Extreme Weather Event (EWE)

A subset of "Hazard" and "Threat" to CI comprise Extreme Weather Events (EWE) which causes a CI disruption or, even more often, a Common cause failure of multiple CI.

EWE comprise:

1. long duration drought
2. extreme precipitation in a short period of time (e.g., flash floods, water bombs)
3. (extreme) cold wave / cold snaps / ice & snow storms
4. (extreme) heat wave
5. extreme wind (hurricanes, tornadoes, Derecho, etc.)

Definitions

International Definitions

IPCC

Extreme Weather Event (EWE) is an event that is rare within its statistical reference distribution at a particular place.

Definitions of “rare” vary but an EWE would normally be as rare or rarer than the 10^th or 90^th percentile’

National Definitions

Australia

Australia has defined severe weather rather than extreme weather as:

Severe weather is any atmospheric condition potentially destructive or hazardous to human beings.

Severe weather is often associated with extreme convective weather (tropical cyclones, tornadoes, severe thunderstorms, squalls, etc.) and with storms of freezing precipitation or blizzard conditions.

United States NOAA

The U.S. National Oceanic and Atmospheric Administration (NOAA) uses a definition of extreme weather based on an event's climatologically-expected distribution. An event is called extreme if occurs, for example, only five per cent or less of the time. NOAA notes, however, that the exact choice of cut-off of the climatologically probability value used in the definition is somewhat arbitrary. A simple example of extreme weather is therefore when the temperature drops to a level which occurs less than five per cent of the time, say below -20 C. Extreme events, by definition, are rare.

See also

• Hydrometeorological Hazard
• Natural Hazard