Satellites can detect the difference between rock, grassland, and forests because these surfaces emit energy differently back into space. By measuring these differences and observing the patterns of vegetation --or its lack of growth--NOAA scientists can monitor how droughts are changing across the world through time.
This global drought risk composite is derived from datasets developed by NOAA from measurements on the Visible-Infrared Imager/Radiometer Suite, or VIIRS, onboard the NPP satellite. By monitoring vegetation health, moisture and thermal conditions, scientists are able to identify areas that are considered to be vegetatively stressed due to drought. An important note is that the drought imagery is based solely on the analysis of vegetation health and stress, not soil moisture conditions. But this index serves as a reliable proxy measurement for drought worldwide. Areas of desert and snow cover are not included in the analysis. Yellow areas indicate areas under moderate drought conditions; red indicates areas experiencing extreme drought conditions. Other VIIRS datasets include Nighttime Lights, Vegetation Real-time, Fires - Real-time and Earth in True Color (daily) - Real-time.