The Global Disaster Alert and Coordination System provides near real-time alerts about natural disasters around the world and tools to facilitate response coordination, including media monitoring, map catalogues and Virtual On-Site Operations Coordination Centre.

Asgard alert levels

Asgard combines information on the event, the population in the affected area and the vulnerability of that population to derive an alert level that indicates the probability for a catastrophic situation with needs for international humanitarian intervention. The way these three types of information are combined varies with the disaster type.

Earthquakes

Currently, the evaluation of the potential humanitarian impact of earthquakes considers (1) earthquake magnitude (in units reported by source), (2) earthquake depth, (3) population within 100km of epicentre, and (4) national population vulnerability. Elements 1 and 2 are scraped from seismological sources, while elements 3 and 4 are automatically calculated by a GIS based on epicentre location (latitude and longitude), the Landscan population dataset and ECHO's Global Needs Assessment indicator.

The formula for the threshold is calculated as follows. This formula was established based on statistical analysis and minimization of omission and commission errors of historical earthquake disasters.

First, the alert score is calculated:

• P = sqrt (log₁₀ ( Max (Pop100 / 80000, 1)))
  If Pop100 > 80000 (the cut off population threshold), then P is the square root of the 10 logarithm of Pop100/80000.
  This means that we assume an exponential relationship between impact and population, with a cut off of 80000 people within an area of 31415,6 km², or a population density of about 2,5 people per km².
   
• M = Max ( magnitude - 4.5, 0 )
  If the magnitude is above 4.5, then M is the magnitude - 4.5.
  This means that we do not consider earthquakes of a magnitude lower than 4.5. Further, we assume - for strong earthquakes - a linear relationship between impact and magnitude.
   
• V = GNA Index for closest country (a value between 0 and 3)
  If GNA is missing, then V defaults to 0.5.
  The GNA is a combination of 9 socio-economic and historical indicators that are computed based on ranking and classification. The value (between 0 and 3) is not a quantitative value, but qualitative value.

These factors are combined and weighted as follows:

draft_alert_score = (P * M * V^1.5) / 3

This formula gives a higher weight to the vulnerability of the country, therefore emphasizing that prepared and rich countries with good building standards that can be enforced can better cope with earthquakes than other countries. Equivalent earthquakes are more likely to be a disaster in vulnerable countries.

Subsequently, the draft alert score is modified according to the following rules:

• If the magnitude is less than 6, no red alerts can be issued. In other words, if the draft_alert_score is larger than 2, it is set to 2.
• If the earthquake occurred more than 100km deep, the draft_alert_score is reduced by 1.
• If the earthquake occurred deeper than 300km, the draft_alert_score is set to 0, or a green alert.

Finally, the alert score is transformed into an alert level according to the following thresholds:

• Red: more than 2
• Orange: between 1 and 2
• Green: less than or equal to 1

At the same time, the tsunami alert score is calculated (see below).

Tsunamis (Updated 2009)

GDACS tsunami alert calculations are triggered by earthquakes that occur in or near¹ water. The logic for the tsunami alert is based on (1) the magnitude of the earthquake, (2) the depth of the earthquake, (3) the maximum wave height at any coast reach by the tsunami. The first two parameters are used to look up a tsunami wave height calculation in the JRC Tsunami Database (containing over 132000 scenarios).

For each earthquake of magnitude exceeding 6.5 occuring in a location with positive water depth (from ETOPO30), the tsunami database is queried for the closest matching scenario. Scenarios have been calculated for 13800 locations covering tsunamogenic areas (from NOAA database) for magnitudes ranging from 6.5M to 9.5M with steps of 0.25M.

If a scenario is available, the maximum wave height at a coast is retrieved. If the maximum wave height is greater or equal than 3m, the tsunam alert is Red; if it the height is greater or equal than 1m, the alert is Orange; otherwise, the alert is Green. These values are then corrected for earthquake depth in the same way as for earthquakes².

If no scenario has been precalculated (only very few cases), a new calculation is started (taking about 20 minutes), but the alert routine does not take it into account. Rather, the IOC alert Matrix is used (see figure below), based only on magnitude. This fall-back routine, although widely used in tsunami warning centres, results in many false alerts.

¹ In 2009, we will extend this to zones near the coast (5km) to account for rupture zones that are partially on land and partially in sea.

² JRC is working on a better depth correction algorithm, taking into account attenuation using the Okada model.

Volcanoes

GDACS no longer provides volcano alerts. Rather, it posts information from the Global Volcanism Program (Smithsonian Institute) and the USGS Volcano Service.

Previously, volcano alerts were taken from the source (South West Volcano Research Centre), with the exception that the population near the volcano is taken into consideration. Note that these alerts are not published anymore on the homepage, nor are they included in the GDACS newsletter. In consultation with the Global Volcanism Program, WOVO and USGS, the methodology is being revised.

Tropical cyclones

Based on track information provided by the Pacific Disaster Center, JRC calculates areas around the track affected by high winds. In these areas, GDACS calculates population and critical infrastructure. Depending on the wind speed and the population in the area, alert levels are set as follows:

• Population < 100000: Green alert
• Population > 100000 in Cat1: Orange alert
• Population > 100000 in Cat1, with maximum wind speeds of Cat3 or up: Red alert

In addition, GDACS calculates population potentially affected by storm surge, but this is not taken into account in the alert model. One important aspect that does influence the alert model is extreme rainfall, but no suitable models have been found and integrated as of now.

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