GDACS Alerts Explained: What Green, Orange and Red Mean
The Global Disaster Alert and Coordination System (GDACS) gives earthquakes, tsunamis, tropical cyclones, floods and volcanic eruptions a color: green, orange or red. The color estimates how likely an event is to need international humanitarian help, from unlikely (green) to likely (red). GDACS is a cooperation framework of the United Nations and the European Commission, and its alerts are estimates for responders, not public warnings.
What is GDACS, and who runs it?
GDACS describes itself as a cooperation framework between the United Nations and the European Commission. Its aim is to fill information and coordination gaps in the first phase after major sudden-onset disasters. The European Commission’s Joint Research Centre (JRC) produces the automatic estimates and risk analysis and chairs the GDACS Advisory Board. The UN Office for the Coordination of Humanitarian Affairs (OCHA) acts as the GDACS Secretariat in Geneva. The GDACS overview page describes the setup.
GDACS is not a national warning agency. In the United States, official warnings come from the National Weather Service, the National Hurricane Center and NOAA’s tsunami warning centers, and earthquake information comes from the USGS. Elsewhere, national meteorological, geological and civil protection agencies play that role.
What do green, orange and red mean in GDACS?
| GDACS color | General meaning in GDACS guidance |
|---|---|
| Green | Unlikely to need international humanitarian assistance, although it can still be a local disaster |
| Orange | A potential local disaster where some international assistance might be needed |
| Red | A potentially severe disaster where international assistance is likely to be needed |
The same physical event can get different colors in different places. GDACS guidelines give an example: an earthquake of the same size in a densely populated area would probably trigger a red alert in a vulnerable country and an orange alert in a developed, resilient country. That is why magnitude or wind speed alone does not set the color.
How does GDACS score earthquakes?
For earthquakes, tsunamis and tropical cyclones, GDACS says all calculations are automatic, without human intervention. Its main earthquake model uses a ShakeMap of estimated shaking, the population within 100 km (62 miles) of the epicenter, a country vulnerability value and the INFORM index of lack of coping capacity.
If no populated place gets shaking above intensity VI on the Modified Mercalli Intensity scale, the alert is green. Otherwise the model weights the number of people exposed to intensities VII, VIII and IX, with the strongest shaking counted most, and turns the result into a score:
- Score below 1: green
- Score from 1 to 2: orange
- Score of 2 or higher: red
GDACS calibrated the score against deaths in past earthquakes. Roughly, scores below 1 correspond to fewer than 10 deaths, 1 to 2 to between 10 and 100, and above 2 to more than 100. When no ShakeMap is available, typically for earthquakes below about magnitude 5.5, GDACS uses a simpler model based on magnitude, depth and exposed population. The method is on the GDACS earthquake model page. For the intensity scale itself, see magnitude vs intensity.
How does GDACS rate tropical cyclones?
GDACS rates cyclones mainly by wind. It sorts storms into Saffir-Simpson categories by 1-minute sustained wind, from tropical storm (34 to 63 knots) to Category 5 (137 knots or more), and compares the category with the number of people exposed and the country’s vulnerability. A Category 3 storm exposing more than 100,000 people, or more than 10 percent of the population, in a country of medium to high vulnerability is red. A Category 3 storm exposing more than 1 million people in a country of low vulnerability is orange.
Storm surge is assessed separately: red at about 10 feet (3 meters) or more, orange at about 3 to 10 feet (1 to 3 meters), green at about 3 feet (1 meter) or less. GDACS says surge is not yet counted in the overall cyclone level. Red levels forecast more than three days ahead are lowered to orange to reduce false alarms. Storm tracks come from the US Joint Typhoon Warning Center and NOAA, as the GDACS cyclone model page explains. Our Saffir-Simpson guide covers the categories.
How are floods and volcanoes rated?
Floods and volcanic eruptions are not fully automatic. GDACS says it currently enters them manually, mainly from information by authoritative institutions, media and scientific organizations.
Floods. GDACS sets the flood level by human impact. Orange means more than 100 dead or 80,000 displaced. Red means more than 1,000 dead or 800,000 displaced. All other floods are green.
Volcanoes. A green alert appears when a Volcanic Ash Advisory Center reports a major rise in ash emission, or when the Smithsonian Institution’s weekly report shows a significant increase in activity. Orange and red are added manually when a significant eruption draws the attention of the humanitarian community. For US volcanoes, the official levels come from the USGS; see volcano alert levels.
The GDACS feed also carries drought and forest fire notifications. On November 9, 2026, most entries in the feed were green forest fire notifications.
Why are GDACS alerts only estimates?
The automatic levels are calculated from early data, such as the first magnitude and location of an earthquake or the forecast track of a storm. When that data is revised, the estimate can change. GDACS’s own disclaimer calls its information “purely indicative” and says it should not be used for decision making without other sources of information. It also says the JRC is not responsible for loss resulting from its use.
A green alert does not mean nobody was hurt. It means the model does not expect a need for international aid, and the GDACS definition of green allows for a local disaster.
How do you read a GDACS alert?
- Read the headline. A GDACS earthquake title gives the color, magnitude, depth, country, time in UTC and the number of people in a shaking band, such as 8 thousand in MMI VI.
- Open the event report for the population figures and score inputs.
- Check the official national source: the USGS event page for earthquakes, the National Hurricane Center for Atlantic and eastern Pacific storms, and the national agencies of the affected country elsewhere.
- For warnings and protective actions, follow national and local authorities, not GDACS.
Our list of current GDACS alerts shows the feed in one place, next to our live list of USGS earthquakes and active storms from the National Hurricane Center.
Bottom line
GDACS colors are automatic or expert estimates of whether a disaster may need international help, produced by the European Commission’s JRC with UN OCHA. Green, orange and red depend on how many people are exposed and how well a country can cope, in addition to magnitude or wind speed. They give a global overview; warnings and instructions come from national agencies and local officials.
FAQ
Is a GDACS red alert an evacuation warning?
No. A red alert estimates that international humanitarian assistance is likely to be needed. Evacuation orders and safety instructions come from national and local authorities.
Why is a strong earthquake sometimes green?
If no populated place gets shaking above intensity VI, GDACS rates the earthquake green. A strong earthquake far offshore or in a sparsely populated area can therefore be green, and a country’s coping capacity also lowers or raises the score.
What hazards does GDACS cover?
GDACS issues notifications for earthquakes, tsunamis, tropical cyclones, floods and volcanoes. Its feed also lists droughts and forest fires.
Can a GDACS alert change after it is issued?
Yes. Alerts follow new data, and GDACS lowers red cyclone levels forecast more than three days ahead to orange to reduce false alarms.