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Vegetation Drought Response Index (VegDRI)

  
   Vegetation Drought Response Index (VegDRI)
   for the first week of October in 2011.

The Vegetation Drought Response Index (VegDRI) is a weekly geospatial model that depicts drought stress on vegetation within the conterminous United States. The development of the VegDRI drought-monitoring tool was a collaborative effort by scientists at the USGS EROS Center, the National Drought Mitigation Center (NDMC) at the University of Nebraska, and the High Plains Regional Climate Center (HPRCC).

VegDRI methodology integrates remote sensing data from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) sensor on the Terra platform with climate and biophysical data to create a seamless product with a 1 km spatial resolution.

The satellite components related to general vegetation conditions are Percent Annual Seasonal Greenness (PASG) and Start of Season Anomaly (SOSA) data. PASG is calculated weekly from eMODIS Normalized Difference Vegetation Index (NDVI) composites.  

The climate-based drought data include the Palmer Drought Severity Index (PDSI) and weekly Standardized Precipitation Index (SPI) data from the HPRCC. Climate data identify areas that are experiencing dryness to help distinguish vegetation stress due to drought.

The biophysical characteristics of the environment are derived from land use/land cover, soil available water capacity, ecological setting, irrigation status, and elevation data.  Environmental stressors such as land use change, soil conditions, pest infestations, disease, hail, flooding, or fire can also influence vegetation conditions.

This integrated approach considers climate and biophysical conditions to determine the cause of vegetation stress. This information is incorporated into the calculation of VegDRI to create an easy to interpret, color-coded map of drought stress on vegetation.  Drought-monitoring maps are produced every week using the latest information and are usually posted each Monday by 10:30 a.m. CT.

VegDRI Legend

VegDRI Condition VegDRI Values PDSI Values
   Extreme Drought 1 to 64 -7.9375 to -4.0000
   Severe Drought 65 to 80 -3.9375 to -3.0000
     Moderate Drought 81 to 96 -2.9375 to -2.0000
    Pre-Drought 97 to 112 -1.9375 to -1.0000
    Near Normal 113 to 160 -0.9375 to 2.0000
    Unusually Moist 161 to 176 2.0625 to 3.0000
    Very Moist 177 to 192 3.0625 to 4.0000
    Extreme Moist 193 to 252 4.0625 to 7.7500
    Water 253  
    Out of Season 254  
    Other Landcover 255  

VegDRI is a weekly operational product generated within 24 hours of a Terra MODIS overpass time. The eMODIS expedited NDVI composites incorporate estimated ancillary input parameters and provisional near-real-time climate data accessed from the Applied Climate Information System. Due to the rapid production schedule, the input satellite and climate data sets are not subject to extensive quality assurance, and input data errors may influence the accuracy of VegDRI. While the USGS makes every effort to provide accurate and complete information, users should be aware of this potential limitation in VegDRI accuracy.

Digital Products

Weekly VegDRI maps and associated products are available for download through EarthExplorer for the data held in the USGS archive. The download package includes a set of five items contained in a tar file. 

The download package includes

1) VegDRI color map in JPG format.
2) VegDRI product in GeoTIFF format.
3) VegDRI difference product, which is the computed difference between the current and previous week's product, in GeoTIFF format.
4) Percent Average Seasonal Greenness (PASG) product in GeoTIFF format.
5) Metadata for the eMODIS 7-day composite used to generate the VegDRI product.

Data Use and Citation Policies

For information on how to cite USGS data plus guidance on usage restrictions,
please see our Data Citations and Use page at https://lta.cr.usgs.gov/citation.

Contact Information for User Assistance

Long Term Archive User Services
U.S. Geological Survey (USGS)
Earth Resources Observation and Science (EROS) Center
47914 252nd Street
Sioux Falls, SD 57198-0001

Phone Number: 605-594-6151
Toll Free: 800-252-4547
Fax: 605-594-6589

Email:lta@usgs.gov
Web: https://lta.cr.usgs.gov

Business Hours: Monday thru Friday, 8:00 a.m. to 4:00 p.m., Central Time