential drought in crop zones during the growing season. In ASIS, two cropping cycles (major season /minor season) and crop/grassland zones are applied. Some countries have three or four crop seasons within a crop year. For these countries, Global ASIS cannot properly capture the agricultural drought occurred between the first and the last season (e.g. for a country has four crop seasons, the drought occurred during the 2nd and 3rd season). The satellite data used in the calculation of the mean VHI and the ASI is the 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. The crop/grass mask is FAO GLC-SHARE. Pixel with at least 5% covered by the class is defined as a cropland/grassland pixel. 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] For more information, please visit GIEWS Earth Observation website.