Disaster Scales

Disaster Scales#

Reference of the standard intensity / magnitude scales used in weather, geophysical, and human-caused disaster reporting. Operators meet these in incident summaries, BCP / DR planning, and OSINT around natural events.

For incident-response coordination, see Law Enforcement and Security.

Tropical cyclones (Saffir-Simpson)#

Category	Sustained wind / damage
Tropical Depression	≤ 38 mph (61 km/h); ≤ 33 kt.
Tropical Storm	39-73 mph (62-117 km/h); 34-63 kt.
Cat 1	74-95 mph (119-153 km/h); minimal damage.
Cat 2	96-110 mph (154-177); moderate.
Cat 3	111-129 mph (178-208); major; first “major hurricane”.
Cat 4	130-156 mph (209-251); severe.
Cat 5	≥ 157 mph (252+); catastrophic.

Other basins use different naming:

Region	Term + scale
Atlantic / E. Pacif ic	Hurricane (Saffir-Simpson Cat 1-5).
Pacific	Typhoon; Severe / Very Strong / Violent typhoon (JMA + Hong Kong scales differ).
Pacific / S. Ind	ian Tropical / Severe Tropical Cyclone (Australian Cat 1-5).
Indian	Cyclone (IMD: Cyclonic Storm to Super Cyclonic Storm).
Bay of Bengal / Arabian Sea	similar IMD scale.

Tornadoes (Enhanced Fujita)#

EF rating	3-second wind gust
EF0	65-85 mph (105-137 km/h); minor.
EF1	86-110 mph; moderate; mobile homes overturned.
EF2	111-135 mph; significant; roofs torn off.
EF3	136-165 mph; severe; well-built homes destroyed.
EF4	166-200 mph; devastating.
EF5	≥ 201 mph; incredible.

The original Fujita (F0-F5) scale was retired 2007; EU uses the TORRO scale (T0-T11). Doppler-radar profile estimates when no damage is observable; otherwise damage assessment is the post-event metric.

Earthquakes#

Scale	Notes
Moment magnitude	Mw; the standard since 1990s; logarithmic energy.
(Mw)	Each step = ~32x energy.
Richter (ML)	local-magnitude; obsolete >= 6.5; valid for small / nearby quakes.
Surface-wave (Ms)	long-period; saturates around 8.
Body-wave (mb)	short-period.
Modified Mercalli	I (not felt) … XII (total destruction); a intensity
	scale based on observed effects, not energy.
JMA scale (Japan)	0-7; intensity-based.
PGA / PGV	peak ground acceleration / velocity (engineering).

Felt-effect anchor (MMI):

MMI	Effect
I	not felt.
II-III	felt by sensitive observers / those at rest.
IV-V	generally felt; light damage.
VI-VII	felt by all; moderate damage.
VIII-IX	considerable damage to ordinary structures.
X-XII	most masonry / frame structures destroyed.

Volcanoes (VEI)#

Volcanic Explosivity Index (Newhall & Self 1982):

VEI	Notes
0	non-explosive (Hawaiian effusive).
1	gentle (Stromboli regular activity).
2	explosive (Galeras 1992).
3	severe (Nevado del Ruiz 1985).
4	cataclysmic (Eyjafjallajökull 2010, Mount Pelée 1902).
5	paroxysmal (St. Helens 1980, Vesuvius 79 CE).
6	colossal (Krakatoa 1883, Pinatubo 1991, Hunga Tonga 2022).
7	mega-colossal (Tambora 1815, Mazama).
8	apocalyptic (Yellowstone 640k years ago, Toba ~74k).

VEI is logarithmic in ejecta volume; each step ~10x. There are no historical VEI-8 events; VEI-7 has happened ~5 times in human history.

Tsunamis (Soloviev / Imamura-Iida)#

Scale	Notes
Imamura-Iida (m)	H-rating from -1 (no observable) … 4 (catastrophic regional impact).
Soloviev intensity	more granular; -1 … 5.
2-2004 (Sumatra)	H ~4; >227,000 dead.
2011 Tōhoku	H ~3-4; ~20,000 dead; Fukushima Daiichi disaster.

Wind (Beaufort)#

Force	Description (mean wind speed)
0	Calm < 1 mph.
1	Light air 1-3 mph.
2	Light breeze 4-7 mph.
3	Gentle 8-12.
4	Moderate 13-18.
5	Fresh 19-24.
6	Strong 25-31.
7	Near gale 32-38.
8	Gale 39-46.
9	Strong gale 47-54.
10	Storm 55-63.
11	Violent storm 64-72.
12	Hurricane force ≥ 73.

Originally for sailing; modern marine + WMO definitions extended Force 12 with Force 13-17 in some uses.

Wildfire#

Scale / type	Notes
Burning Index (US)	daily fire-danger composite (NFDRS).
Spread Component	rate of spread component.
NFDRS Adjective	Low / Moderate / High / Very High / Extreme.
FDI (AU)	Forest Fire Danger Index; >100 = catastrophic.
Canadian FWI	Fire Weather Index.
EFFIS (EU)	European Forest Fire Information System ratings.
Fire size class	A (<0.25 acre) … G (5000+ acres), US.
Type 1 / 2 / 3 / 4	/ 5 US incident-management complexity, 1 = most complex.

Floods#

Concept	Notes
Stage / gauge	water height at gauging station.
Discharge	flow volume (cumecs / cfs).
1-in-100-year	annual exceedance probability 1%; not “once per century”.
Action / Minor / Moderate / Major	NWS gauge categories; specific to each gauge.
500-year flood	0.2% AEP.

Avalanches / snow#

Scale	Notes
Avalanche Danger	1 (Low) … 5 (Extreme); EAWS European avalanche-warning
Scale	system.
Avalanche Size	D1 (sluff) … D5 (largest known).

Heat / cold#

Index	Notes
Heat Index	NWS; combines temp + RH; ≥ 90 °F caution, ≥ 130 °F extreme danger.
Wet-Bulb Globe Temp.	WBGT; outdoor work-rest standard.
Wind chill Humidex (Canada)	NWS WCT; combines temp + wind speed.

Solar / space weather#

Scale	Notes
NOAA G-scale (geo)	G1 minor … G5 extreme geomagnetic storm.
NOAA R-scale	R1 … R5 radio blackout.
NOAA S-scale	S1 … S5 solar radiation storm.
Kp index	0-9 planetary geomagnetic.
Dst index	equatorial geomagnetic; negative = stronger storm.
GOES X-ray	A < B < C < M < X solar-flare classification.

Industrial / nuclear#

Scale	Notes
INES	IAEA International Nuclear and Radiological Event Scale 0-7; 7 = Chernobyl + Fukushima.
NIMS Type	US National Incident Mgmt System; Type 1 = highest complexity.
ICS / IMS positions	command, operations, planning, logistics, finance & admin (the “general staff”).
WHO PHEIC	Public Health Emergency of International Concern; declared / not declared (binary).