Vegetation Drought Response Index (VegDRI)

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 NASAs 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.