Where does surge collide?

The abnormal rise of coastal sea level driven by a storm's winds and low atmospheric pressure, over and above the predicted astronomical tide. Proudman's 1929 The Effects on the Sea of Changes in Atmospheric Pressure worked out how a moving pressure disturbance forces water against a coast, giving the physical oceanography of what is now called a storm surge, and the Liverpool Tidal Institute built the empirical study of these events in the same period. The referent is a mass of seawater piled against a shore, measured in metres above the tide, and it is not a spike of voltage in a wire, a price that climbs with demand, or a hospital's room to take on more patients.[1]

Unit

One event's peak water level above the predicted tide, in metres

Recovery means

The piled water drains back as the storm passes and winds and pressure return to normal

Measured by

Recorded by coastal tide gauges as the residual between observed and predicted tide, and reconstructed by numerical surge models

A brief, steep rise of voltage or current above the normal operating level, often caused by lightning or by switching, that travels along a conductor as a wave. Bewley's 1933 Traveling Waves on Transmission Systems gave the classic analysis of how such surges propagate, reflect, and are clamped by protective devices, and the surge arrester that diverts them to ground had been in use since the early 1900s. The referent is a fast electrical transient in a circuit, timed in microseconds and rated in kilovolts, and it has nothing to do with a wall of seawater, a fare that rises at peak times, or a health system stretching to meet demand.[2]

Unit

A single transient overvoltage, its peak in kilovolts above the nominal level

Recovery means

The traveling wave decays and surge arresters divert the excess energy to ground

Measured by

Characterised by impulse testing with standard waveforms such as the 1.2/50 microsecond lightning surge, by peak voltage and rise time

A price that rises automatically when demand outstrips available supply and falls back when demand eases, used to ration a scarce service in real time. The construct traces to peak-load pricing, set out in Steiner's 1957 Peak Loads and Efficient Pricing, which showed why a good should cost more when capacity is tight, and the modern name and its use on ride-hail platforms were analysed by Cachon, Daniels, and Lobel's 2017 study of surge pricing with self-scheduling drivers. The referent is a number attached to a transaction, a multiplier on a base fare, and it is unrelated to a coastal flood, a voltage transient, or a hospital's ability to expand.[3][4]

Unit

A price for one transaction, often expressed as a multiplier on the base fare

Recovery means

The price returns to its base level once demand falls back within supply

Measured by

Tracked as the multiplier over base price and by the resulting change in quantity demanded and supplied

The ability of a hospital or health system to rapidly expand its services to handle a sudden, large rise in demand for care, such as a disaster or an epidemic. Hick and colleagues' 2004 Health care facility and community strategies for patient care surge capacity laid out the staff, space, and supply elements that let a facility scale up, and Barbisch and Koenig's 2006 Understanding Surge Capacity: Essential Elements refined the definition. The referent is an organisational and logistical property of a care system, counted in extra beds, staff, and supplies, and it is not a rise of the sea, a jump in voltage, or a change in price.[5][6]

Unit

The extra caseload a system can absorb above its normal level, in beds, staff, and supplies

Recovery means

The system stands down to baseline staffing and bed counts once the event passes

Measured by

Gauged against benchmarks such as an immediate increase in available beds and staff above daily capacity