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Normalized Difference Vegetation Index(NDVI) in Southwest Asia on
   
 
    

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NDVI
 
Normalized Difference Vegetation Index (NDVI) is calculated as

where and are the reflectance in the near infrared (NIR) and red bands respectively. NDVI reflects vegetation vigor, density and biomass and is effectively determined by both – landscape and meteorology. The NDVI is the most commonly used vegetation index. It varies in a range of -1 to + 1.

 
 
NDVI Deviation from the mean
 


NDVI itself does not reflect drought or non-drought conditions. But the severity of a drought (or the extent of wetness – on the other end of the spectrum) may be defined as NDVI deviation from its long-term mean (DEVNDVI). This deviation is calculated as the difference between the NDVI for the current time step (e.g., January 1995) and a long-term mean NDVI for that month (e.g., a 20-year long mean NDVI of all Januaries from 1982 to 2001) for each pixel:

where NDVIi is the NDVI value for month i and NDVImean,m is the long-term mean NDVI for the same month m, (there are twelve long-term NDVI means for each pixel: one mean for each calendar month). When DEVNDVI is negative, it indicates the below-normal vegetation condition/health and therefore suggests a prevailing drought situation. The greater the negative departure, the greater is the magnitude of a drought.

 
 
Vegetation Condition Index (VCI).
 

VCI was designed to single out the impact of meteorological conditions on vegetation. It shows how close the NDVI of the current month is to the minimum NDVI calculated from the long-term record.

where NDVImaxand NDVIminare calculated from the long-term record for that month (or week) and j is the index of the current month (week). The condition/health of the ground vegetation presented by VCI is measured in percent. VCI values around 50% reflect fair vegetation conditions. The VCI values between 50 to 100 % indicate optimal or above-normal conditions. At the VCI value of 100% the NDVI value for this month (or week) is equal to NDVImax. Different degrees of a drought severity are indicated by VCI values below 50%. Kogan (1995) illustrated that the VCI threshold of 35% may be used to identify extreme drought conditions. The VCI value close to zero % reflects an extremely dry month, when NDVI value is close to its long-term minimum. Low VCI values over several consecutive time intervals point to drought development.

 
 
 
 
 
 
 
Hold the mouse over the map. District with data will show their names. To go to a district/province view of vegetation indices, click on an "active" district of your choice.
 
 
Other indices for    
Indices for past dates:    
 
 
 
 
     
 
 
 
(c) International Water Management Institute (IWMI)