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 creation: 2014-01-01
Supplemental Information:
No data value: -9999
Citation:
Recommended citation: @ FAO - Agricultural Stress Index System (ASIS), http://www.fao.org/giews/earthobservation/, [Date accessed]
Contact points:
Resource Contact: Yanyun Li
Metadata Contact: Global Information and Early Warning System (GIEWS)
Resource constraints:
Data license policy: Creative Commons Attribution- NonCommercial-ShareAlike 3.0 IGO (CC BY-NC- SA 3.0 IGO)
Online resources:
Global Vegetation Health Index monthly map
