Events are identified daily or upon request, when a relevant forest fire is having impacts that could interest the humanitarian community. Not all wildfire events generated by GWIS enter the GDACS platform. A first filter allows only the fire events that have a burnt area of at least 5000 hectares. When a smaller wildfire could potentially cause humanitarian impacts (e.g. contiguous to urban areas), this event is manually inserted into the GDACS system upon expert judgement. A second filter is applied to the events visible on GDACS homepage, where only wildfires with burned area exceeding 10000 ha and population within 5 km exceeding 10000 are shown. The fires information and the map are updated every day, provided enough data are made available to GWIS from imagery providers.
Burnt area information is generated by GWIS, specifically its Near-Real Time (NRT) product, based on the use of thermal anomalies from MODIS and VIIRS sensors (more below). The indicator defines individual wildfire perimeters, therefore estimates the burnt area caused by the fires. GWIS uses the active fire detection provided by the NASA FIRMS (Fire Information for Resource Management System).
MODIS Active fires
The MODIS sensor, on board of the TERRA and ACQUA satellites, identifies areas on the ground that are distinctly hotter than their surroundings and flags them as active fires (more info). The difference in temperature between the areas that are actively burning with respect to neighbouring areas allows active fires to be identified and mapped. The spatial resolution of the active fire detection pixel from MODIS is 1 km.
VIIRS Active fires
The VIIRS (Visible Infrared Imaging Radiometer Suite) on board the NASA/NOAA Suomi National Polar-orbiting Partnership (SNPP) uses similar algorithms to those used by MODIS to detect active fires. The VIIRS active fire products complement the MODIS active fire detection and provide an improved spatial resolution, as compared to MODIS. The spatial resolution of the active fire detection pixel for VIIRS is 375 m. Additionally, VIIRS is able to detect smaller fires and can help delineate perimeters of ongoing large fire.
GDACS Alert Score:
The GDACS alert level is defined in a semi-automatic way, based on the expert assessment of the impacts of the wildfire.
| GDACS Alert Level |
Description |
| Red |
This is assigned to a wildfire of any size that has severe impacts to people and assets, with hundreds or thousands of displaced people and often tens of fatalities. Moreover, the red class is assigned in case of UCPM activations for sizeable fires and a low coping capacity of the country or area affected. |
| Orange |
This level refers to wildfires of any size that impact directly the people and built-up areas, possibly resulting in some fatalities. Orange is attributed in case of UCPM activations too, with the exceptions of countries where usually UCPM is not adopted (e.g. the USA). |
| Green |
For events of at least 5000 hectares (50 square km) provided by GWIS, the green alert level is attributed automatically, even in absence of impacts. Smaller wildfires may enter GDACS as green events in case of minor impacts to people or assets, or when preparedness measures were implemented or planned in response to the wildfire (e.g. evacuation orders for threatened buildings). Notice that GDACS homepage will display “green” wildfires only if burned area exceeds 10000 ha and population within 5 km exceeding 10000. Smaller ones will be available from the search page only. |
For wildfires, at present, the numerical score can only get one of three values, corresponding to the respective class: 0.5 for green events, 1.5 for orange events and 2.5 for red events.
