GDACS Alert Colours Explained: Why a Huge Earthquake Can Be Rated Green

Direct answer: GDACS — the Global Disaster Alert and Coordination System, run jointly by the United Nations and the European Commission — gives each major event a colour that estimates humanitarian impact, not hazard size. Green means international assistance is unlikely to be needed. Orange means local or regional impact is possible. Red means severe impact is likely and an international response is probable.

What GDACS is for

GDACS exists to answer one question for disaster responders in the first hour: do we need to mobilise? It is a coordination tool for governments, UN agencies and NGOs, not a scientific measure of the hazard. USGS tells you the earthquake was M7.1. GDACS tries to tell you whether that M7.1 is going to need field hospitals.

The system runs automatically. Within roughly half an hour of a qualifying event, GDACS pulls the hazard parameters from the primary scientific source, models the affected footprint, and overlays population and vulnerability data to produce a score and a colour.

The three ingredients of a GDACS score

• Hazard magnitude — earthquake magnitude and depth, cyclone wind speed and track, flood extent, volcanic activity level.
• Exposure — how many people live inside the modelled impact footprint, from gridded population datasets.
• Vulnerability and coping capacity — a country-level index reflecting building stock, income, governance and previous disaster response performance. The same shaking produces very different casualty counts in Japan and in a country with widespread unreinforced masonry.

Why a big earthquake can be Green

This is the single most misread part of the system. An M7.0 in an uninhabited desert, in the middle of an ocean, or 500 km deep beneath a sparsely populated region will often be Green — because nobody is exposed. Meanwhile an M6.2 at 10 km depth under a dense city with fragile housing can go straight to Red.

Green does not mean "nothing happened" or "nobody was hurt". It means GDACS does not expect the event to overwhelm national capacity. People can still die in a Green event.

Alert colours by hazard type

• Earthquakes — scored from magnitude, depth and modelled shaking against population and vulnerability.
• Tropical cyclones — scored from forecast wind speed and track, with population inside each wind band. The score updates as the forecast track shifts, so a cyclone can escalate from Green to Red over successive advisories.
• Floods — modelled from rainfall, river discharge and satellite-observed extent; these usually update over days, not minutes.
• Volcanoes, droughts and wildfires — scored from activity indices and affected area, with lower resolution than the earthquake and cyclone models.

What GDACS is not good at

It is an automatic model, and it says so itself. Known limitations worth keeping in mind:

• Speed over accuracy. The first score uses the first magnitude estimate. If the magnitude is revised, the colour can change.
• Secondary hazards are hard. Landslides, dam failures, fires after earthquakes and disease outbreaks after floods are largely outside the model.
• Slow-onset disasters fit badly. Drought and food insecurity build over months and are not well captured by an alert designed for sudden events.
• Cross-border and long-duration flooding is frequently under-scored early on.

The 2023 Türkiye-Syria earthquake is a fair illustration of the system working as designed: it was placed at the top of the scale very quickly, and international teams were moving on the strength of that signal long before verified casualty figures existed.

How this site uses GDACS

We map GDACS colours onto our own severity levels — Green to moderate, Orange to severe, Red to extreme — and we never use colour alone: every severity label on the site is written out in text with a bar indicator beside it, so it is readable if you cannot distinguish the colours. Each GDACS-sourced event page links back to the original GDACS bulletin so you can read the underlying model output.

See the full list of feeds we aggregate on the data sources page, and the current global picture on the live map.

Frequently asked questions

Who runs GDACS?

GDACS is a cooperation framework between the United Nations and the European Commission Joint Research Centre, with the aim of coordinating international disaster response in the first hours after a major event.

Does a Green GDACS alert mean nobody was hurt?

No. Green means GDACS does not expect the event to require international assistance. People can still be killed or injured in a Green event — it is a judgement about response capacity, not about harm.

Why is a magnitude 7 earthquake sometimes Green and a magnitude 6 sometimes Red?

Because the score combines hazard size with how many people are exposed and how vulnerable they are. A large earthquake in an empty region scores low; a moderate, shallow earthquake under a dense city with fragile housing scores high.

How quickly does GDACS issue an alert?

Typically within about half an hour of a qualifying event, using the first available scientific parameters. The colour can change as those parameters are revised.

Can I subscribe to GDACS alerts directly?

Yes — GDACS offers free email and SMS alert subscriptions on gdacs.org. This site also republishes GDACS-sourced events with a link to the original bulletin.

Sources

• GDACS — About
• European Commission Disaster Risk Management Knowledge Centre
• UN OCHA — Global Disaster Alert and Coordination System
• INFORM Risk Index (vulnerability and coping capacity data)

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